Preservation of HMCS SACKVILLE

Transcription

Copy No. _____
Defence Research and
Development Canada
Recherche et développement
pour la défense Canada
DEFENCE
&
DÉFENSE
– Preliminary Options Study
Yueping Wang
Randy Haggett
Defence R&D Canada – Atlantic
Technical Memorandum
DRDC Atlantic TM 2010-104
November 2010
This page intentionally left blank.
- Preliminary Options Study
Yueping Wang and Randy Haggett
November 2010
Principal Author
Original signed by Yueping Wang and Randy Haggett
Yueping Wang and Randy Haggett
Approved by
Original signed by Leon Cheng
Leon Cheng
Head/DL(A)
Approved for release by
Original signed by Calvin Hyatt
Calvin Hyatt
DRP Chair
© Her Majesty the Queen in Right of Canada, as represented by the Minister of National Defence, 2010
© Sa Majesté la Reine (en droit du Canada), telle que représentée par le ministre de la Défense nationale,
2010
Abstract ……..
Defence R&D Canada - Atlantic was tasked to conduct an options study on the permanent
preservation of HMCS SACKVILLE. The main objectives were to evaluate options for the
preservation of HMCS SACKVILLE in a permanent site and to provide preliminary
recommendations for preservation options. A number of preservation options were evaluated,
including maintaining the Status Quo, corrosion control of interior hull structure, dry berth,
floating berth in seawater, and permanent enclosed docking berth. These options were evaluated
based on the information collected through literature review and site visits to the historic ships in
UK on which various preservation practices have been adopted. Among the options evaluated, a
permanent enclosed docking berth with weather-proof shelter was considered the most
appropriate for the preservation of HMCS SACKVILLE. This option will not only meet the
objective of preserving HMCS SACKVILLE in perpetuity, but also allow full public access to the
ship all year round without weather effect. In addition, measures that can be taken in the short
term to mitigate the corrosion damage to the interior hull structures were identified. Future work
based on the recommended preservation option was also recommended.
Résumé ….....
Recherche et développement pour la défense Canada - Atlantique a reçu le mandat d’effectuer
une étude sur les options de conservation archivistique permanente pour le NCSM SACKVILLE.
Les objectifs principaux étaient d’évaluer les options de conservation du NCSM SACKVILLE
sur un site permanent et de fournir des recommandations préliminaires pour les options de
conservation. Plusieurs options ont été évaluées, y compris maintenir le statu quo, contrôler la
corrosion de la coque intérieure, opter pour un poste de mouillage sec, un poste de mouillage en
eau de mer ou un poste de mouillage fermé permanent. Ces options ont été évaluées avec les
renseignements recueillis dans les analyses documentaires et les visites sur place de navires
historiques en Grande-Bretagne sur lesquels diverses méthodes de conservation ont été utilisées.
Parmi les options évaluées, un poste de mouillage fermé permanent muni d’un abri à l’épreuve
des intempéries a été considéré la plus appropriée pour la conservation du NCSM SACKVILLE.
Cette option ne respecte pas seulement l’objectif de conservation à perpétuité du NCSM
SACKVILLE, mais elle offre également au public un accès complet au navire à longueur d’année
tout en protégeant le navire des intempéries. De plus, on a identifié les mesures qui peuvent être
adoptées à court terme pour atténuer les dommages causés par la corrosion de la structure interne
de la coque. On a également recommandé des recherches futures basées sur l’option de
conservation suggérée.
i
ii
Executive summary
Preservation of HMCS SACKVILLE: - Preliminary Options Study
Yueping Wang; Randy Haggett; DRDC Atlantic TM 2010-104; Defence R&D
Canada – Atlantic; November 2010.
Introduction: The Canadian Naval Memorial Trust (CNMT) has the preservation of HMCS
SACKVILLE, as a Canadian Naval Memorial in perpetuity as its main objective. CNMT, with
approval from Commander Maritime Forces Atlantic, has tasked Defence R&D Canada - Atlantic
(DRDC Atlantic) to conduct an options study for the permanent preservation of the ship. The
objectives of this options study are to evaluate options for the preservation of HMCS
SACKVILLE in a permanent site, to identify the technical challenges of the preservation, and to
provide preliminary recommendations for preservation options and further studies. This report
summarizes the information collected through site visits, literature review, the hull inspection as
well as the laboratory testing results. Preliminary recommendations on optimal approaches for the
preservation of HMCS SACKVILLE in a permanent site are presented.
Results: The hull inspection and lab testing showed that there was extensive corrosion in the
interior hull plating and frames in both the engine room and boiler rooms. The corrosion damage
was mainly caused by the moist environment in the interior spaces. However, there was no
chloride involved in the corrosion process. The hull survey also showed overprotection of the
exterior underwater hull, caused by existing zinc anodes mounted on the wetted hull. Literature
review showed that dehumidification is a preferred corrosion control technique that can be used
for the corrosion control of the interior hull structure on HMCS SACKVILLE. Various
preservation options were evaluated, including existing practice of maintaining the ship, corrosion
protection measures for interior hull structures, dry berth, floating berth in seawater, and
permanent enclosed docking berth. These options were evaluated based on the information
collected through literature review and site visits to the historic ships in UK on which various
preservation practices have been adopted. Among the options evaluated the permanent enclosed
docking berth option with dehumidification in the interior bilge spaces and with weather-proof
shelter was considered the most appropriate for the preservation of HMCS SACKVILLE. This
option will not only meet the objective of preserving HMCS SACKVILLE in perpetuity, but also
allow full public access to the ship all year round without weather effect. In addition, measures
that can be taken in short term to mitigate the corrosion damage to the interior hull structures
were identified.
Recommendations: It is recommended that a permanent enclosed docking berth with weatherproof shelter and with dehumidification in the interior bilge spaces be adopted for the long-term
preservation of HMCS SACKVILLE. It is also recommended that a HMCS SACKVILLE
Preservation Project, as part of the effort to implement the short-term preservation plan, be
implemented as soon as can be arranged. This project, which includes dehumidification of the
interior bilge spaces and coating applications to slow down the corrosion process of the interior
hull structure, will help to stabilize the ship before it can be placed in the permanent enclosed
docking berth.
iii
Sommaire .....
Yueping Wang; Randy Haggett; DRDC Atlantic TM 2010-104; R & D pour la
défense Canada – Atlantique; Novembre 2010.
Introduction: L’objectif premier du Fonds de commémoration de la marine canadienne (FCMC)
est la conservation à perpétuité du NCSM SACKVILLE. Le FCMC, avec l’approbation du
commandant des Forces maritimes de l’Atlantique, a chargé R & D pour la défense Canada –
Atlantique (RDDC Atlantique) d’effectuer une étude sur les options de conservation permanente
du NCSM SACKVILLE sur un site permanent, d’identifier les défis techniques de conservation
et de fournir des recommandations préliminaires pour les options de conservation et les études
futures. Le présent rapport résume les renseignements recueillis lors de visites sur place,
d’analyses documentaires, d’inspections de coque et selon des résultats d’essai en laboratoire. Les
recommandations préliminaires des meilleures approches de conservation du NCSM
SACKVILLE sur un site permanent y sont également présentées.
Résultats: L’inspection de la coque et les essais en laboratoire ont démontré la présence de
corrosion importante à l’intérieur des bordés de carène sur l’ossature de la salle des machines et
de la chaufferie. La corrosion a été causée principalement par l’environnement humide retrouvée
à l’intérieur des compartiments. Toutefois aucun chlorure n’est à l’origine de la corrosion.
L’inspection de la coque a également démontré une surprotection de la carène par des anodes de
zinc existants montés sur la coque mouillée. L’analyse documentaire a démontré, quant à elle, que
la déshumidification constitue une technique de premier choix qui peut être utilisée pour contrôler
la formation de corrosion sur la coque intérieure du NCSM SACKVILLE. Diverses options de
conservation ont été étudiées, y compris le maintien des mesures de protection contre la corrosion
existantes pour les coques intérieures, le poste de mouillage sec, le poste de mouillage en eau
salée et le poste de mouillage fermé permanent. Ces options ont été évaluées en se basant sur les
renseignements recueillis par les analyses documentaires et les visites sur place de navires
historiques en Grande-Bretagne sur lesquels diverses méthodes de conservation ont été utilisées.
Parmi les options évaluées, le poste de mouillage fermé permanent avec déshumidification des
fonds de cale et un abri contre les intempéries a été considéré la méthode de conservation la plus
adéquate pour le NCSM SACKVILLE. Cette option ne respecte pas seulement l’objectif de
conservation à perpétuité du NCSM SACKVILLE, mais elle offre également au public un accès
complet au navire à longueur d’année tout en protégeant le navire des intempéries. De plus, on a
identifié les mesures qui peuvent être adoptées à court terme pour atténuer les dommages causés
par la corrosion aux structures de la coque intérieure.
Recommandations: On recommande l’adoption d’un poste de mouillage fermé permanent muni
d’un abri contre les intempéries et la déshumidification des fonds de cales pour assurer la
conservation à long terme du NCSM SACKVILLE. On recommande aussi qu’un projet de
conservation du NCSM SACKVILLE, dans le cadre d’un plan de conservation à court terme, soit
mis en œuvre le plus tôt possible. Ce projet qui comprend la déshumidification des fonds de cale
et l’application de revêtements pour ralentir la corrosion de la coque intérieure aidera à stabiliser
le navire avant qu’il soit placé dans un poste de mouillage fermé permanent.
iv
Table of contents
Abstract …….. ................................................................................................................................. i
Résumé …..... ................................................................................................................................... i
Executive summary ........................................................................................................................ iii
Sommaire ....................................................................................................................................... iv
Table of contents ............................................................................................................................. v
List of figures ................................................................................................................................ vii
List of tables ................................................................................................................................. viii
Acknowledgements ........................................................................................................................ ix
1
2
Introduction............................................................................................................................... 1
1.1
Objective........................................................................................................................ 1
1.2
Work Plan ...................................................................................................................... 1
Background ............................................................................................................................... 3
3
Hull Survey and Lab Testing .................................................................................................... 5
3.1
Interior Hull ................................................................................................................... 5
3.2
Exterior Hull .................................................................................................................. 9
3.3
Hull Survey during Docking Period ............................................................................ 13
4
Site Visit ................................................................................................................................. 15
4.1
HMS CAVALIER ....................................................................................................... 15
4.2
HMS WARRIOR......................................................................................................... 16
4.3
HMS ALLIANCE ....................................................................................................... 17
4.4
ss Great Britain ............................................................................................................ 18
4.5
Historic Ships 2009 ..................................................................................................... 21
Factors Affecting Interior Ship Hull Corrosion ...................................................................... 22
5.1
Humidity ...................................................................................................................... 22
5.2
Temperature................................................................................................................. 25
5.3
Dehumidification ......................................................................................................... 25
5.4
Coating Applications ................................................................................................... 26
5
6
Evaluation of Options ............................................................................................................. 28
6.1
Option 1 - Status Quo .................................................................................................. 28
6.2
Option 2 - Corrosion Control of Interior Hull Plating ................................................. 29
6.3
Option 3 - Dry Berth.................................................................................................... 29
6.3.1
Option 3(a) - Dry berth in open environment ............................................... 30
6.3.2
Option 3(b) - Dry berth with environmental control ..................................... 30
6.4
Option 4 - Floating Berth in Seawater ......................................................................... 31
6.5
Option 5 - Permanent Enclosed Docking Berth .......................................................... 31
v
6.6
Selection of Preferred Option ...................................................................................... 33
7 Recommendations and Future Work ...................................................................................... 34
7.1
Recommendations ....................................................................................................... 34
7.2
Future Work................................................................................................................. 34
References ..... ............................................................................................................................... 38
List of symbols/abbreviations/acronyms/initialisms ..................................................................... 41
Distribution list .............................................................................................................................. 43
vi
List of figures
Figure 1: Corrosion in the interior hull plates in the engine room. ................................................. 6
Figure 2: Photo showing extensive corrosion in the heads of the rivet. .......................................... 6
Figure 3: Photo showing corrosion in one of the frames in the engine room. ................................. 7
Figure 4: Water accumulated at the bottom of the bilge of HMCS SACKVILLE engine room..... 7
Figure 5: Condensation on the bilge hull plates in the engine room. .............................................. 8
Figure 6: Photo showing one spot on the hull plating where UT thickness gauging was
conducted in the engine room. ...................................................................................... 9
Figure 7: Graph comparing the open circuit potential of a steel hull, ideal cathodic protection
potential range and measured hull potentials on HMCS SACKVILLE. ..................... 11
Figure 8: Photo showing zinc anodes installed on the underwater hull of HMCS
SACKVILLE............................................................................................................... 11
Figure 9: Surface appearances of two coating coupons under cathodic protection for 2.5 years
at -850 mV (a) and at potentials between -1025 mV ~ -1070 mV (SSC) (b)............. 12
Figure 10: HMS CAVALIER berthed afloat at No. 2 Dry Dock in Chatham Historic
Dockyard. .................................................................................................................... 16
Figure 11: HMS WARRIOR berthed afloat along a jetty at Portsmouth Historic Dockyard. ...... 17
Figure 12: Stern of HMS ALLIANCE showing severe corrosion damage. .................................. 18
Figure 13: Top side of ss Great Britain. ........................................................................................ 19
Figure 14: View of ss Great Britain from under the glass envelope. ............................................ 20
Figure 15: Variation of relative humidity in Halifax Harbour (daily average) in 2009 [21]. ........ 23
Figure 16: Comparison of the temperature inside and outside of the engine room on HMCS
SACKVILLE............................................................................................................... 24
Figure 17: Comparison of the relative humidity inside and outside of the engine room on
HMCS SACKVILLE. ................................................................................................. 24
Figure 18: Comparison of the temperatures of the air in the Halifax Harbour and the
temperature of the water (1 m below water surface) in the Bedford Basin in 2009
[21, 23]. ....................................................................................................................... 25
vii
List of tables
Table 1: Exterior underwater hull potential survey results............................................................ 10
viii
Acknowledgements
The authors would like to thank MARLANT/FMFCS for their financial support of the site visit
trip to UK, and Cdr. Wendall Brown (retired), the Commanding Officer of HMCS SACKVILLE
and LCdr. Don Lowther (retired), the Engineering Officer, for their assistance in conducting the
hull inspection of the ship.
The authors would also like to thank Capt(N) Thomas Brown (retired), Cdr. Wendall Brown
(retired), Cdr. Donald Hussey (retired), LCdr. Don Lowther (retired), and LCdr. Robyn Locke of
MARLANT/FMFCS for their constructive comments and suggestions during the preparation of
this report.
The authors are very grateful to the following people for their time and effort in assisting our site
visits in UK: Mr. Richard Holdsworth of Chatham Historic Dockyard Trust, Mr. Bob Daubeney
of Portsmouth Historic Dockyard, Mr. J.J. Molloy of the Royal Navy Submarine Museum, and
Mr. Andy Curran of the Imperial War Museum.
The authors would also like to thank the following Defence R&D Canada - Atlantic Dockyard
Laboratory (Atlantic) staff for their contributions to this task: Dr. John Hiltz for his input on
coating applications; Dr. Royale Underhill for her input on corrosion preventative compounds;
and Mr. Luke MacGregor for his assistance in the in-situ hull thickness gauging.
ix
x
1
Introduction
The Canadian Naval Memorial Trust (CNMT) has the preservation of HMCS SACKVILLE, as a
Canadian Naval Memorial in perpetuity as its main objective. CNMT has been working with the
Halifax Harbour Waterfront Development Corporation to determine a permanent site on the
Halifax waterfront for the ship. It has been proposed that HMCS SACKVILLE be enclosed
within a permanent berth in the areas of ‘Queens Landing’, and be part of a refurbished Maritime
Museum of the Atlantic.
CNMT, with approval from Commander Maritime Forces Atlantic, has tasked Defence R&D
Canada - Atlantic (DRDC Atlantic) to lead an options study, with assistance from FMF Cape
Scott, for the permanent placement/configuration/preservation of the ship1,2.
1.1
Objective
Consultation with CNMT led to the following objectives for this options study:
1. Evaluating options for the preservation of HMCS SACKVILLE in a permanent site;
2. Identifying the technical challenges of the preservation; and
3. Providing preliminary recommendations for preservation options and further studies.
1.2
Work Plan
A work plan was developed based on the aforementioned objectives. The work plan included the
following approaches:
1. Evaluation of options for preservation of historic ships in a permanent site.
A literature review was conducted on the options for preservation of historic ships in a
permanent site. The literature review focused on various preservation techniques applied to
other national memorials including the pros and cons of different approaches to permanent
berthing of historic ships (dry berth, fresh water floating berth, or salt water floating berth).
Information was also collected through the literature review on life cycle maintenance
practices that used different preservation approaches for other historic ships.
Site visits were also conducted to other national ship memorials that use different permanent
berthing options (i.e., dry dock, salt water floating berth, and fresh water floating berth).
Information on the preservation and restoration of historic ships was also collected by
attending a conference on historic ships (Historic Ships 2009).
1
Canadian Naval Memorial Trust, “A proposed tasking for the permanent preservation of HMCS
SACKVILLE” Letter to Commander, Maritime Forces Atlantic, 29 June 2009.
2
Commander, Maritimes Forces Atlantic, “Preservation of HMCS SACKVILLE”, Letter to Chairman,
Canadian Naval Memorial Trust, 23 July 2009
1
2. Identification of technical challenges of the preservation.
This was conducted by reviewing previous hull survey reports, conducting detailed hull
inspection on HMCS SACKVILLE to evaluate corrosion protection performance of the
underwater hull, and to assess the extent of corrosion damage of the hull structure in the
bilge. Samples of bilge water, hull corrosion product and hull coating were taken and
analyzed in the lab. Literature on various corrosion protection measures (new coating
materials and application techniques, corrosion preventive compounds, cathodic protection,
humidity control, etc) was reviewed. A survey was also conducted on approaches that have
been used to deal with hazardous materials (e.g. asbestos) in historic ships.
3. Preliminary recommendation for options for the preservation.
Optimal approaches for the preservation of HMCS SACKVILLE in a permanent site were
recommended based on literature review, hull survey data, laboratory testing results, and a
spectrum of financial situations.
This report summarizes the information collected through site visits, literature review, the hull
inspection as well as the laboratory testing results. Preliminary recommendations on optimal
approaches for the preservation of HMCS SACKVILLE in a permanent site are presented.
The contents of the remaining sections in the report are arranged as follows: Section 2 describes a
brief history of HMCS SACKVILLE and the Flower Class corvettes. The hull survey results on
HMCS SACKVILLE and lab testing results are then described in Section 3. Section 4
summarizes the site visit trip to the historic ships with various preservation practices in UK. In
Section 5 literature review on the factors affecting interior ship hull corrosion is presented. This
follows with the evaluation of several options for the preservation of HMCS SACKVILLE in
Section 6. Finally, Section 7 presents the recommendations and future work based on the
evaluation results.
2
2
Background
The Flower Class corvette (also referred to as the Gladiolus class) was a class of 269 corvettes
used during World War II. HMCS SACKVILLE was one of more than 120 corvettes built in
Canada during that period. She was built at Saint John, NB and commissioned on 29 December
1941. HMCS SACKVILLE and other Canadian corvettes soon became the workhorses of the
North Atlantic, as anti-submarine convoy escorts during the Battle of the Atlantic [1].
The majority of the corvettes served during World War II with the Royal Navy (RN) and Royal
Canadian Navy (RCN), with some being built for, or transferred to, other Allied navies such as
the United States Navy (USN) (where some were manned by the U.S. Coast Guard), the Free
French Naval Forces, the Royal Netherlands Navy, the Royal Norwegian Navy, the Royal Indian
Navy, the Royal Hellenic Navy, the Royal New Zealand Navy and, immediately post-war, the
South African Navy. Several ships built largely in Canada were transferred between the USN and
RN under the lend-lease program, seeing service in both navies.
Most Flower class corvettes were scrapped shortly after the war, however, HMCS SACKVILLE
was laid up in reserve. For the full thirty years, from December 1952 when she was reactivated
until the same month in 1982, HMCS SACKVILLE served the interests of science. Her
usefulness and efficiency in that role is perhaps best measured by the simple fact that, of all
World War II vintage ships which operated as research vessels, and of those that might have been
converted for the purpose, HMCS SACKVILLE lasted longest. Her career as a research vessel
divides nicely into three distinct phases. For the first 10 years her work was balanced between
civilian and military, working on the joint committee on oceanography. From early 1960s to mid
1970s she concentrated primarily on biological and geological work under the direction of the
new Bedford Institute of Oceanography. In 1975, she went back almost exclusively to naval
work, supporting modern research into underwater acoustics by the Defence Research
Establishment, Atlantic (now Defence R&D Canada - Atlantic).
The ship was transferred to the Canadian Naval Corvette Trust (now the Canadian Naval
Memorial Trust) on 28 October 1983 and restored to her 1944 appearance (apart from minor
details in her camouflage and the presence of the "barber pole" red and white pattern around her
funnel which had been removed before 1944).
The original intention had been to acquire HMCS Louisburg (K401), which had been sold to the
Dominican Republic and renamed Juan Alejandro Acosta, but this vessel was wrecked (along
with another Flower-class corvette - Cristobal Colon, the former HMCS Lachute (K440)) by
Hurricane David in 1979. This left HMCS SACKVILLE as the sole remaining Flower class
corvette.
HMCS SACKVILLE currently serves the summer months as a museum ship moored beside the
Maritime Museum of the Atlantic in Halifax, Nova Scotia, while spending her winters securely in
the naval dockyard at CFB Halifax under the care of Maritime Forces Atlantic, the Atlantic fleet
of Canadian Forces Maritime Command. Her presence in Halifax is considered appropriate, as the
port was an important North American convoy assembly port during the war.
3
Of those 269 corvettes that made Allied victory in the Atlantic possible, HMCS SACKVILLE is
the only ship to be preserved as a museum ship.
4
3
Hull Survey and Lab Testing
The hull survey focused on visual inspection of the interior surface of the riveted shell plates in
both the engine room and boiler room. The electric potentials on the exterior hull surface were
also conducted during the hull survey.
3.1
Interior Hull
Visual inspection was conducted in Mid-December 2009 on the interior surface of the hull plates
in both the boiler rooms and the engine room. There were two fire-tube boilers in two separate
boiler rooms in the middle of the ship. Aft of the boiler rooms lay the engine room. There are fuel
tanks on either side of the boiler rooms, but the engine room remains separated from the sea only
by the thin steel plates of the hull. The machinery (engine room and boiler rooms) takes up the
entire midship section (about half the length of the ship). The engine room and each of the boiler
rooms are fitted in the open spaces from the bilge and the roof windows of the superstructure.
The hull plating in the engine room showed extensive corrosion, in particular in the plating below
the water line, as shown in Figure 1. Corrosion with various extents was also visible in the heads
of the rivets (Figure 2) and in the frames (Figure 3). The paint coating applied on the interior hull
did not seem to provide much protection to the underlying riveted plates. In fact thick corrosion
scales had already developed under the coating. At the time of inspection workers were removing
the loose corrosion product from the hull plates. More than 500 pounds of the paint coating and
corrosion product was removed at that time, with more corrosion product removed since then.
One piece of corrosion product, measuring 22 cm long and 17 cm wide, was taken back to the
Dockyard Laboratory for further analysis. The thickness of the corrosion product, including the
coating, ranged from 4.0 mm and 7.7 mm.
There was more than 30 cm of water accumulated at the bottom of the engine room (Figure 4).
Leaks from the steam lines in the engine room had been reported at two spots and had been fixed
at the time of inspection. Condensation was also evident in the engine room during a follow on
hull inspection, as shown in Figure 5. Condensation takes place on the interior hull plating when
the temperature on the interior hull surface reaches or is lower than the dew point in the engine
room.
There was also water accumulated at the bottom of the boiler room. Part of the side plating in the
boiler room was wet. Further inspection showed that water was seeping out of the plating that
separates the boiler room and the fuel tank, which was used as a water ballast tank at the time of
inspection.
5
Figure 1: Corrosion in the interior hull plates in the engine room.
Figure 2: Photo showing extensive corrosion in the heads of the rivet.
6
Figure 3: Photo showing corrosion in one of the frames in the engine room.
Figure 4: Water accumulated at the bottom of the bilge of HMCS SACKVILLE engine room.
7
Figure 5: Condensation on the bilge hull plates in the engine room.
Ultrasonic thickness (UT) gauge technique was used to conduct thickness gauging of the
underwater hull plating. The Panametrics 37DL Plus UT gauge was used. Prior to the in-situ
measurement the UT gauge was calibrated using a standard steel sample supplied by the
manufacturer. Then, the UT gauge was tested on a 350WT plate with/without coating on the
opposite side of testing surface. It was also tested with the opposite side submerged in water. It
was found that neither the coating nor water on the opposite side of the testing surface affected
the testing results.
Two spots on the starboard side of the engine room were selected for the measurement. Corrosion
scale was removed from the two spots, located 60 cm below the waterline. At first the thickness
reading could not be obtained, possibly due to the roughness of the surface area. After the
surfaces were smoothed using an electric grinder good readings were obtained. At one spot the
readings were 9.50 mm, 9.48 mm and 9.46 mm. At another spot, the readings were 9.35 mm and
9.20 mm. For reference 3/8 inch is equivalent to 9.525 mm. Figure 6 shows one spot where the
UT thickness gauging was conducted.
Lab testing, at DRDC Atlantic Dockyard Laboratory (Atlantic), was conducted on water samples
taken from the boiler room and the engine room, as well as a small piece of the corrosion product
removed from the hull plating in the engine room.. The testing found no chloride in both the
water samples and the corrosion product. X-ray diffraction analysis showed that the corrosion
scale consist primarily of magnetite, Fe3O4. The analysis results indicate that there was no
seawater ingress into both the engine room and the two boiler rooms.
8
In brief, based on the visual inspection and the lab testing results, the moisture in both the boiler
rooms and the engine room is believed to be the major contributing factor for the corrosion of the
interior hull plating and other structure components. There was no chloride involved in the
corrosion process as no chloride was found in either the water at the bottom of the machinery
compartments or the corrosion product removed from the engine room. The major source of water
was found to be from the leak from the steam lines in the two rooms, condensation on the hull
plating and the leak from the fuel tanks (to the boiler rooms only). In addition, water ingress
through gaps and holes in the superstructure and from the entrances also likely contributed the
water accumulation.
Figure 6: Photo showing one spot on the hull plating where UT thickness gauging was conducted
in the engine room.
3.2
Exterior Hull
The survey on the electric potentials of the exterior underwater hull was conducted on February
24, 2010. A portable silver/silver chloride (SSC) reference electrode (GMC Staperm Model AG4-PT2) and a digital multimeter were used to measure electric potentials around the ship hull.
Two 6-foot long Plexiglas tubes were used to help position the reference electrode near the hull
surface. The hull potential readings are presented in Table 1.
9
Table 1: Exterior underwater hull potential survey results.
Location
Potential (mV vs.
Ag/AgCl)
Location
Potential (mV vs.
Ag/AgCl)
Starboard, opposite of
Anchor winch
-1020
Port, opposite of
Anchor winch
-1030
Starboard, 15’ fore of
Bridge
-1022
Port, 15’ fore of
Bridge
-1033
Funnel
-1035
Port, opposite of
Funnel
-1035
pom-pom gun
-1037
Port, opposite of
pom-pom gun
-1038
Stern
-1035
Bow
-1028
An open circuit potential is the potential a metal or alloy establishes when immersed in an
electrolyte. The open circuit potential of a steel hull in seawater is around -650 mV (SSC). The
recommended electric potential for the cathodic protection of a steel hull is -850 mV (SSC), with
potentials between -800 mV and -900 mV as a reasonable potential range for adequate cathodic
protection, as illustrated in Figure 7. This cathodic protection criterion is currently adopted in the
shipboard impressed current cathodic protection (ICCP) system onboard the Canadian Patrol
Frigates. Table 1 shows that the potential readings around the underwater hull were between
-1020 mV and -1038 mV (SSC). The underwater hull of HMCS SACKVILLE is protected by
zinc anodes. The fact that the range of the potentials on the steel hull is very close to the open
circuit potential of the sacrificial anodes (around -1050 mV (SSC)) indicates that likely too many
zinc anodes have been used for the protection of the underwater hull. It was noted that during the
docking period in October 1983, the capacity of the cathodic protection system on board HMCS
SACKVILLE was increased to that used on a ship five times her size [1]. This means much more
zinc anodes than normally needed were installed on the underwater hull. In addition, her bronze
propeller, which would consume significant portion of the current provided from the anodes, was
also removed from the ship. It is believed that the same cathodic protection practice has been used
since then. The photos taken during the docking period in 2008, e.g. Figure 8, show that there
were over 70 zinc anodes bolted to the underwater hull.
The hull potential readings indicate that the underwater hull is overprotected by the existing zinc
anodes. Although the overprotection at these potential levels will not cause corrosion of the steel
hull, the overprotection will likely cause premature damage to the coating applied on the hull
surface. The premature coating failure at these potential levels (e.g. -1020 to -1040 mV) has been
observed during the long-term coating coupon testing conducted at the Dockyard Laboratory
(Atlantic) 3. The 2.5 year-long testing showed extensive blistering of the paint coating and
excessive calcareous deposit on the coupons under cathodic protection at potentials between
3
Unpublished Dockyard Laboratory (Atlantic) testing results.
10
-1030 mV and -1070 mV (SSC), as shown in Figure 9. In comparison, the coupon that was
protected at -850 mV (SSC) showed very moderate coating blistering.
-400
Potential (Ag/AgCl, mV)
-500
-600
Open circuit potential of steel hull
-700
-800
-900
-1000
Ideal cathodic protection potentials
Measured underwater hull potentials
-1100
-1200
-1300
Figure 7: Graph comparing the open circuit potential of a steel hull, ideal cathodic protection
potential range and measured hull potentials on HMCS SACKVILLE.
Figure 8: Photo showing zinc anodes installed on the underwater hull of HMCS SACKVILLE.
11
(a) at -850 mV (SSC)
(b) at -1025 mV ~ -1070 mV (SSC)
Figure 9: Surface appearances of two coating coupons under cathodic protection for 2.5 years at
-850 mV (a) and at potentials between -1025 mV ~ -1070 mV (SSC) (b)
The predominant electrochemical reaction on the steel hull under cathodic protection in seawater
is oxygen reduction, as given in Equation 1:
O2 + H 2O + 4e − → 4 HO −
(1)
In addition, hydrogen evolution reaction may also take place at the potentials close to the open
circuit potential of the zinc anode, as given in Equation 2:
12
2 H 2 O + 2e − → H 2 + 2 HO −
(2)
Both cathodic reduction reactions will cause a rise in pH due to hydroxide ion production. In
seawater, calcareous deposits may form on the surface due to the increase in pH which occurs as
a result of cathodic reactions. Therefore, more negative protection potentials will lead to more
calcareous deposit as a result of higher pH levels on the cathodic protection surfaces. The
evolution of hydrogen gas on the underwater hull surface may have also contributed to the
premature blistering of the paint coatings.
A 7-year maintenance cycle is currently adopted for HMCS SACKVILLE. During each docking
period the old paint coating is removed by sand blasting and a new paint coating is applied. The
discussions in the preceding sections point to the fact that the paint coating should be able to last
longer if the hull potential can be maintained in the ideal potential range. This also implies that
the maintenance cycle of HMCS SACKVILLE can be extended if the major task of the dry
docking is to replace the underwater hull coating.
3.3
Hull Survey during Docking Period
A survey was conducted on the hull structure and superstructure by the Hull Surveyors from
FMFCS during the docking period in 2008. As the focus of the survey was to identify required
maintenance work, the survey reports did not include detailed description of the extent of
deterioration of the hull structure. The highlights of the survey data are summarized as follows:
1. Leaks were observed in several steel boxes, that have been welded to the hull to blank
redundant overboard discharge and/or cover damaged or wasted areas of shell plating [2].
The affected areas were located below waterline between Frames 74 and 77 in way of the
engine room. Recommendations were made to remove these steel blanking boxes, further
survey the exposed areas of shell plating for excessive damage/corrosion/wastage, and
weld in place new ¼” thick steel doubler plates. The reports of the further survey of the
shell plating were not available; however the lab testing results on the water sample from
the engine room did not indicate any leak of the seawater through the shell plating in way
of the engine room.
2. The survey also identified a number of areas in the tiller flats and in both starboard side
and port side of the bow that showed holed or wasted shell plating, and recommended use
of doubler plates to blank these areas [3, 4]. Wasted sections of shell plating in the engine
room were also reported during the survey and the required work was identified in the
report [4]. Two locations of the shell plating between the 3rd frame from forward
bulkhead and 2nd frame from forward bulkhead showed corrosion damage but no
perforation of the shell plating. As the locations were above the water line, it was
recommended by the Hull Surveyors that the entire section of the hull in these areas be
doubled at next available docking.
13
3. The No. 4 water ballast tank was also surveyed [5]. Pitting at various locations was
observed throughout the tank and on the longitudinal bulkhead. Recessed rivets were also
observed in two locations in the tank. The recommendations included cleaning to bare
metal, re-survey and grind areas of pitting (approximately 25) to determine shell plate
thickness by UT. The recommendations also included repairing recessed rivets by
welding.
14
4
Site Visit
There are several existing practices that can be adopted for permanently preserving a ship,
including dry dock, salt water floating berth, and fresh water floating berth. As HMCS
SACKVILLE was the first Canadian naval ship intended to be preserved in a permanent site,
there was not much experience to be learned within Canada. In order to meet and talk to people
who have experience and expertise in the preservation and restoration of historic ships, it was
decided to conduct a site visit to several national ship memorials in UK. The site visit trip took
place between 18th and 22nd November 2009 and the sites visited covered aforementioned three
permanent berthing options, which included HMS CAVALIER (fresh water floating berth), HMS
WARRIOR (salt water floating berth), HMS ALLIANCE (dry dock), and ss Great Britain (dry
dock). During the site visit trip, one of the authors also attended a conference on historic ships
(i.e. Historic Ships 2009). In addition, an opportunity was also taken during another business trip
in May 2010 to visit HMS BELFAST, which is held afloat in the Thames in London.
4.1
HMS CAVALIER
HMS CAVALIER is the only surviving Royal Navy's destroyer dating from World War II [6].
Built in 1944 at Samuel White's Isle of Wight yard, HMS CAVALIER served during the war in
the Arctic and the Western Approaches before joining the British Pacific Fleet as the war came to
a close. Refitted and modernized in 1957 she continued to play an active role as part of the Royal
Navy's Far East and Home fleets until she paid off in 1972. Since then she has served as a
museum ship at a number of sites in UK. In 1998 HMS CAVALIER was transferred to Chatham
Historic Dockyard and is now held afloat in No. 2 dry dock in tidal river water (Figure 10). She
has been designated as a war memorial to the 142 Royal Navy destroyers sunk during World War
II and the 11,000 men killed in their service.
A number of measures were taken for the corrosion protection of the ship structure [7]. For the
interior hull structure, a dedicated effort was made to keep the bottom of the bilge out of water
and to maintain the bilge under a dry condition. The measures taken include sealing all holes,
gaps along the upper deck and superstructure, emptying all ballast tanks, and carefully managing
all hatch openings to the bilge to minimize moisture ingress into the bilge. Paint coating was also
applied on the bilge surface after water was pumped out. This also covered the hard-to-access
areas in which case paint was sprayed on the metal surface. It was observed during the site visit
these measures have effectively stopped water leak to the bilge and maintained the bilge in a good
condition. For the exterior underwater hull, 12 sacrificial anodes, approximately 1.2 m high and
10 cm in diameter each, are suspended on both sides of the ship hull (6 each side) and electrically
connected to the ship hull. The advantage of this arrangement of the anodes is the easy
replacement of the anodes when needed.
For any museum ships open to public asbestos in the ship needs to be managed to limit public
exposure to it. In the case of HMS CAVALIER their first approach was to remove asbestos in the
engine rooms and boiler rooms. The process was found not only to be expensive but also to have
caused more exposure of asbestos. Their approach was then changed to sealing all asbestos,
which proved to be acceptable.
15
It is worth mentioning that the operation of HMS CAVALIER as a museum ship has become
financially sustainable. Their success is attributed mainly to their efforts in attracting visitors, in
particular students, their family members, and veterans. In the summer of 2009 the Chatham
Historic Dockyard Trust made available accommodation onboard the ship for youth groups who
wish to stay onboard and experience life onboard a Royal Naval Destroyer. An elevator was also
recently installed, which allows seniors, veterans and wheelchair users to access the
compartments on the lower deck. In addition, the Historic Dockyard, where HMS CAVALIER
and two other ships are currently preserved and where HMS VICTORY and Oberon class
submarines were built, is one of the primary tour sites in the area.
Figure 10: HMS CAVALIER berthed afloat at No. 2 Dry Dock in Chatham Historic Dockyard.
4.2
HMS WARRIOR
HMS WARRIOR was one of the world’s first iron hulled armoured battleships, which served the
Royal Navy between 1862 and 1883. Listed as part of the National Historic Fleet, Core
Collection, she is now a museum ship in Portsmouth, United Kingdom (Figure 11).
The armour plates were installed along both sides of the 400-foot long ship hull between the
upper deck and the underwater hull 6 feet below the waterline. The armour plates are 4-inch thick
and are bolted through 9-inch thick teak to 0.5-inch thick hull plates. The hull plates in
unarmoured areas, e.g. bow, stern and bottom of the bilge, are 1.25 inch thick.
Although sitting in seawater, there were no major corrosion issues reported [8]. This may be
attributed to the combination of the thick plating hull and armour plates. It may also be due to the
successful restoration project which cost £8 million and lasted 8 years before she became a
museum ship in 1987 [9]. As one of the measures to control corrosion, all ballast tanks were
16
emptied, recoated, and then loaded with scrap steel as ballast. Cement was also applied at various
locations in the bilge for easy removal of the water collected at these spots. One such spot was
checked during the site visit. No water was observed and the cemented area was dry. Corrosion
product was observed in the magazine room but the bilge was dry. There were no leak issues,
either from the hull plating or from the superstructure. The new plates that were put on the upper
deck during the restoration phase were believed to have effectively resolved the leak issues.
There is no cathodic protection applied to the underwater hull. The current maintenance plan
includes drydocking the ship every 10 years using a nearby naval base to clean and repaint the
underwater hull. Efforts have been made to extend the maintenance cycle (e.g. through using a
better quality paint coating).
Figure 11: HMS WARRIOR berthed afloat along a jetty at Portsmouth Historic Dockyard.
4.3
HMS ALLIANCE
HMS ALLIANCE is the only surviving example of the Royal Navy A-class submarines. She was
commissioned in 1947 and paid off in 1973, and then used as static training boat until August
1979. Since 1981 the submarine has been a museum ship, raised out of the water and on display
at the Royal Navy Submarine Museum in Gosport.
Although dry-docked, the submarine sits on the cradle over the seawater. The cradle is so close to
the water that the bottom of the submarine keel is exposed to seawater at high tide. The particular
marine environment has caused extensive corrosion damage on the submarine exterior, in
particular the stern of the submarine (Figure 12). In addition, as many as 100 pigeons have been
nesting in the casings of the submarine in recent years. The bird droppings have caused additional
corrosion damage to the submarine hull. The current set up also prevents easy access and
17
economical maintenance to its exterior. Efforts were made to prevent the pigeons from using the
boat as nests, without success [10, 11]. Extensive restoration work is required to save the ship. A
major restoration program is planned, which includes reclaiming land beneath HMS Alliance
using a cofferdam and backfill and repairing the submarine exterior [12].
Figure 12: Stern of HMS ALLIANCE showing severe corrosion damage.
4.4
ss Great Britain
When the ss Great Britain was launched in 1842 as the first ocean going liner with wrought iron
hull and screw propulsion, she was then the biggest ocean going ship in the world at 322 feet
long. After a short transatlantic career she was engaged in taking emigrants to Australia and in
later life she was converted to a sailing ship. She was finally abandoned in the Falkland Islands in
1937, scuttled on the beach in Sparrow Cove, after more than 40 years use as a floating
warehouse [13].
In 1970, the ss Great Britain was salvaged and placed in Great Western Dockyard in Bristol
(where she was built) to become a museum ship since then. In 1990 it was observed that the
ironwork was corroding rapidly in the high humidity dry dock environment (>70% relative
humidity (RH) on average) due to climate, seepage of water through the dockside, faulty drainage
and a leaking caisson [14, 15]. The research showed that the once dried salt in the corrosion
product, bonded on the wrought iron hull, strongly attracted water from air at the high humidity
dry dock environment, causing accelerated corrosion of the substrate. Further research showed
that this chloride accelerated corrosion could be significantly minimized by lowering the relative
humidity to or below 20% [16]. The conservation plan was made based on the research results,
included establishing a seal (glass envelope) between the ship and the side of the dry dock, to
allow dehumidification of the ship below the water line, and sealing the weather deck to allow
dehumidification of the interior of the ship [15]. The £11.8 million conservation project was
completed and the ship was reopened to public in July 2005. The topside of the hull (from the
18
waterline to the gunwales) was treated in accordance with the conservation plan [15], see Figure
13. The ship hull below the glass envelope was not treated, Figure 14. Instead, the sealed
chamber under the glass envelope was controlled at 20±3% (RH) in order to mitigate the
corrosion process. The conservation was claimed to be a success and was backed by the RH
readings from 15 to 25% with minimal fluctuation [17]. On the other hand this conservation
approach is accompanied by high operating costs, with annual gas bill for operating two
dehumidifiers as high as £62,000 in 2007.
Figure 13: Top side of ss Great Britain.
19
(a) bow
(b) Starboard side
Figure 14: View of ss Great Britain from under the glass envelope.
20
4.5
Historic Ships 2009
Organized by the Royal Institution of Naval Architects, Historic Ships 2009 was held in London
on the 19th and 20th of November 2009. The papers presented at the conference covers a variety
of topics, including:
•
•
•
•
•
•
•
•
•
•
Materials and structural analysis, including appropriate material replacement, repair or
replication.
Propulsion systems, rigs and sails.
Layouts and the need to meet current safety legislation.
Techniques for conservation and restoration.
Recording and deconstruction.
The balance between preservation afloat or dry.
Maintenance of craft skills and training.
The case for the replication of key historic vessels.
The sourcing of technical / historic information on "important" ships.
Recent marine archaeological discoveries.
One presentation, which is of particular interest to the HMCS SACKVILLE Preservation project,
described the rescue and restoration of the ss NOMADIC. The ss NOMADIC, which was built at
the same time as the RMS TITANIC and RMS OLYMPIC to serve as a tender to RMS
TITANIC, is the only floating survivor of the TITANIC era and the last surviving White Star
Line vessel in the world.
Many parallels can be drawn between the ss NOMADIC and HMCS SACKVILLE. The ss
NOMADIC, as with HMCS SACKVILLE, has been recognized as a historically significant
vessel. Historical significance is based on a number of factors which make the vessel unique
among historic ships. Both vessels are the last surviving ships of their type. Both vessels have
served in various roles well beyond their expected life time. The ss NOMADIC served not only as
a tender-liner for White Star and Cunard lines but later as a floating restaurant. HMCS
SACKVILLE served during the Battle of the Atlantic as a convoy escort and later as a research
vessel and museum ship.
The restoration and preservation plan for the ss NOMADIC [18] can be used as a template for the
preservation of HMCS SACKVILLE, as it encompasses the range of options available from “do
nothing” to “restoring and preserving the ship in her original as-built condition”. Each of the
options, however, has an associated cost which must be considered and is based, primarily, on the
intended final berth.
21
5
Factors Affecting Interior Ship Hull Corrosion
This section focuses on the discussions on factors affecting the interior hull structure of a ship,
corrosion control measures, and coatings as well as coating application specifications that apply
to the interior hull plating of a ship.
5.1
Humidity
The corrosion of the interior hull structure, except for any surface submerged in water, is
atmospheric corrosion in nature. A fundamental requirement for electrochemical corrosion
process is the presence of an electrolyte. Thin film electrolytes tend to form on metallic surfaces
under atmospheric exposure condition, after a certain critical humidity level is reached.
Theoretically, a clean metallic surface in an uncontaminated atmosphere under constant
temperature will not corrode at a humidity level below 100%. However, in practice, due to the
presence of hygroscopic surface species, impurities in the atmosphere and small temperature
gradients between the atmosphere and metallic surfaces, a microscopic surface electrolyte tends
to form at significantly lower humidity levels. The critical RH for various metals is generally
greater than 50% [19]. For iron, a critical relative humidity of 60% has been reported [20].
The most important factor affecting hull structure corrosion in the bilge of a ship is moisture. In
the absence of moisture, most contaminants would have little or no corrosive effect. The high
humidity level in the atmosphere, condensation, and leaks from steam lines, ballast tank, gaps in
the superstructure, and open hatches all contribute to the moist environment in the bilge.
The variation of the humidity levels in Halifax Harbour in 2009 is presented in Figure 15. The
daily average humidity data were obtained at the Shearwater Jetty [21]. The figure shows
considerably high humidity levels through the entire year in 2009. In fact, based on the daily
average data there was only 2.5% of the time when the humidity levels dropped below 50%, and
7.2% of the time humidity levels were below 60%. The yearly average humidity levels reached
76.9%.
The temperature and humidity in the engine room on HMCS SACKVILLE was logged between
22 April 2010 and 21 June 2010 while alongside one of the jetties in CFB Halifax HMC
Dockyard, as shown in Figures 16 and 17, respectively. Also presented in the same figures are the
temperature and humidity data obtained at the CFB Halifax HMC Dockyard [22]. In general, the
figures show that both temperature and humidity level in the engine room followed the trends of
the temperature and humidity level monitored in the Dockyard. Both temperature and humidity in
the engine room, however, fluctuated at much smaller amplitudes than in the open atmosphere.
The average humidity level in the engine room over the two-month period was 75.9%, which is a
little higher than the average humidity outside the ship (69.3%). The water collected at the bottom
of the bilge may have contributed to the more humid condition in the confined space.
Figure 18 compares the monthly average air temperature recorded at the Shearwater Jetty [21]
and the water temperature (1 m below water surface) in the Bedford Basin in 2009 [23]. In
general the temperature of the water near the water surface followed the trend of air temperature.
On the other hand, the water temperature appeared to be warmer in both Fall and Winter, and
22
colder in both Spring and Summer than the air temperature. This data implies that the temperature
of the shell plating of HMCS SACKVILLE in both the engine room and the boiler rooms tend to
be lower than the air temperature in the Spring and Summer. Therefore, the water in the air has a
greater tendency to condense on shell plating in the bilge in the Spring and Summer than in the
Fall and Winter. In other words, the critical humidity level for the bilge shell plating will be lower
in the Spring and Summer than in the Fall and Winter due to the variation with the season of the
temperature differences between the shell plating and the air inside the bilge.
100
Relative Humidity (%)
90
80
70
60
50
40
30
27-Dec-09
27-Nov-09
28-Oct-09
28-Sep-09
29-Aug-09
30-Jul-09
30-Jun-09
31-May-09
01-May-09
01-Apr-09
02-Mar-09
31-Jan-09
01-Jan-09
20
Date
Figure 15: Variation of relative humidity in Halifax Harbour (daily average) in 2009 [21].
23
30
Outside
Inside the bilge
Temperature ( °C)
25
20
15
10
5
2010-06-21
2010-06-16
2010-06-11
2010-06-06
2010-06-01
2010-05-27
2010-05-22
2010-05-17
2010-05-12
2010-05-07
2010-05-02
2010-04-27
2010-04-22
0
Date
Figure 16: Comparison of the temperature inside and outside of the engine room on HMCS
SACKVILLE.
100
Relative Humidity (%)
90
80
70
60
50
40
30
20
Outside
10
Inside the bilge
2010-06-21
2010-06-16
2010-06-11
2010-06-06
2010-06-01
2010-05-27
2010-05-22
2010-05-17
2010-05-12
2010-05-07
2010-05-02
2010-04-27
2010-04-22
0
Date
Figure 17: Comparison of the relative humidity inside and outside of the engine room on HMCS
SACKVILLE.
24
20
Air
Water
Temperature (°C)
15
10
5
0
-5
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
-10
Month
Figure 18: Comparison of the temperatures of the air in the Halifax Harbour and the
temperature of the water (1 m below water surface) in Bedford Basin in 2009 [21, 23].
5.2
Temperature
In general, a decrease in temperature will reduce the rate of corrosion of metals if other
conditions, such as RH, remain unchanged. However, for interior spaces an increase in RH
associated with a drop in temperature has an overriding effect on the corrosion rate. In other
words, simple air conditioning that lowers the temperature without additional dehumidification
will accelerate atmospheric corrosion rate [24].
5.3
Dehumidification
Dehumidification is a preferred corrosion control technique that has been used to protect aging
aircraft, military weapons and other assets from corrosion [19, 25, 26]. For example, Dynamic
dehumidification is one of four processes used for corrosion protection of the United States
military weapons and equipment [19]. Dynamic dehumidification technology uses closely
controlled and monitored dry-air to keep materials corrosion free. This technology was initially
used to preserve equipment that was to be out of service for long periods, but became more
common in its use in operational equipment or for the short-term rotation of equipment over the
last 50 years. In the Department of Defence applications, Dynamic dehumidification systems are
designed to achieve results by guaranteeing a RH <40% more than 90% of the time and a RH less
than 50% all of the time in most operational environments [19]. Dehumidification and vapor
25
phase corrosion inhibitors as corrosion control methods for US Navy advanced double hull naval
ships were also evaluated [27]. The results indicate that the dehumidifier is providing the best
environment and corrosion control. Logis-Tech Inc. and Munters are two of the major suppliers
of a variety of dehumidification units [28, 29].
It is noted that the RH required for corrosion protection in most applications (<50%) is
considerably higher than that required in the preservation of the ss Great Britain (~20%). This is
due to the fact that chloride is involved in the corrosion process of the hull structure in the ss
Great Britain, while in other dehumidification applications chloride is not involved in the
corrosion process.
5.4
Coating Applications
There are several critical factors that affect the effectiveness and lifetime of coatings used on ship
structures. The first is surface preparation. Coatings will not adhere to wet or dirty surfaces no
matter how advanced the coating. Dirty is a term that can apply to oily residues, grease, grime,
scale, and corrosion deposits. Different paint systems are specified for different locations (areas)
on a ship and for each of these locations there is also a surface preparation specification. To
maximize the effectiveness and lifetime of the coating system, it is essential that the surface be
prepared as specified. Once the surface has been prepared, it is also critical that it be protected
(coated) within the time indicated in the specification.
The second is that coatings must be applied under the conditions recommended by the coating
manufacturer. Care must be taken to ensure that the ambient air temperature and the temperature
of the surface to be coated are within the range recommended by the manufacturer. If the
temperature is too low, the coating will not cure. Cold metal and high RH result in the
condensation of moisture on the surface to be coated. The moisture will affect the adhesion of the
coating to the surface. If the temperature is too high, the coating may not cure in a manner that
ensures adhesion to the underlying coatings or surface. It is also important to apply the coating at
or near the thickness recommended by the manufacturer. This will maximize the protection that
the coating provides to the underlying surface.
The third is that overcoat times listed by the coating manufacturer be followed. In general both a
minimum time before overcoating and a maximum time between coats are listed. The former
ensures that the coating has had time to cure and the later that the next coat will adhere to the
previous coat. Care must also be taken to ensure that the surface to be overcoated is not
contaminated with dirt, oil, and grease prior to the application of the next layer of paint.
The surface preparation and coating system to be used on a ship depends on at least two factors.
The first is the condition of the coating that is already in place and the second is the location of
the surface to be coated. If the coating is largely intact it may not be necessary to completely
remove the coating. The steps required to prepare the surface in this instance will be different
than if the coating has deteriorated to the point where it is necessary to completely strip the
surface prior to recoating. The coating system specified for a particular surface depends on its
location on the ship. For instance, the coatings used on the exterior hull above and below the
waterline are different. Similarly, the coating system used in a bilge is different from the coating
system used on interior bulkheads.
26
The surface preparation and painting systems, that is, primer and top coats, recommended for use
on HMCS Sackville are based on those specified in “Specifications for Maintenance Painting of
HMC Ships” [30]. The document includes all specifications on the surface preparation and
painting systems for different areas of a ship, for instance, external hull above water line, external
hull below water line, bulkheads, bilges, machinery spaces above water line and machinery
spaces below the water line, etc.
27
6
Evaluation of Options
Several preservation options have been assessed for their relative ability to achieve the main
objective of the project: the preservation of HMCS SACKVILLE in perpetuity. The following
factors were also considered when assessing these options:
1) Public access
2) Evacuation in event of fire, and accessibility for emergency services
3) Need for periodic dry-docking, resulting in loss of revenue
4) Risks when under tow
5) Risk of damage from the wash of passing vessels, and the risk of collision
8) The extra cost of maintenance, being afloat
6.1
Option 1 - Status Quo
•
Place the ship alongside the jetty near Maritime Museum of the Atlantic for public
visit in summer and fall
•
Tow the ship back to CFB Halifax HMC Dockyard for housekeeping and minor
maintenance in winter and spring
o
Remove loose corrosion product in the bilge
o
Touch up the affected surfaces with paint coating
o
Daily house keeping
•
Dry-dock the ship every 7 years for major maintenance (e.g. recoating the underwater
hull)
•
Conduct a hull survey during the docking period and repair any affected areas when
necessary
This option would adopt the existing way to manage the ship maintenance. Severe corrosion has
occurred in the interior shell plating. The corrosion was caused by the humid environment in
these interior spaces with average humidity level of 76.9%. If no measures were taken to halt or
slow the corrosion process the shell plating will continue to corrode and eventually compromise
the integrity of the hull structure. The rivets would likely lose their function due to severe
corrosion before the shell plating is holed. This would increase the risk of losing the ship as a
result of flooding.
28
There would also be a high risk of damage to the ship from the wash of passing vessels, the risk
of collision, and risk of causing damage to other ships moored nearby, in particular during the
hurricane seasons, as happened in September 2003 during Hurricane Juan [31].
In brief, maintaining status quo is not really an option. While seeking the solution for
permanently berthing HMCS SACKVILLE may take some time, many measures can be taken
immediately to mitigate the existing corrosion problems before a permanent berth site can be
chosen. Some of the measures are described in the option that follows.
6.2
Option 2 - Corrosion Control of Interior Hull Plating
•
Recoat all interior hull plating and frames below and around waterline in accordance
with “Specifications for Maintenance Painting of HMC Ships” [30].
•
Install a dehumidification system in all enclosed interior spaces that cover the hull
plating below and around waterline. Control the humidity level below 40% RH 90%
of the time and below 50% RH all the time.
•
Empty all water-based and oil-based ballast tanks and use scrap metal as ballast
instead. Recoat the interior tank surface, and extend the dehumidification system to
the interior spaces of the ballast tanks.
•
Continue to use CFB Halifax HMC Dockyard for minor maintenance in winter.
•
Continue to use the HMC Dockyard docking facilities for major maintenance
Adoption of this option would effectively control the corrosion of the hull plating and frames in
the interior hull spaces and, therefore, minimize further corrosion damage to the interior hull
structure. More importantly, these corrosion control measures can be taken immediately without
waiting for the final determination on the permanent berthing option.
Implementation of these corrosion control measures alone, however, will not be able to achieve
the goal of preserving the ship in perpetuity. The risk to the ship from the wash of passing vessels
and the risk of collision, as described in the preceding section, remain when the ship is berthed
alongside the jetty. In addition, public would not have access to the ship during winter and spring.
6.3
Option 3 - Dry Berth
•
Construct a new dry dock
•
Permanently dry dock the ship
•
Conduct maintenance at the same dry dock
If this option were adopted, the dry-dock site would likely be on the Halifax waterfront near
Maritime Museum of the Atlantic. In addition to the requirement for public access, all
29
maintenance work would have also to be carried out on site. This would require the dry-dock site
to be constructed to facilitate all maintenance work required for the historic ship.
There are also two secondary options to be considered under this option: (1) dry berth in open
environment; and (2) dry berth with environmental control.
6.3.1
Option 3(a) - Dry berth in open environment
Examples of permanently dry-docking historic ships in open environment are HMS VICTORY in
Portsmouth, UK and Cutty Sark in Greenwich, UK. This option will not reduce the corrosion rate
of the interior shell plating due to the fact that similar humid environment will be present in both
outside the ship and the interior spaces on HMCS SACKVILLE. In addition, when dry-docked
the underwater hull will be losing cathodic protection, and as a result, will be exposed to the
damp environment in the dry dock. More frequent maintenance would be needed for the
underwater hull if the same level of corrosion protection as when she is afloat were to be
maintained.
6.3.2
Option 3(b) - Dry berth with environmental control
One example of permanently dry-docking historic ships in controlled environment is the ss Great
Britain in Bristol, UK. The environmental control means the control of the humidity in both
interior spaces and outside the ship to a predetermined level. A glass roof could be built over the
whole ship completely over the masts. Alternatively, a glass seal could also be built above the
weather deck or at the waterline. However, the glass roof would be extremely intrusive,
destroying the dry-dock context and, therefore, substantially reducing the quality to the visitor.
Furthermore, the major disadvantage of these approaches would be the considerably high cost for
dehumidifying the big sealed spaces. In the case of the ss Great Britain where a glass seal along
the waterline and the walls of the dry-dock forming sealed space for the underwater hull, two
giant dehumidification machines are used to dehumidify both interior and exterior sealed spaces
with annual gas bill of £62K.
One advantage of a dry berth arrangement is that there would be no need to find a dry dock for
periodic docking for underwater hull maintenance, saving the cost of dry-docking, towage and
associated insurance. This is particularly true in UK due to diminishing shipyard resources [32].
For instance, HMS BELFAST had to be towed from the Thames in London to Portsmouth on the
south coast of England for dry-docking due to the closure of the dry docks on the Thames and
Chatham Naval Dockyard [32, 33]. Finding a dry dock for HMCS SACKVILLE, however, is not
an issue. In fact, she has enjoyed the convenience of using CFB Halifax HMC Dockyard for drydocking and will still be able to access this resource in the foreseeable future.
Furthermore, ships are designed to withstand the crushing force of water outside, and are not very
well suited to remaining out of the water for prolonged periods unless very well supported. In the
case of Cutty Sark it was believed the supports used at the time when she was dry-docked in 1954
would allow her to remain out of the water for an indefinite period without the hull losing shape.
However, by the 1970's it was realised that the ship was losing shape as a result of wastage of the
ironwork that was worse than anticipated, and additional 31 intermediate frames had to be fitted
to maintain the shape of the hull [34]. The same scenario is occurring with the ss Great Britain.
30
6.4
Option 4 - Floating Berth in Seawater
•
Construct a floating berth facility that includes partially enclosed water area to
separate the ship from the passing vessels in the Harbour and other vessels moored
nearby.
•
plating below and around waterline. Control the humidity level below 40% RH 90%
of the time and below 50% RH all the time.
•
Continue to use CFB Halifax HMC Dockyard for minor maintenance in winter.
•
Redesign underwater hull cathodic protection system to maintain the electric
potential of the underwater hull at -850±50 mV (SSC)
•
Continue to use the CFB Halifax HMC Dockyard docking facilities for major
maintenance
This option will effectively control the humidity levels in all enclosed interior spaces below the
water lines and, therefore, reduce the corrosion rate of the interior steel shell plating to a
negligible level. The optimized cathodic protection measures would not only ensure adequate
corrosion protection of the underwater steel hull, but also avoid excessive calcareous deposits on
the underwater hull as a result of overprotection.
Technically, the afloat option has the advantage that the light hull structure is better supported,
i.e. no point loads in way of keel blocks, sten struts and shores. The ship will move a bit, and this
will help to disperse rain water which accumulates in fixed positions on the deck and upper
works.
The berthing option would also effectively separate the ship with the ships passing the harbour
and the vessels moored nearby and, therefore, avoid potential damage caused by collision with
other vessels and avoid causing damage to other vessels moored nearby.
One disadvantage is that there would be no public access to the ship in winter and spring due to
the harsh weather conditions and due to the requirement for minor maintenance. The ship would
also need to be towed back to CFB Halifax HMC Dockyard for any urgent repairs.
In addition, the movement that helps with drainage would lead to wear and tear on access
gangways. A mooring system will be required, and this must be monitored and maintained.
6.5
Option 5 - Permanent Enclosed Docking Berth
•
Construct a dry dock, for example a graving dock, on the Halifax waterfront and use
the dry dock as the permanent docking berth for HMCS SACKVILLE. The dry dock
could include resting blocks for the ship to be lowered onto for minor maintenance
and emergency repairs.
31
•
Include a gate as part of the dry dock to keep the dry dock water tight. The gate could
be opened to allow the ship to be towed away for major maintenance. The dry dock
could be filled with either seawater or fresh water. A circulation system could be
installed to ensure the water remains attractive and savoury. A pumping system could
also be installed to maintain a preset water level in the dry dock when the ship is
floating berthed and to pump out water for maintenance.
•
Construct a weather-proof shelter to cover the whole dry dock and the ship.
Depending on the design of the shelter a ventilation system in the shelter could be
installed.
•
plating below and around waterline. The humidity level could be controlled below
40% RH 90% of the time and below 50% RH all the time.
•
Redesign underwater hull cathodic protection system to maintain the electric
potential of the underwater hull at -850±50 mV.
•
Continue to use CFB Halifax HMC Dockyard docking facilities for major
maintenance
Examples of permanent enclosed docking berth are HMS CAVALIER [6] and HMS GANNET
[34] at Chatham Historic Naval Dockyard in UK. One difference between this option and the
aforementioned berth method in UK is that HMCS SACKVILLE will be placed in a permanent
enclosed docking berth that is covered by a shelter.
This option would allow the ship to be afloat in the indoor dry dock and, therefore, allow access
for the public all year round. Such an enclosed structure would protect the ship from the effects of
passing vessels and tidal changes, and eliminate the risk of collision with other vessels. The dry
dock design will also allow minor maintenance of the underwater hull or emergency repairs to be
carried out at the same dry dock. With the gate the ship could also be taken to the HMC Dockyard
for periodic maintenance.
The partial environmental control in this context means use of dehumidification in the interior
spaces and use of a ventilation system in the shelter. Use of dehumidification in all interior spaces
and introduction of redesigned underwater hull cathodic protection system will be able to
effectively control the corrosion damage of both interior and exterior underwater hull plating. In
addition, placing the ship in the indoor environment will avoid the effect of weathering on the
coatings on the above-water hull plating and on the superstructure and, therefore, extend the
service life of the coating. This option will also be able to reduce water ingress into the bilge from
open hatches and gaps in the superstructure and, as a result, help to control the humidity level in
the interior spaces.
Although either seawater or fresh water can be used in the dry dock, there are more advantages on
using fresh water than using seawater. Keeping the ship afloat in fresh water will extend the
maintenance cycle of the exterior hull coating by eliminating marine growth on the underwater
hull, and by reducing the corrosion damage to the hull in the splash zone owing to much less
32
corrosivity of fresh water than seawater. In addition, a dry dock filled with fresh water in an
enclosed space will produce less corrosive environment than with seawater.
Furthermore, this option will significantly reduce the number of requirements for towing the ship
back and forth between the permanent berth site and the CFB Halifax HMC Dockyard and,
therefore, greatly lower the risk of potential damage to the ship while she is being towed.
This option will require a significant initial investment for the construction of the dry dock and
the shelter, and installation of the dehumidification system. On the other hand, with the
implementation of the corrosion control measures (dehumidification, optimized underwater hull
cathodic protection system, weather-proof sheltering) it is foreseeable that the long-term
maintenance cost will be significantly reduced. In addition, with the ship available to public visit
all year round more revenue will be able to be generated, which can be used to subsidize the
maintenance expense.
6.6
Selection of Preferred Option
Among the five options presented in the report Option 1 can be ruled out as use of the current
maintenance practices will not be able to preserve the ship. Option 2 presents a number of
corrosion control measures that can significantly reduce the corrosion rate of the interior hull
structure and therefore can be used as a measure for the short term preservation.
For the berthing options presented in the report the floating berth options are the better options
than the dry berth options as the floating berth options will be able to provide the same or better
preservation of the ship than the dry berth options in terms of the corrosion issues. In addition, the
floating options will be able to maintain distributed load to the hull structure and, hence, be able
to minimize the possibility of the hull losing shape.
Among the two floating berth options, Option 5 is the preferred option as this option is not only
able to deliver the long-term preservation of the ship, but also able to allow full public access all
year round.
33
7
Recommendations and Future Work
7.1
Recommendations
The following recommendations are made based on the long-term and short-term preservation
plans:
1. For long-term preservation of HMCS SACKVILLE, it is recommended that a permanent
enclosed docking berth, as presented in Option 5, be adopted. This option will be able to
provide the best approach for the corrosion protection of both interior and exterior hull
structures. This option will also be able to allow public access to this historic ship all year
round.
2. Many corrosion control measures can be taken immediately before the long-term
preservation plan can be implemented. It is recommended that dehumidification and
coating applications, as described in Option 2, be adopted as a short-term preservation
plan for the interior hull spaces. Taking these corrosion control measures will
significantly slow down the corrosion processes and help to stabilize the interior hull
structures of the ship.
7.2
Future Work
The following future work has been recommended based on the short-term and long-term
preservation options:
1. The Secretary of the Interior's Standards for Historic Vessel Preservation Project with
Guideline for Applying the Standards published by U.S. Department of the Interior, Office of
the Secretary cover the guidelines for preservation of historic ships [35]. It is recommended
this standard be used as a Canadian reference standard when implementing the HMCS
SACKVILLE preservation project.
2. A HMCS SACKVILLE Preservation Project, as part of the effort to implement the short-term
preservation plan, be implemented as soon as can be arranged. This project should consist of
at least the following tasks:
1) Wet and dry hull survey.
A thorough examination of the ship hull should be conducted by a qualified hull
surveyor in order to determine the condition of the vessel and to plan for maintenance
and repair. The survey should focus on the corrosion damage to the hull structure, in
particular the damage to the hull plating and frames in the machinery spaces and in
all ballast tanks and fuel tanks. As it was already known that severe corrosion
occurred underneath the coatings in the interior hull plating below the water line, the
survey should be conducted to determine the condition of the hull after all coatings
34
are removed in according with appropriate coating removal procedure. The survey
results should include the thickness gauging of the hull plating and condition of the
rivets in the areas where severe corrosion was known to have taken place.
2) Maintenance and repair.
Repairing or, if necessary, replacing severely corroded, deteriorated structural
members or hull materials (e.g. frames and hull plates, rivets) with new material of
the similar composition, size, scale, and methods of fastening and construction to the
original.
3) Coating applications.
The existing coating applied on the interior plating already lost its function as a
physical barrier between the hull plating and moist environment. It is recommended
that all interior hull plating be recoated to regain its corrosion resistance as an
effective physical barrier. As discussed in Section 5.4 surface preparation,
temperature, temperature difference between a surface to be coated and the air around
it, humidity level, and coating thickness are all critical factors influencing coating
performance. It is recommended that the surface preparation and painting systems for
all interior hull plating be based on those specified in “Specifications for
Maintenance Painting of HMS Ships” [30]. Before the coating applications, all water
collected at the bottom of the bilge should be removed and sources of the leak should
be pinpointed and appropriate measures taken to stop the leak.
4) Dehumidification.
For large enclosed bilge spaces, such as engine room and boiler rooms, it is
recommended that a dehumidification system be installed to control the humidity
level of these spaces. The dehumidification system should have a monitoring, control
and feedback system so that the humidity level can be maintained at or below 40%
RH 90% of the time and below 50% RH all the time. To maximize the benefit of the
dehumidification system, air ducts should be installed to direct the dried air right to
the surface of the lower portion of the hull plating. Efforts also need to be made to
maintain the doors and hatches to these enclosed spaces closed and well sealed.
5) Use of scrap metals for ballast.
For all water ballast tanks and fuel tanks, it is recommended to empty, clean and
inspect those tanks, complete any structural repairs, and use scrap metal for ballast as
necessary. The advantage of using scrap metals is that metals do not absorb moisture.
It is also recommended that the dehumidification system be extended to these tanks.
Alternatively and if some tanks do not need to be used in the future, it is
recommended that a silica gel desiccant canister along with a humidity sensor be
installed in each tank and then reseal the tank. The silica gel desiccant can absorb
excess moisture in the tanks and effectively reduce the RH. This alternate method has
been used in the preservation of USS Missouri [36]. If the gel becomes oversaturated
with moisture it can be regenerated by heating it to 220°C, and the moisture is
35
released. However, regenerating the silica gel is not expected to be a routine
occurrence. Once the air is dry there should be no other source of moisture - unless
there is a leak in the hull and water seeps into the tank. This desiccation method can
also be applied to any other enclosed voids in the bilge.
6) Application of Corrosion Preventative Compounds.
For hard-to-reach areas in the bilges where coating applications cannot be carried out
or dehumidification system cannot be covered, Corrosion Preventative Compounds
(CPC) can be applied to control the corrosion of the hull plating in these areas. CPC
are fluids that are used in a temporary capacity to provide an extra layer of protection
for equipment, where the original protective coating has degraded [37]. CPC are
commonly hydrocarbon-based and vary from low viscosity liquids to hard waxy
solids. They can be classified by the type of film they develop after curing, i.e., hard,
waxy or oily. CPC are generally formulated with a corrosion inhibitor, a film former,
a solvent and sometimes a water displacing component. Some CPC act by spreading
across surfaces and into crevices, displacing any water which may be present. The
carrier solvent evaporates and leaves a residue consisting of the film, hydrophobic
additive and the inhibitors. Others dry to a waxy or hard resin like finish after
application and provide a barrier film. It should be remembered that CPC are
designed to give temporary corrosion protection and are not expected to perform as a
more permanent corrosion inhibiting coating might. Therefore, re-application of CPC
in the hard-to-reach areas is required on a periodic basis.
7) Redesign of underwater hull cathodic protection system.
The hull survey results in Section 3.2 have shown that the existing arrangement of the
zinc anodes resulted in overprotection of the underwater hull. It is recommended the
cathodic protection system be redesigned in order to provide optimal corrosion
protection of the wetted hull. As a historic ship that will be permanently afloat in the
dry dock for public visit, the zinc anodes can be suspended and equally distributed
along both sides of the ship. These anodes need to be electrically grounded to the hull
plating. This arrangement of sacrificial anodes has been used for the corrosion
protection of the wetted hull on HMS CAVALIAR. The advantages of this anode
layout are three folds: (1) The suspended anodes, as they are away from the hull
surface, will provide more uniform cathodic protection potential of the underwater
hull than the anodes bolted to the hull surface; (2) The anodes can be easily replaced
and number of anodes be easily adjusted; and (3) Surface preparation of and coating
application on the underwater hull can be easily carried out as there are no anodes
mounted on the hull.
8) Hull mounted silver/silver chloride reference electrodes.
It is also recommended that two silver/silver chloride (SSC) reference electrodes be
installed on the underwater hull surface, one in the forward part of the hull and one
on the aft part of the hull. The reference electrodes will be used to monitor the level
of cathodic protection on the underwater hull. DRDC Atlantic has developed the
capability of the numerical modelling of shipboard cathodic protection system [38]
36
and would be happy to provide support on the design of the cathodic protection
system.
3. Design and construct a permanent enclosed docking berth as part of the long-term
preservation plan.
It is recommended that a dry dock be constructed at the Halifax waterfront and be used as the
permanent enclosed docking berth site for HMCS SACKVILLE. It is also recommended that
a weather-proof shelter be constructed around the dry dock. The weather-proof shelter will
allow the public to visit the ship all year round. In addition, the dry dock should also be able
to facilitate the dry-docking of the ship for minor maintenance and emergency repair of the
ship. To meet this requirement, the dry dock should include a gate in order to keep the dry
dock water tight. The gate should also be able to be opened and closed to allow the ship to be
towed away for major maintenance. It is also recommended that the ship be kept afloat in
fresh water in order to eliminate marine growth on the underwater hull and to reduce the
corrosion damage to the hull in the splash zone. An appropriate pumping and circulating
system should also be installed to maintain a preset water level in the dry dock and to keep
the water attractive and savoury.
37
References .....
[1] HMCS SACKVILLE 1941-1985, Marc Milner, The Canadian Naval Memorial Trust,
Halifax, Nova Scotia 1998.
[2] Hull survey report for HMCS SACKVILLE, FMFCS Job No. 801057150, 24 April 2008.
[3] Hull survey report for HMCS SACKVILLE, FMFCS Job No. QHM08/09-12, 19 June 2008.
[4] Hull survey report for HMCS SACKVILLE, FMFCS Job No. 801056719, 14 April 2008.
[5] Hull survey report for HMCS SACKVILLE (#4 water ballast tank), FMFCS Job No. (no job
number available) 14 Dec 2008.
[6] http://www.hmscavalier.org.uk/specs3/index.html (25 November 2009)
[7] Private communication with Richard Holdsworth, Chatham Historic Dockyard Trust, 19
November 2009
[8] Private communication with Bob Daubeney, Portsmouth Historical Dockyard, 20 November
2009
[9] Lambert, Andrew (1987). Warrior: Restoring the World’s First Ironclad. Conway Maritime
Press.
[10] http://www.portsmouth.co.uk/gosport/Gosport-museum-set-to-kill.3206562.jp. (22 August
2010).
[11] http://www.schnorkel.blogspot.com/. (22 August 2010).
[12] Private communication with J.J. Molloy, The Royal Navy Submarine Museum, Gosport, 20
November 2009
[13] Watkinson, D., Tanner, M., Turner, R., and Lewis, M., 'ss Great Britain: Team work as a
platform for innovative conservation'. The conservator 29 (2005) 73-86.
[14] Cox, J. with Tanner, M. (1999). Conservation plan for the Great Western Steamship
Company Dockyard and the ss Great Britain. Volume 1. ss Great Britain Trust.
[15] Turner, R., Tanner, M. and Casey, S. (1999). Conservation plan for the Great Western
Steamship Company Dockyard and the ss Great Britain. Volume 2 – Condition report and
recommendations for the ss Great Britain. ss Great Britain Trust.
[16] Watkinson, D., and Lewis, M., ‘ss Great Britain iron hull: modeling corrosion to define
storage relative humidity’, in Metal 04 Proceedings of the International Conference on
Metals Conservation, ed. J. Ashton and D. Hallam, National Museum of Australia,
Canberra (2004).
38
[17] Watkinson, D., and ., Tanner, M., ss Great Britain: Conservation and Access - Synergy and
Cost, in Proceedings of the 2008 International Institute for Conservation Congress, London
(2008).
[18] Coe, T.E., Lawrence, and Davies, W.B., "Restoring Titanic's Little Sister, The SS
Nomadic", Proceedings of Historic Ships 2009, 19-20 November 2009, London, UK (7
pages).
[19] Martin, J. H. (2005), “Atmospheric corrosion suppression through controlled humidity
protection – an operational readiness and force multiplier”, Material Performance, Vol. 44
No.3, pp.38-42.
[20] Griffin, R. B., "Marine Atmosphere" Metal Handbook, 9th ed., Vol. 13, ASM International,
Metals Park, OH, 1987, pp.902-906.
[21] http://www.tutiempo.net/en/Climate/Shearwater/716010.htm (10 May 2010).
[22] http://met.forces.gc.ca/english/general/Halifax/ (accessed between 22 April 2010 and 21
June 2010).
[23] http://www2.mar.dfo-mpo.gc.ca/science/ocean/BedfordBasin/CTD_temperature.htm (10
August 2010)
[24] Roberge, P.R., Handbook of Corrosion Engineering (New York, NY: Marcel Dekker, Inc.,
1999), p. 68
[25] Australia Government Department of Defence: Defence Science and Technology
Organization (Online). DSTO Publication online.
http://dspace.dsto.defence.gov.au/dspace/handle/1947/2683 (20 August 2010)
[26] Smith, S., Aging aircraft Branch Overview, Presentations at US Army Corrosion Summit
2009, February 2009.
[27] C. Bowles, A. Sheetz, H. Hack and K.L. Vasanth, Evaluation of Vapor Phase Corrosion
Inhibitors and Dehumidification as Corrosion Control Methods for Advanced Double Hull
Naval Ships, Proceedings of Tri-Service Corrosion Conference, WRIGHTSVILLE
BEACH, NC, 17-21 November 1997.
[28] Logis-Tech Inc (online). Manassas, Virginia. www.Logis-tech.com (20 August 2010).
[29] Munters (Online). Sollentuna, Sweden. www.munters.com (20 August 2010).
[30] Specification for Maintenance Painting of HMC Ships, D-23-003-005/SF-002; Department
of National Defence, Chief of Defence Staff, Ottawa, Ontario, 2009
[31] http://www.shipsnostalgia.com/showthread.php?t=27823 (9 September 2010)
39
[32] Wenzel, J., “Diminishing Shipyard Resources" , Proceedings of Third International
Conference on the Technical Aspects of the Preservation of Historic Vessels, San
Francisco, California on April 20-23, 1997.
[33] Private communication with Andy Curran, The Imperial War Museum, London, UK, 25
May 2010.
[34] Waite, S.T., "The Pros & Cons of Permanently Dry-Docking Historic Vessels", Proceedings
of Third International Conference on the Technical Aspects of the Preservation of Historic
Vessels, San Francisco, California on April 20-23, 1997.
[35] The Secretary of the Interior's Standards for Historic Vessel Preservation Project with
Guideline for Applying the Standards, U.S. Department of the Interior, Office of the
Secretary, May 1990
[36] Larsen, K. R., "Historic Battleship is fortified against corrosion for decades to come",
Materials Performance 49(5), pp. 26-30, 2010
[37] www.corrosion-doctors.org/Inhibitors/CPCs.htm (1 September 2010).
[38] Wang Y., Brennan D.P., Porter J.F., and KarisAllen K.J., Evaluation of a shipboard ICCP
system using a boundary element code, Proceedings of the 2nd International Warship
Cathodic Protection Symposium, held February 20-22, 2003 (Shrivenham, Swindon, UK:
Royal Military College of Science, 2003).
40
List of symbols/abbreviations/acronyms/initialisms
CFB
Canadian Forces Base
CNMT
Canadian Naval Memorial Trust
CPC
Corrosion Preventative Compounds
DL(A)
Dockyard Laboratory (Atlantic)
DRDC
Defence Research & Development Canada
HMCS
Her Majesty Canadian Ship
HMS
Her Majesty Ship
RH
Relative humidity
RMS
Royal Mail Ship
ss
Steam ship
SSC
silver/silver chloride
USS
US Ship
UT
Ultrasonic thickness
41
42
Distribution list
Document No.: DRDC Atlantic TM 2010-104
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that the abstract of classified documents be unclassified. Each paragraph of the abstract shall begin with an indication of the security classification
of the information in the paragraph (unless the document itself is unclassified) represented as (S), (C), (R), or (U). It is not necessary to include
here abstracts in both official languages unless the text is bilingual.)
Defence R&D Canada - Atlantic was tasked to conduct an options study on the permanent
preservation of HMCS SACKVILLE. The main objectives were to evaluate options for the
preservation of HMCS SACKVILLE in a permanent site and to provide preliminary
recommendations for preservation options. A number of preservation options were evaluated,
including maintaining the Status Quo, corrosion control of interior hull structure, dry berth,
floating berth in seawater, and permanent enclosed docking berth. These options were evaluated
based on the information collected through literature review and site visits to the historic ships
in UK on which various preservation practices have been adopted. Among the options
evaluated, a permanent enclosed docking berth with weather-proof shelter was considered the
most appropriate for the preservation of HMCS SACKVILLE. This option will not only meet
the objective of preserving HMCS SACKVILLE in perpetuity, but also allow full public access
to the ship all year round without weather effect. In addition, measures that can be taken in the
short term to mitigate the corrosion damage to the interior hull structures were identified. Future
work based on the recommended preservation option was also recommended.
14. KEYWORDS, DESCRIPTORS or IDENTIFIERS (Technically meaningful terms or short phrases that characterize a document and could be
helpful in cataloguing the document. They should be selected so that no security classification is required. Identifiers, such as equipment model
designation, trade name, military project code name, geographic location may also be included. If possible keywords should be selected from a
published thesaurus, e.g. Thesaurus of Engineering and Scientific Terms (TEST) and that thesaurus identified. If it is not possible to select
indexing terms which are Unclassified, the classification of each should be indicated as with the title.)
HMCS SACKVILLE, preservation, corrosion, dehumidification, option study

Preservation of HMCS SACKVILLE

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