Ship resistance and development of broken channels

Contents
1
Introduction .............................................................................................................3
2
Method .......................................................................................................................4
3
Full scale measurements – m/s Emsmoon ....................................................5
3.1
3.2
Vessel particulars .................................................................................................................................................. 5
Measurement set-up ............................................................................................................................................ 6
4
Collected resistance measurements 2013/2014 ........................................7
4.1
4.2
Brash ice channel measurements .................................................................................................................. 7
Open water resistance reference measurements ................................................................................... 9
5
Collected ice measurements 2013/2014 .................................................... 10
6
References.............................................................................................................. 12
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1
Introduction
For efficient, redundant and not least safe winter navigation in the northern
Baltics the interaction between the Finnish-Swedish ice class, available ice
breaker assistance and current ice conditions are of great importance. During
the most severe winter months the strength and capability of the merchant
vessels needs to be adequate to ensure the maritime safety and low
environmental risks. However, in the beginning and end of the winter season
or during mild winters less ice strengthen and special purpose built vessels may
be better suited for efficient operation.
The ice class rule notations are based on an ice going performance criteria of 5
knots in a newly broken brash ice channel with various brash ice depths
depending on ice class notation. For the highest ice class; IA Super a
consolidated ice layer of 0.1m is added to the broken brash ice thickness.
To address the constant changing ice condition, have an efficient winter
navigational infrastructure and still ensure high safety the ice class restrictions
has been inferred and are used during the winters.
In connection with the current ice/weather conditions and traffic situation
different ice class restrictions are decided for different areas and ports.
The ice class restrictions thereby rely on the performance of merchant vessels
with a certain ice class to maintain high safety, low environmental risks and
efficient infrastructure. The correctness of the performance compared to ice
class notation are thus of great importance.
One cornerstone in the performance of ice strengthen vessels are, except from
hull form and sufficient displacement, the installed main engine output power.
The minimum power requirement of the Finnish-Swedish ice class rule is based
on needed power to overcome the added brash ice channel resistance in the
above mentioned channels. The added resistance is determined either through
calculations or through ice model tests.
During the last years the results from calculation of minimum output power
requirements and results from ice model testing have diverged and full scale
data compared to calculated and possibly model tests have been asked for.
Focus in this investigation is on added brash ice channel resistance.
Comparisons between full scale measurements and calculations are to be
made.
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2
Method
To gain more knowledge and investigate the added brash ice channel
resistance full scale measurements are collected and compared with the added
resistance equation of the rules, RCH. The equation is a function of vessel size,
hull shape, ice class and brash ice thickness.
The full scale measurements are performed in several different brash ice
thicknesses, ice conditions and ice qualities. The ice conditions, channel width,
thickness, passage frequency etc. are monitored and measured before the
vessel passes the reference channel where the resistance measurements are
collected.
The full scale total resistance is determined through propeller shaft torque
measurements followed by propeller thrust calculations. Added brash ice
channel resistance is isolated through calculation aided by open water
reference tests with the same corresponding speed as for the total resistance.
The measurements are compared and evaluated against calculated added
brash ice channel resistance, RCH, according to the Finnish-Swedish ice class
rules.
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3 Full scale measurements – m/s Emsmoon
Added brash ice channel resistance measurements have been collected in
cooperation with Ahlmark Lines on-board the general cargo vessel m/s
Emsmoon. The vessel represents very well an average vessel trading in the
northern part of the Baltics, both regarding size and ice class. This is also shown
in a previous research project [1] which included a traffic analysis.
Measurement equipment was installed on the vessel and as the vessel called
suitable ports on its regular route in the north of Sweden measurements was
collected. A certain part of the port approach channel was chosen, ice
conditions were measured and the vessel reduced its speed to about 5 knots
during passage of the controlled part.
3.1
Vessel particulars
Table 1 - General information and principal dimensions m/s Emsmoon
General information
Principal Dimensions
Type
Built:
IMO
Call sign
Flag
Built
Classification
DWT all told
DWT cargo capacity
Loa
Beam
Draft
GT/NT
Speed
General cargo carrier
2000
9213894
V2BN3
AG
2000
BV I3/3/E, ice class 1A
6250 t
6000 t
111.74 m
14.95 m
6.38 m summer
4563/2613
Abt. 14 knots
Figure 1 - Reference vessel m/s Emsmoon
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3.2
Measurement set-up
The full scale measurements were collected with the SSPA in house data
collecting system. Measured and stored variables are listed in Table 2 below.
Table 2 - Measured variables in the datalogger system.
Variable
Unit
Comment
Latitude
Longitude
Speed over ground, SOG
Course over ground, COG
Heading, HDG
Rudder angle
Propeller pitch
Propeller rpm
deg, min
deg, min
knots
deg
deg
deg
%
min-1
Torque, Propeller shaft
kNm
Power, Propeller shaft
kW
Calculated
Pitch motions
Roll motions
Deg
deg
Positive bow-up
Positive to port
Positive to port
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4
Collected resistance measurements 2013/2014
In this chapter collected measurements during the mild winter of 2013/2014 is
briefly presented. Complete analysis of the measurements will be presented in
the final report of the project.
4.1
Brash ice channel measurements
Unfortunately only one measurement point in very light ice conditions was
collected. An attempted was made to include a second point however the ice
conditions was judged to be too light.
The measurement point was collected during departure, in ballast condition,
from Haraholmen the 26th of February 2014. Time series and pictures are
presented below. Presentation of corresponding ice conditions are found in
chapter 5.
Figure 2 Measurement area close to Haraholmen, Piteå.
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6.5
40
6
35
5.5
30
5
25
4.5
Speed [kn]
Shaft Torque [kNm]
Brash ice channel, Haraholmen 2014-02-26
45
20
0
100
200
300
400
500
4
600
Time [s]
Figure 3 Measured propeller shaft torque and speed over ground.
Table 3 Average figures, Haraholmen.
Average torque
32.5 [kNm]
Average speed
5.3 [kn]
Figure 4 Visualisation of channel, aft of vessel.
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4.2
Open water reference measurements
To be able to calculate the resistance component associated with brash ice
channel resistance (RCH) from the ice resistance measurements, e.g. presented
in 4.1, open water reference measurements are needed. The goal was to
collect speed-power curves in calm and deep water for both loaded and ballast
condition. During 2013/2014 the ballast condition reference was collected
which is presented below.
Open water reference 2014-04-05
80
Shaft Torque [kNm]
70
60
50
40
30
20
2
4
6
8
10
12
Speed [kn]
Figure 5 Propeller shaft torque vs. speed over ground.
Table 4 Measured open water torque.
SOGavg. [kn]
Torqueavg. [kNm]
1.2
13.2
1.3
15.1
3.9
17.7
7.8
29.9
10.3
47.3
13.0
75.1
13.5
88.1
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5
Collected ice measurements 2013/2014
The project aim is to monitor and analyse the growth and fate of a specific
approach channel during the winter season.
In 2013/2014 a weather station and a web camera were installed on the
northern shore of Skelleftehamn harbour. The first entrance of m/s Emsmoon
to Skelleftehamn in thin ice was video filmed on January 31 st. However the ice
melted and moved out from the harbour area on February 18 th. Despite some
cold spells in March only drifting floes were observed for the rest of the winter.
A picture from the web camera 2014-02-25 is shown in Figure 6.
Figure 6 Ice conditions in Skelleftehamn 2014-02-25.
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5.1
Ice conditions Haraholmen 2014-02-25
Ice measurements corresponding to the ship resistance measurement
described in section 4.1 is presented below.
Measurement of ice conditions in the ship channel south of Haraholmen.
Level ice on both sides of the
ship channel could be classified
as columnar ice with a
thickness of 45-50 cm. The
crystal bonds were partly
melted and the upper surface
was covered with 5-10 cm
snow and hard slush, see
Figure 7 (left).
Table 5 Position, time and temperature.
Position:
65°10.6 N, 021°36.0 E
Time:
2014-02-25, 12.00-13.30
Temp:
+4°C, sunny, light wind
The broken channel was about 30 m wide with a straight interface between
loosely floating ice blocks and the level ice. Typically the ice blocks were
rounded with 40 cm depth and 40-60 cm width. In average the depth was 40
cm along the center line with a gradually increasing depth to 80-110 cm along
the edges. The largest ice blocks were 100-150 cm in diameter measured at the
waterline with a depth of 90 cm. The channel was covered by 20 cm drift snow
that was mixed with ice and water when the channel was broken. Ice
distribution behind m/s Valkyria in the measured section as well as the chosen
measuring section of the ship channel as in section 4.1 is shown in Figure 7
(right).
Figure 7 Left:Vertical edge of the landfast ice outside Haraholmen.
Right: Ice block distribution behind tug boat Valkyria.
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6
References
1. Westerberg, 2014: EEDI and Finnish-Swedish ice class rules, Impact
study and operational aspects, SSPA Report RE40136554-01-00-B.
2. Trafiksäkerhetsverket, 2010. Isklassföreskrifter och tillämpning av dem.
Sjötrafikföreskrift, TRAFI/31298/03.04.01.00/2010.
Trafiksäkerhetsverket, Helsingfors. (Authors comment, i.e. FinnishSwedish Ice class rules)
3. Krav på isklass och tonnagestorlek, 2013,
http://www.sjofartsverket.se/sv/Sjofart/Isbrytning/Isklasser--krav/
Authors comment: General ice class restrictions, downloaded 2013-09.
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