Seamanship Station - Inland Seas Education Association

XIV. SEAMANSHIP STATION
INTRODUCTION
Seamanship “is the whole area of taking a ship from
one place to another. It is that department of a ship’s
being which is concerned with the rest of the daily
management of the ship, her gear, her boats, anchors,
and cables, rigging...watch kept at sea and in harbor.”
(Taken from the Oxford Companion to Ships & the
Sea)
The Seamanship Station offers students an
opportunity to steer the boat, to learn how the wind
and sails interact to make the boat move, and to learn
how to use the boat’s compass. Students will learn
about schooners and their importance to the maritime
history of Grand Traverse Bay.
The Seamanship Station is a good time to help the students place the schooners in an historical
perspective – while Inland Seas was built in 1994 and Manitou was built in 1982, they were both built to
look like and work like a traditional schooner from the 1800’s.
LEARNING OBJECTIVES
Students will be able to:
1. Steer the ship and respond correctly to steering commands from the captain.
2. Explain why a ship floats (buoyancy and displacement).
3. Explain how sails propel the ship.
4. Describe the purpose of the keel and how the wheel and rudder steer the ship.
5. Describe mechanical advantage in terms of the main sheet and wheel.
6. Describe the basic operation of the ship’s compass.
7. Place the schooner in historical perspective (age of sail on the Great Lakes, cargo carried,
economics).
8. Explain the role of ballast water to the introduction of invasive species in the Great Lakes and
provide three examples.
TOOLS
5-gallon bucket
Digital camera
Hull material (steel)
Piece of lead
Plastic pan
Rechargeable batteries & charger
Sail material (dacron, cotton)
Seamanship Station manual
Taconite
TEACHING THE STATION
Before sailing, discuss the Seamanship Station with the Captain to see how he or she wants to handle it.
The Seamanship Station is usually taught as a team with the Captain. However, the Seamanship Station
instructor is expected to take the lead in teaching the station and should be prepared to teach the entire
station if the Captain is occupied by the weather, etc.
Assemble the student group near the helm, without blocking the captain’s vision. The Captain will assign
two students to the helm and explain the steering commands. Change the two students at the wheel every
two to three minutes so everyone gets a chance to steer. Be sure to keep the students at the wheel
involved in your lesson as well.
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Ask the students if they know how a ship floats. Demonstrate the concept of buoyancy using the steel
hull material. Fill the 5-gallon bucket with water. Ask the students if the steel plate with float or sink if
placed in the bucket of water, then place the steel plate in the bucket. Why did the steel plate sink? What
can be done to make the steel plate float? Demonstrate the concept of displacement by placing the steel
plate in the plastic pan, then placing the pan in the bucket of water. Does the steel plate float? Discuss
the results.
Explaining how sails propel the ship can be complicated. It is important to take into consideration the
age-level and background of the students. For elementary and middle school students, simply discuss
how the wind is a force acting on the sails, causing the ship to move. For high school students, discuss
how sail lift is a combination of Bernoulli’s Principle and Newton’s Second and Third Laws. For all
students, discuss the purpose of the keel in terms of how it keeps the ship from being pushed sideways
by the wind and how it helps resist heeling (leaning to one side).
Ask the students how the ship is steered. Discuss the operation of the wheel and rudder. This is a good
time to demonstrate mechanical advantage using the main sheet and wheel. Mechanical advantage can be
shown by having the students count the number of parts the main sheet is divided into by the blocks.
Students can also calculate the mechanical advantage of the ship’s wheel using the ratio of effort
distance to resistance distance.
Stewardship Component
When discussing the keel and the displacement of the vessel, it is a good time to introduce the concept of
ballast, the weight (usually in the form of water) that is added to the boat to make her more stable. Most
cargo vessels use water, which has many organisms living in it. When this water is dumped into a new
aquatic system (i.e. the Great Lakes) these introduced organisms can invade and alter the Great Lakes
ecosystem. Examples of such organisms are the spiny water flea, the fishhook water flea, round goby,
zebra mussels, and quagga mussels.
Have the students imagine themselves on a schooner in the late 1800s. How are they able to navigate?
Show the students the compass and briefly discuss its operation. Use the rest of the time to discuss the
history of schooners on the Great Lakes.
DATA COLLECTION
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VOCABULARY
Ballast: weight carried in the bottom of the keel to resist heeling (leaning to one side).
Buoyancy: upward force that enables an object to float.
Displacement: volume or weight of water displaced (moved aside) by a floating ship. The weight of the
water displaced equals the total weight of the ship.
Drag: force that resists a solid (i.e.; keel, sail, or wing) moving through a fluid (water or air). This force
is parallel to the water or wind current.
Energy: capacity to do work.
Helm: another name for the steering wheel.
Hull: body of a ship.
Lift: force generated by a solid (i.e.; keel, sail, or wing) moving through a fluid (water or air). This force
is perpendicular to the water or wind current.
Keel: fin-like structure at the bottom of the hull that runs fore and aft. The keel keeps the ship from
being pushed sideways from the wind and helps resist heeling (leaning to one side).
Mechanical advantage: the benefit gained by using simple machines. Mechanical advantage is
calculated as the ratio of effort distance to resistance distance.
Rudder: fin-like device used to steer the ship. It is located underwater at the stern of the ship.
Schooner: fore and aft rigged vessel having at least two masts.
BACKGROUND INFORMATION
Buoyancy
Ask the students how the ship floats. Some students might think the ship is made of wood, and since
wood floats so does the ship. However, both of the schooners used for the Schoolship Program are made
of steel, and some ships were even made of concrete during a steel shortage at the end of World War I.
Floating depends of two things: displacement and density. Archimedes’ principle (which explains the
concept of buoyancy) states that for an object to float, it must displace an amount of water equal to its
weight. As the weight of a ship pushes downward and displaces water beneath it, an upward force equal
to that weight holds the ship up. This upward force is called buoyancy.
A ship must have an average density less than water to remain afloat without becoming submerged. The
shape and amount of open space (air) on a ship is the key. Imagine taking a ball of clay and tossing it into
the water – it would sink to the bottom. Now shape that clay like the hull of a ship so that its volume is
increased. This time, the ship will float on the surface of the water.
An object is said to have positive buoyancy when it floats, and negative buoyancy when it sinks. Imagine
placing a beach ball and a bowling ball in the water. A beach ball has positive buoyancy and will float,
while a bowling ball has negative buoyancy and will sink.
Sails Propel the Ship
Sailing a boat is simple when you are heading with the wind at your back. Simply let out your sails
perpendicular to the wind to capture the most energy. As the wind presses against the sails, the force
propels the sailboat forward. Trying to sail with the wind at your face is much more difficult. Sailing
directly into the wind will either push the boat backward (if the sails are let out) or it will stall the boat if
the sails are pulled in. Therefore, a sailboat must take a back and forth path (known as tacking) when
trying to sail upwind, so the wind approaches at an angle instead of head-on.
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When sailing upwind, the boat is actually being pulled by the force of the wind, rather than being pushed
like when you are sailing downwind. This pull is known as lift. There are two common ways to help
describe how the wind interaction with the sails helps to generate lift and cause the boat to move:
Bernoulli’s Principle and Newton’s Second Law.
Bernoulli’s Principle
Bernoulli’s Principle explains lift in terms of the difference in pressure. Imagine the bow of the boat
angled upwind. As the wind hits a sail, the air particles rush over both sides of the sail. Air particles
traveling across the outer (convex) side of the sail have a longer distance to travel in the same amount of
time as the particles moving across the inner (concave) side of the sail. Therefore, the air particles on the
outside of the sail have a faster speed (or higher velocity) and have more room to spread out, forming a
low-pressure area. The air particles on the inside of the sail have a slower speed and are packed together
more tightly, creating a high-pressure area. The pressure difference on the sails produces lift and causes
the sailboat to move. The lift force is directed roughly at a right angle to the curved portion of the sail.
Actual measurements of the pressure differences on sails have revealed the measured lift in much greater
than Bernoulli’s Principle predicts. Therefore, there is more to the story.
Newton’s Second Law
Newton’s Second Law describes lift as the force produced by a change in the wind’s direction by the
sails. The formula for Newton’s Second Law is:
Force = Mass x Acceleration
Acceleration is a function of magnitude (speed) and direction. Changing either the speed or direction of a
flow (such as the wind) generates a force. Therefore, slightly changing the direction of the wind by
pulling in the sail (filling the sail with wind) creates lift.
Keel
The keel is essential in the forward movement and stability of a sailboat. The keel runs fore and aft along
the bottom of the hull and keeps the boat from being pushed sideways by the wind. The keel also
contributes to the stability of s ship since the ballast is held in the bottom of the keel. The weight of the
ballast counteracts the heeling motion created by force of the wind on the sails and keeps the ship from
tipping over. Inland Seas has a fixed keel with 20,000 pounds of lead ballast, while Manitou has a fixed
keel as well as a moveable centerboard.
Wheel & Rudder
The wheel and rudder are used to steer the sailboat. The wheel is connected to the rudder, located
underwater at the stern of the ship. When the wheel is turned, the rudder turns in the same direction. The
rudder cannot be turned more than 35o on either side of the centerline. If the rudder was turned at a
greater angle, the rudder would stall and lose its grip on the water (creating more drag but no more
turning force).
Mechanical Advantage
Mechanical advantage is the benefit gained by using simple machines. The formula for mechanical
advantage is:
Mechanical Advantage = __Effort Distance_
Resistance Distance
Mechanical advantage is used often on sailing vessels, including the ship’s wheel and axle and the tackle
in adjustment systems such as the main and fore sheets. The wheel and axle is a simple machine
consisting of a large wheel rigidly secured to a smaller wheel or shaft, called an axle. When either the
wheel or axle turns, the other part also turns. One full revolution of either part causes one full revolution
of the other part. On Inland Seas, the mechanical advantage of the wheel and axle is the ratio of the
radius of the wheel (effort distance; 24 inches) to the radius of the axle (resistance distance; 1/2 inch).
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Since the radius of the wheel is 48 times larger than the radius of the axle, the mechanical advantage is
48:1.
To determine the tackle’s mechanical advantage, count the number of short line lengths in the tackle, or
the number of times the line goes over a moveable block. For example, two blocks that divide the line
into three parts have a mechanical advantage of 3:1. This lets you pull 90 pounds with 30 pounds of
effort, but requires pulling three times the length of line. On Inland Seas, the mechanical advantage of
the main sheet is 7:1, while on Manitou it is 5:1. The mechanical advantage of the fore sheet is 4:1 on
both schooners. Diagrams describing the ship’s wheel and main and fore sheet mechanical advantage can
be found in the Seamanship Station manual (and on page 173 of this manual).
Compass
The original compass probably consisted of a magnetized needle stuck in a straw or cork, floating in a
basin of water. The needle would point to magnetic north. Lodestone (leidarstein) may have been used as
a primitive compass by Norsemen as early as 868 AD. The compass first appeared on Chinese ships
about 1111 AD, and was found in the Mediterranean shortly thereafter. The compass was the principle
navigation instrument used by Columbus, who noted the effect of variation although he did not know the
cause. The first chart with isogonic lines (lines of equal variation) was produced by Halley in 1701.
Deviation was discovered by Matthew Flinders in the early 19th century.
Variation is the difference between the bearing to the magnetic north pole and the true (geographic)
North Pole, expressed in degrees East or West. Variation is not constant at any location, because the
magnetic field of Earth is always changing. The variation for any area and the rate of change is shown on
a chart’s compass rose (shown below).
Magnetic disturbance caused by ferrous (iron) metal objects or electronic current aboard a ship that
results in errors to the compass is known as deviation. This concept can be easily demonstrated by
running something metal (such as a pocket knife) near a hand-held compass. These errors can be largely
eliminated by careful compass adjustments (using the two large metal balls on either side of the ship’s
compass and small internal magnets). Deviation varies with the ship’s course.
Historical Perspective
Refer to Section II, the “History & Facts of the Great Lakes” (pages 63-68) of this manual.
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REFERENCES
Karamanski, T. 2000. Schooner Passage. Wayne State University Press, Detroit.
Kemp, Peter, ed. 1976. Oxford Companion to Ships & the Sea. Oxford University Press, London.
Maloney, E. 991. Chapman Piloting, Seamanship and Small Boat Handling. Hearst Marine Books, New
York, NY.
Seidman, D. 1994. The Complete Sailor. International Marine, Camden, ME.
Smith, H. G. 1971. The Marlinspike Sailor. International Marine, Camden, ME.
Smith, H.G. 1990. The Arts of the Sailor. Dover Publications, New York, NY.
Internet Sites of Interest
http://www.sailtraining.org (American Sail Training Association)
http://boatnerd.com/ (Great Lakes and seaway shipping)
http://www.uark.edu/depts/aeedhp/agscience/simpmach.htm (mechanical advantage)
DIAGRAMS & RELEVANT DATA
Sail names (page 157)
What makes a schooner a schooner? (page 158-159)
Ship’s wheel mechanical advantage (page 160)
Main and fore sheet mechanical advantage (page 161)
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Resistance Distance (R) =Radius of Shaft ½“
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