1. Exploring the physics of ship design
Ship-Shape!
Exploring the physics of ship design
Ship-Shape!
Exploring the physics of ship design

2. Session outline: The social and economic benefits of shipping
How ships are designed
How to test if your ship is
doing its job
Design and build your very
own ship!
This slideshow is designed to apply principles of stability, buoyancy and water resistance to a practical design and make shipping exercise.
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From bananas to cars, trains to televisions – we will learn how this shipping industry is of importance to us all
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We will then look into how ships are designed – considering principles of stability, buoyancy and resistance
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Finally we will look at how to test if a ship is doing its job using a really simple equation and then apply all the theory learned in this presentation to a practical ship design and build exercise!

3. The Benefits: Shipping in our everyday lives
Employs 250,000 in the UK
Generates £37 billion to UK economy per year
The fishing industry provides us with a good source of protein for
our diets
Cargo shipping provides us with 95% of the products we use on a
day-to-day basis
Shipping is of importance to us all
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In the UK in particular, shipping employs 250,000 people in the UK,
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and is the second biggest earning industry after agriculture generating a massive £37 billion to the UK economy per year, that’s £162 per second (shown in the did you know box).
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As well as economic benefits, the shipping industry also provides social benefits as well, including a source of protein in our diets
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and the delivery of over 95% of the products we use on a day-to-day basis right to our doorsteps!
The ability of ships to perform their tasks depends a lot on the design of the ships themselves.
British shipping earns the UK economy £162 per second!*
*SeaVision UK
Did you know?

4. How ships are designed Considering the shape of ships
When naval architects and marine engineers design
and build ships, they have to follow a certain number
of rules…
Two of the most important are:
1 They have to float and stay upright – Looks at Buoyancy and Stability of ships
2 They have to be able to move – Looks at Power (thrust) and Drag on ships
Read through text
Click one – read through text
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Lets address each in turn…

5. 1 - Buoyancy and Stability
Keeping afloat
When forces are balanced: Ships float
Lower density - greater buoyancy
due to higher displacement of
surrounding water – Archimedes
Stability
Staying upright
Greater buoyancy – less stable
Requires a low centre of gravity
Weight
Upthrust
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In relation to buoyancy
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when forces are balanced ships float.
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This is because the downwards force (weight) of the ship is balanced by the upwards force (up thrust) of the water. To link it back to Archimedes principle the weight of the water being displaced is the same as the weight of the ship.
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In relation to stability however
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Having greater buoyancy is not necessarily a good thing for ships as this means ships are less stable in the water and during sailing, potentially resulting in what is being shown here.
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To compensate for this ships often have a low centre of gravity to keep stable.
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To understand centres of gravity lets take a look at these two characters. Which one do you think is most stable? The one on the left with a large head and small feet, or the one on the right with a normal sized head and large feet?
Why?
The one on the right is more stable because it has a lower centre of gravity. Ships use similar principles, particularly cargo ships when loading products to ship around the world.

6. 2 - Power (thrust ) and Drag
When forces are balanced: ships are stationary
Thrust Force = Drag Force
However,
Ship’s engines must provide enough power (thrust) to overcome drag (water resistance, which is a form of friction) so that:
Thrust Force > Drag Force
So that ship’s can move
through the water and
transport cargo from A to B!
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When forces are balanced ships are stationary
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i.e. the thrust force (provided by the engines of the ship through the combustion of fossil fuels) is equal to the drag force on the ship (provided by water resistance)
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However, ship’s engines need to provide enough power (thrust) to overcome drag so that the thrust force is greater than the drag force
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And ships can move from A to B!

7. Generating thrust on a ship
HEAT
Fuel
Engine
Combustion
Oxygen
For a bit of background, thrust is generated in ships through the combustion of fuel (often diesel oil) with oxygen in the engine. This provides work done which drives a propeller to generate forward motion. The process also generates waste heat energy and emissions.
The efficiency of shipping in terms of buoyancy, stability, resistance and drag has a lot to do with ship shape!
(More information on the impacts of emissions from ships can been seem in Shipping and Climate Change in Module C) from the Inspiring Seas website).
HC’s + O2  CO2 + H20
Work done

8. The Shape of Ships Buoyancy and Stability
How stable and buoyant a ship is has a lot to do with its shape:
Depth of cargo hold
Surface area in
contact with water
Vs.
Deep
Shallow
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The depth of the cargo hold can effect how stable a ship is in the water
Ask pupils why they think this is:
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Ask which type of cargo hold (deep or shallow) is likely to provide the most stable design in the water. The answer is ‘deep’ because it has a low centre of gravity and is therefore more stable (remind of the stickmen drawings)
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The surface area in contact with the water can effect a ships performance
Ask pupils why they think this is. Emphasise it has something to do with resistance
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Ask which type of cargo hold is likely to produce least resistance in the water – They should choose ‘low’ because a lower surface area of the ship is in contact with water and therefore a lower resistance is generated on the ship.
However, now ask pupils which of the ships is likely to be more stable in the water. They should say ‘high’ because being lower down in the water increases stability because it lowers the centre of gravity. However, in this case ships also need to be very careful that the ship does not sit too low in the water otherwise it may fill with water and sink!
Emphasise to pupils that there is a trade-off between resistance and stability and that ships in particular need to be very careful about getting this calculation right, otherwise it could endanger the life of the crew (if the ship is unstable) or make shipping an inefficient method of transport (if resistance on the ship is too high).
This is an important lesson to remember when designing and testing your ships!
Low
High
Vs.

9. The Shape of Ships Resistance and drag
How resistant to drag a ship is has a lot to do with its shape:
Streamlining
Surface texture
Vs.
Curved
Straight edged
The drag on a ship has a lot to do with its shape.
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Which of these shapes do you think would provide the most streamlined design for ships? Ask pupils why
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Which of these surface textures do you think would provide the most streamlined design for ships? Ask pupils why
For more information about how marine engineers keep ships’ hulls smooth during sailing, please see Paint_Science in Module C) Shipping and the Environment available from the Inspiring Seas website
Vs.
Smooth
Rough

10. …but how do we test this efficiency?
So shape clearly has an influence over how good, or efficient a ship is
Now we understand that how good, or efficient, a ship is has a lot to do with its shape, but how do we test this efficiency practically?
…but how do we test this efficiency?

11. How to test if your ship is doing its job: a really simple equation
How good (efficient) a ship is at doing its job can be measured by
the amount of cargo carried per unit fuel, using the really simple
equation:
Efficiency = Weight of cargo carried (g)
Units of fuel used (money)
Read text
But why efficiency so important to the shipping industry?!

12. …because it makes them more:
Cost effective: A streamlined shape lowers drag and the
amount of fuel needed to provide the power (thrust) to
move ships from A to B.
Environmentally friendly: lowering the amount of fuel
needed to transport ships from A to B means less
pollution to the atmosphere and surrounding
water.
Ask pupils what their ideas are:
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First of all an efficient design makes shipping a more cost effective industry. If ships have a streamlined design for example less water resistance is imposed on the ships hull. This reduces the power (thrust) required to overcome resistance and so less fuel is required to move ships from A to B. This means for cargo shipping for example the end products (bought by us the consumers) are actually cheaper to buy because it cost less to get them to us!
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Not only this but by reducing the amount of fuel required to power ships we also make shipping a more environmentally friendly industry as less pollution is generated in the form of oil pollution and emissions.
Ask pupils what the effects of fossil fuel emissions are (looking for acids in the environment and global climate change). More information on shipping and the environment can be found in Module C) from the Inspiring Seas site.

13. Design, build and test your very own ship! The design and build
Step 1 – Using your marker pen, draw as accurately as possible a 3D outline of a ship onto your block of foam
FRONT (bow)
BACK (Stern)
Step 2 – Cut out your ship shape using the hack saws and safety rulers provided
Click one two and three for the three steps
Ask pupils why they think its important for the cargo hold to be fairly deep? – Looking for comments on buoyancy and centre of gravity
Ask pupils why they think it is especially important for their ships to be smooth on the outside? – Looking for comments about streamlining in the water to reduce resistance.
Step 3 – To make your cargo hold, draw a box using your marker pen and score around it using a Stanley knife and safety ruler. Score across the box too. Using a flathead screwdriver, tease the pieces of foam out until you have a cargo hold. Sand the whole design down to a smooth finish and decorate using waterproof marker pens.

14. Some examples of previously designed ships
These are some ships previously designed using this activity.
Yours should looks something like this.

15. Design, build and test your very own ship! The test
Stability – Does it float and does it stay upright?
Stability testing tank
The first thing you will need to do with your model ships is to test them for stability. Put your ships in a tray of freshwater. Do they float? Why do you think this is? Use the principal of Archimedes.
Now load your ship up with cargo. You can put in as much as you like but bare in mind your ship still needs to float and stay upright to be tested during the next stage of the practical! Don’t forget we are not trying to carry the most cargo possible, we are trying to get a balance between cargo carried and the amount of fuel that is needed to generate thrust to carry the cargo. Today we will be symbolising this fuel to generate thrust as units of money.
Once you have decided how much cargo you are going to use keep it inside the ship for the next stage.

16. Design, build and test your very own ship! The test
Resistance – How much cargo (metal nuts) can your ship carry for the lowest amount of fuel (money)
Bow line (fair test)
Towing point (screw)
Towing line (cotton thread)
Here is the set up you will compete against your classmates in! This tests the resistance of your ship. From here we get a value of efficiency for your ship!
Your ship will be placed in a container full of flowing water known as a towing tank. Your ship will be loaded with cargo (the amount you decided on) with a small screw attached to the front (bow) of your ship known as a tow line. A piece of cotton will be tied to the tow line which in turn is attached to a small plastic bag to hold the number of coins (we suggest using washers) it takes to drag your ship against resistance (a flow of water) to overcome this force and generate forward motion. The experiment is over when your ship starts to move forward against resistance. Count the number of pennies it took for the g of cargo you held.
Why do you think we need to line all the ships up at the same point in the towing tank? – the bow line
How else could we make sure this experiment was a fair test?
Always use the same flow rate
Always have the same person deciding when forward motion has occurred and each ship has overcome the force of resistance
Water flow
(small bag)
(washers)
Rubber tubing (Attached to a fast running tap to generate flow)
Water exit hole (To keep flow maintained)
i.e. how efficient is it!?

17. Physics in the real world: Exactly how its done in the business!
The technique pupils will be using to test their ship designs for resistance is actually used in the business to test the resistance of actual ships and is known as a towing tank.
When ships are commissioned and designed by Naval Architects, a hugely scaled down version is made from wood, wax or fibre glass and is tested for efficiency in a piece of equipment known in the business as a ‘towing tank’.
The tank has a run line for the model ship to be attached to, which then draws the ship through the water. The resistance on the ship model can be measured and with some careful maths marine engineers can work out whether the ship, when built to full size and out of steel, would be seaworthy. That’s some pretty important physics!
Newcastle University’s Towing Tank

18. Physics in the real world: Your experiment
Efficiency = Weight of cargo carried
Units of fuel used (money)
For this exercise we can find out who’s ship is most efficient by working out who can carry the most cargo (metal nuts) for the least amount of thrust generated by fuel consumption (the pulley system weighed down with washers – symbolising money spent on fuel). The pulley system attached to the ship needs to be loaded down with washers until the ship moves against the water current (symbolising drag on a ship) and in a forwards direction.
The amount of cargo carried (weigh the metal nuts in g) can then be divided by the money required to provide forward motion on your ships (number of washers) to give you efficiency which is a value of g/unit money.

19. (Weight of cargo / amount of coins (money)
Results
Team name
Weight of cargo
(g)
Fuel (money) required
(Number of coins)
Efficiency of ship
(Weight of cargo / amount of coins (money)
1 -
2 -
3 -
4 -
Make sure pupils give their ships and teams a name.
You may want to run this as a competition and hand out a small prize.