UP ON THE FOILS

Learning Intention:

 

To learn how sailing boats have changed over time and how the materials used have evolved with new technologies

The untold story of foiling? Thanks to Emirates Team New Zealand for the video

Discussion:

 

Why have sailboats changed over time?  What do you wonder about how sailing started?

For thousands of years people have been harnessing the power of the wind to sail across the oceans. Over time the shapes and technologies of sailing boats have changed. 

 

What are the differences between the waka sailed to New Zealand many years ago and the America's Cup boats of today?

  

Hull shapes have changed.  That is the main body of the boat. The hull has changed to reduce drag in the water.  Materials used have become lighter and stronger, increasing the speed of boats.  

Initially boat hulls would have been a floating log used to get across a river or out to an island.  The next innovation was to hollow out the middle and sit in the hollowed out part, keeping the crew dry. 

 

The first settlers arrived in Aotearoa in waka from Polynesia. The waka were large enough to carry many people and their food. The waka were double-hulled, like two canoes side by side. 

 

What do you think they were made from?

 

The waka were built from tree trunks. 

 

What do you think was the advantage of two hulls? 

 

In Polynesia waka were narrow and not very stable, because they were carved from narrow trees, so having a double hull made them steadier.  

Boat designers changed the shapes of the boats and also the materials that they were built from, to make them go faster.

How have sails changed over time? 

 

Pacific voyagers used wind to sail their waka to Aotearoa.  What were their sails were made from. 

 

Raupo (a reed) or flax harakeke were used. 

 

As technology improved over the years, sail materials have changed, from natural fabrics such as cotton, to polyester, kevlar and carbon fibre.  Sail shape is also continually being developed.  During the last America's Cup the boats used a wing-sail made from rigid plastic that needed a crane to attach it to the hull, each time it went sailing.  On an America’s Cup boat today they are using a double skinned soft wing-sail. This aerofoil shape makes them perform better than a single layer sail.  

The boats that will compete in the next America's Cup regatta are built using Carbon fibre  which makes them lighter than ever before. It is this advancement which allows them to be light enough to be lifted out of the water on foils so they look like they are flying.

 

What do you know about these foils or foiling? 

 

A foil, when we are talking about sailing or flying is basically a wing that generates lift.  Lift is a force that pushes something up. A wing is called an aerofoil if it operates in the air and a hydrofoil if it operates in the water.  The foils on sailboats are attached to the hull or keel.

 

How does the foil create lift? 

 

Foils create lift when air or water travelling over the top surface of the foil goes faster than the air or water travelling over the bottom. This happens because the top of the foil is either curved or angled.

A hydrofoil can lift its hull out of the water.  When it moves quickly the special foil wings that are under the water allow it to fly. This means there is less drag in the water to slow the boat down and they can travel very fast. The latest America’s Cup boats are hydrofoils.  They travel over 75km/h. 

Activity:  Making an aerofoil or wing to demonstrate lift.

 

Materials:

  • Paper - slightly stiff is best

  • Scissors

  • Sellotape

  • String

  • Straws

  • Pencil

  • Hair Dryer

 

Procedure:

 

  1. Cut a piece of paper to measure 18 x 10 cm.

  2. Fold it in half leaving a 1 cm overlap.

  3. Now make the overlapping ends meet together, which will make one side of the paper curved. 

  4. Tape the ends together.

  5. Make a mark 5 cm along the folded edge and 3 cm in from the front of the wing.

  6. Make 2 holes at the mark through the middle of the wing, top and bottom, with a pencil or scissors.

  7. Cut the straw to 7 cm and carefully poke through both holes. Tape in place. The straw will be slightly angled so the back of the wing will tilt down.

  8. Make a stabiliser for the wing to stop it from spinning.  Cut a shape out of paper like a tail on an aeroplane, approximately 4 x 4 cm and tape across the top centre back of the wing.

  9. Thread a long piece of string through the straw.

  10. Fix one end of the string to a high point such as a table top and the other end pull tight, straight down and put a heavy item on it, such as a book or ask someone to hold it tight.

  11. The wing should be able to slide up and down on the string.

 

Now it is ready to fly!

 

Lift the wing up slightly and aim the hair dryer, (on cold), at the folded edge, so the air travels over the top of the wing. Try not to blow the wing from underneath as this is not showing ‘lift’.  The wing should ‘lift’ up the string.  I may require some trial, to position the hair drier just right. Have a race with your friends.  Whose wing can reach the top first?

 

Can you explain what is happening to your wing? 

 

If you were able to get your wing to fly up the string, you created lift.  The aerofoil shape of the wing caused the air to move faster over the top of the wing than the bottom.  The lift was greater than the weight of the wing, so it moved upwards.

How does a plane wing work? Thanks to Dave Hax for the video

Glossary:

 

Sail, hēra.

 

Buoyancy, puhautanga - The ability of something to float in a liquid.

 

Displacement - The moving of something from its place.

 

Life jacket, kahu kautere.

 

Upwind - Sailing in the opposite direction in which the wind is blowing.

Downwind - Sailing in the direction in which the wind is blowing.

 

Force - A push or pull on an object.

Windward - The side of a boat that is facing the wind.

 

Leeward - The side of the boat that is sheltered from the wind.

 

Luff - The front or the leading edge of a sail.

 

Leech - The back edge of a sail.

Foot (of a sail) - The bottom edge of the sail.

 

Woolies - Or tell-tales are the strips of ribbon or wool on the side of a sail.

 

Waka - A traditional Māori canoe.

Kevlar - A very strong synthetic fibre used to make sails and bullet proof vests.

 

Carbon fibre - A very strong lightweight synthetic fibre used for high performance products like sails, boats and aeroplanes.

You might also like to try these other activities from HOW SAIL BOATS WORK

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SAIL POWER

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SAIL AWAY

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FLOAT YOUR BOAT

Do you want to learn more about the wind?

Try these learning experiences as well.

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A FORCE TO BE RECKONED WITH

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WHEN THE WIND BLOWS

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FEEL THE POWER

OF THE WIND

And when you think you have learnt enough then it is time to design your own technology to harness the power of the wind.