If you have set up a water test tank in Boat shapes, you can use for testing sails as well. These boats are easy to make, but you will need a fairly large tank to test them in – they are really too big for a washing-up bowl.

These boats use two small water bottles to make a stable hull, and a bbq skewer to make a mast. Square-shaped bottles are easier to use than round ones, because there is a flat area to fix the mast on – but you can use round bottles if that is all that you can get (it is just a bit more difficult to fix the mast on). [Something to think about: You can buy still or sparkling water in round bottles, but you can only get still water in square bottles. Why? Perhaps Fizzy Drinks may offer a clue].

Before you fix the mast, wrap a little masking tape around the mast – two or three turns should be enough – this is just so that the sail will fix on the mast without spinning round. Once you have fixed the mast onto the side,put two bottles together, so that the mast in the middle of your boat.

Now try different sail shapes on your boat.

You can make some “wind” by flapping a piece of cardboard up and down. Which is the best shaped-sail for moving your boat along the tank with the wind coming from the side?

For careers involved with this sort of investigation see Transport and Aerospace

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