BuiltWithNOF
Boats

Boats are fun to make and there are all sorts of ways to power them. It takes a long time to make a wooden model boat so I like to use plastic milk bottles.

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This wood strip boat is being built by year 6 from Percy Main Primary School in Wallsend very near to a famous shipyard (now closed) on the River Tyne.

Each wood strip is only 1cm wide and quite easily bends to take the shape made by the inner formers or ‘bulkheads’.

When the woodstrip layers are finished it will have to be sealed inside and out and waterproofed with layers of paint. Then lots of ‘ballast’ in the form of small stones will have to be placed low down in the bottom of the hull around the ‘keel’ as ballast so that it balances properly in the water. (see the ‘Cutty Sark’ page to see this in detail).

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Plastic milk bottles cut in half along their length are fantastic for making boats. I have made a wooden dowel mast fixed to the bottom of the boat using a piece of blu-tac. (A better way to attach the mast using a block of plastic foam is described below). A card sail has been added as well as a pirate.

It floats really well but can easily topple over so it needs some small stones or pieces of plasticine as ballast to make it more stable in the water.

With a larger bottle you can try more adventurous designs and more masts and sails. You can even model a real sailing ship by copying the position and number of masts and shapes of sails.

Why do the designs of real sailing ships and yachts vary so much?

This one has two hulls! It is made from 3 milk bottles held together by long wooden dowels. Two of the bottles act as hulls and are in contact with the water. The other is the main body of the boat which is above the water.

This type of yacht is called a ‘catamaran’ and it is a very ‘stable’ design which resists being blown over by the force of the wind even though it can carry lots of sail. The forces are shared out across two hulls spaced apart rather than one hull in the middle as with a normal ‘mono-hull’ vessel.

Foam blocks are ideal for attaching a mast and sails to any shape of plastic milk bottle hull. They don’t have to be glued and weigh very little. The hole for the mast is made with a pencil or pointed wooden dowel as a drill. The mast can be a plastic straw or a wooden dowel. The sails are made from card and they can be waterproofed by laminating them.

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This picture shows a 4pint plastic milk bottle which has been cut in half along its length. A rectangular foam block has been cut just the right size to fit inside the hull and it is held in place by a single elastic band which stretches around the bottle and over the top of the foam block.

Flat bottomed boats are not as fast or as stable when carrying a cargo as those with a ‘V’ shape hull.
You can easily make a ‘v’ shaped hull by cutting a 2pint bottle along the edge rather than along the side as shown below. The picture isn’t very clear but you can make out the top of the foam block which sticks out like the sloping roof of a house.

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A ‘v’ shaped boat must be properly balanced by adding weights called ‘ballast’ in the lowest point of the hull. Because of the ‘v’ shape the ballast (small stones in this case) falls into the very bottom of the ‘v’ easily and so it is fairly easy to balance the boat so that it sits evenly in the water and resists being toppled over by the force of the wind on the sails.

Different sized bottles may require different sized foam blocks and varying amounts of ballast to make them stable in the water.

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Look closely at the boat which is 5th from the right in this picture. It is ‘V’ shaped rather than flat bottomed. the drawings below show a typical 2pint plastic milk bottle. The various views show how it can be cut to make two  ‘V’ shaped hulls.

BOAT milk bottle FINAL DRG

A
View from above looking down onto the bottle. This is often called a PLAN view. The large black circle is the mouth of the bottle and the smaller dashed line circle to the bottom right is the position of the plastic cut out which forms the handle of the bottle. The red line is the CUT line. Uses a pair of scissors to slowly cut a little at a time around the bottle starting at the mouth and following the direction of the red line down the side of the bottle, around the bottom and back up the other side.

B
This is a side view of the bottle showing clearly the handle slot.

C and D
These diagrams show the view from the front of the boat hulls as they would appear in the water. C has the handle slot but this is not a problem and it still makes a perfectly good boat hull.

E
This is a side view of hull D (why is it not hull C?). Small stones have been placed in the hull and because of the ‘v’ shape they will fall down to the bottom of the ‘v’ and make the boat more stable in the water.

F
This view shows a plastic foam block in the hull. A hole has been made in the block using a pencil or pointed wooden dowel as a drill. A straw or wooden dowel can be fitted as a mast and a card sail can be added. An elastic band is used to wrap around the hull over the top of the foam block to keep it in place. Hot glue can be used instead if available - only a small amount is needed because too much will melt the foam and plastic hull!
 

Here is how to build a motorized milk bottle boat.

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The ‘air propeller’ which fits on the motor axle is made from a piece of plastic milk bottle by drawing a circle on the plastic then cutting out neatly with scissors. Then mark evenly the positions of lines radiating from the centre. This propeller has 8 segments. Cut most of the way to the centre along each line then twist each ‘blade’ the same way to obtain the ‘fan’ shape. Pierce a tiny hole in the centre of the propeller so that it is a tight fit on the motor axle.

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Two more elastic bands are used to hold the foam block in position in the hull of the boat. The foam block in the hull is a snug fit so it doesn’t slide about - this is important when the motor is turned on and starts to push the boat along!

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Some modeling foam blocks have been prepared. One has a hole for a battery and the other which is longer but thinner has a hole for the motor. The two blocks are joined together using a partly sharpened wooden dowel which pierces both. It’s best to make the pierced holes separately first then bring the two pieces together with the dowel between them.

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The wires from the motor have paper fasteners fitted to the ends to make a better contact with the battery. They are held in place by an elastic band. One of the paper fasteners can be modified to make a switch to make it easier to turn the motor on/off (see the Torches page for switch designs).

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You can experiment with different designs of propeller for your ‘air power boat’. Which design will work best - one with lots of blades or a bigger propeller with only two blades?

There are two important things still to consider! First - the balance of the boat because the motor is quite heavy but rather high up, and second - how can the boat be kept going in a straight line or be made to change direction?

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