Cardboat 2012

The boat was transported to the race "flat-packed" in the back of a mini.

Powered by a paddlewheel and steered by an oar, both made from cardboard.
Surprisingly successful.

In sharp contrast to the boat, there are a  lot of edges in the wheel construction exposed to the water. If they are not very carefully taped up the whole thing will become waterlogged and turn to mush in seconds.

The boat took about half an hour to tape up on-site. The wheel took about an hour to construct and tape together on site.

 It felt like there was just the right amount of resistance turning the paddle wheel and that it was really propelling the boat forward at a fair pace. The crank handle turned smoothly. No doubt it helps that the boat itself cuts through the water without too much resistance. The only improvement that might be made is some sort of construction to keep the axle level. This is tricky though because the space inside the boat under the axle is taken up by the paddle twizzler's legs. Perhaps the twizzler just needs to workout more.

On leaving the ducks (Mo and Jess) the novice wheelsman turned the wheel in the wrong direction and we went nowhere fast.

 

At this point the cardboard oar snapped leaving the oarsman with only a tube to paddle with.

 

 Luckily the oarsman had already pointed the boat in the right direction and the paddlewheel kept going at a fair speed to the finishing line.

With a little practice it might be possible to actually steer the boat with the paddlewheel. On the way out the boat veered to the left. On the way back it veered to the right. Evidently there is something either in the angle of the wheel or the tilt of the boat that controls the direction of travel

Video courtesy of Martha.

How to build a cardboard paddlewheel

Here's an idea for a paddlewheel.

 

Paddle design is only as good as the weakest point from the input force supplied by the occupant to the output resistance of the water. The smaller the paddle area the smaller the resistance and so the less force required but the less propulsion per revolution. The number of paddles also needs consideration.

Weak points:

1. Input force - Handle for turning the axel: Handle breaks rather than turn the axle
2. Output resistance - axel spins and spokes snap.
3. The axle could crumple, snap or tear under torsion. 
4. The paddles themselves collapse

As well as the paddle wheel failing, it also has the potential to destabilise the boat. Corrugated cardboard has a natural boyancy. If the paddle wheel sits too low in the water with the axel below the waterline it will not function well. If it sits too high then the paddle blades will just skim the surface.
The above design sits in the water just up to the top of the paddle and the radius of the paddle wheel is designed so that the axel just rests on the side of the boat. 
The paddlewheel is not fixed to the boat for several reasons. Firstly, it means that as the wheel  gets wetter and heavier it doesn't drag the boat over. Second, since the occupant will be sitting and not kneeling there needs to be space under the axel for the occupant's legs. Third, It allows the direction of the wheel to be manipulated to help steer the boat  a little.
Power is designed to transfer to the boat via the oarlock (this too needs to be strong enough not to snap, crumple or tear the boat). In practice, a lot of the power was transferred to the boat through the straight arm of the person holding the tube surrounding the axle.

Six blades seemed to be about the right compromise for a smooth rotation without having too many cuts in the disks. The disks were made hexagonal rather than circular so that taping and designing the paddles to match was easier. Each blade area is 20x20cm. Again this seemed a reasonable size. In practice the resistance seemed about right. Not too had to turn but provided good propulsion.

The axle was built from 3mm thick tubing of between 5 and 6.5cm diam. It was thickened by slitting extra 5cm tubing and wrapping three pieces around the 5cm diam axel until the 7cm tube fitted snugly over the top. These thickend tubes were drilled with a 30mm core cutter to allow 30mm diam. tube to be inserted. The 30mm tube is crucial to the design. Two pieces lock the wheel to the axle and two pieces connect the crank handle to the axle.

Care should be taken to tape all edges. If water gets inside the corrugations the glue will soften and the cardboard will soon lose its stiffness and collapse.

How to build the cardboat.

For anyone wanting to build the cardboard boat, here is the design used in 2010 and again this year.
The boat was designed to take two people, to be reasonably stable and manoeverable for a circular course,  and to float without any waterproofing.
It is based on the largest sheet of doublewall corrugated cardboard that I could buy from a box manufacturer. I had to fold it roughly 3 times in order to fit it into my car ( a mini). Extra folds are not ideal but you can get away with it.
You can modify the dimensions. Making the boat narrower than 62 cm will make it less stable but if you want to race in a straight line it might be worth the risk.  If there is only to be one occupant then it could be shallower on the sides as well as narrower. Be aware though that, by changing the dimensions, it is very easy to end up with bow and stern that point downwards so the boat won't sit flat on dry land. This may not be a problem if the boat is boarded when it is sitting on the water.

Plan view looking down on the inside of the hull.

Use a metal ruler or similar straight edge tool to press down on the fold lines while bending the cardboard, taking care not to puncture the cardboard in the process.

The cockpit could be improved but is adequate to fit inside the hull as specified above. Its purpose is to keep the shape of the boat.In particular, taping the cockpit to the bow and stern stops them being pushed inwards and upwards by the pressure of the water; taping along the sides of the boat prevents the boat from lozenging and the sides from being pushed inwards too much.

     

Plan view of the inside of the cockpit.

Cardboat 2010

The cardboard kayak handles well with good tracking i.e. when you paddle on one side the boat still goes straight.

The internal cockpit is taped to the hull and gives the boat rigidity and stops it from lozenging. The tape on the bow and stern pulls the two sides of the boat together while it is out of the water. Fortunately, when the boat is in the water, the water pressure on either side provides the force needed to keep it together.

 

Showing off the underside of the boat after a 20 minute paddle. You can just make out the waterline halfway up the side of the hull. Because there are no tears or exposed edges the hull remains remarkably watertight even without any waterproofing. One little tear, however and the boat would dissolve  very quickly.

Here's two videos of the practice paddle on the loch.

 

Finally. The day of the race.

On the trailer about to be lowered into the canal basin.

 

Pushing off . Easy does it.

Cardboat 2009

The first year of boat building was not too successful. 2009 boat had a rounded hull which looked very boat like but the centre of gravity was too high and the round hull made it easy to roll. The narrow cockpit made it impossible to lean very far to one side to balance. The boat was consequently VERY unstable. Making the boat longer would make it more stable but this wasn't possible with one sheet of the available cardboard.

Yes yes, Hilarious isn't it. That canal is filthy you know. 

Elegant-yes. Boatlike - yes. Well designed......er...

Lesson learnt (the hard way) and next year a wider, flatter bottom boat was designed so we'd have a chance of staying the right way up.