I finished some modifications to my newly built boat yesterday, with the intention of testing today. After my last test I thought that I needed to gear up the paddle wheel to make it rotate more quickly. After a little thought I realised that this would be the wrong approach. I simply hadn’t been getting the power into the water but had been creating lots of splashing. Gearing up would have made even more splashes but it’s doubtful that it would have got the boat going any quicker. I surmised that what I actually needed was a greater area of paddle in the water, gaining traction to drive the boat forwards.
Unfortunately, in a moment of disappointment at my lack of speed last time out, I’d neglected to take any measurements of how far the paddles on my wheel were dipping into the water. I therefore didn’t know exactly how much lower the paddlewheel needed to be so I set about trying to calculate. I divided the hull into 2 elements with known centres of bouyancy. Each would provide a vector pushing upwards, dependent on depth of submersion. These would be opposed by the centre of mass, which lay, I believed, 19 cm behind midships. With a bit of jiggery-pokery I estimated the angle that the hull would rest at, with me on board, and it was no wonder that I wasn’t getting much drive.
I tried 2 different methods which predicted that the paddlewheel was only dipping into the water by 4-6 cm, instead of the 12 cm which would represent a level hull. I needed to move the paddlewheel spindle downwards and, in order not to make another difficult to rectify error, I chose to make the position adjustable, needing only the drilling of 4 holes. I dropped the paddlewheel by 6 cm for my first try, which was today’s mission.
I took the boat down to the water in 2 parts, stacked on top of each other. A curious sight, I’m sure, but easy enough to accomplish. I then bolted the halves together on the canal bank and pushed the boat onto the water which is a drop of around 30 cm. I locked the rudder in position and climbed aboard. The stability, compared to the dinghy I had previously, is impressive. I set off, moving for a short distance, then thought that I should check my depth of paddle immersion. It was 10 cm, so in line with my calculations. Another 2 cm would, I think, be ideal and this will be easy to do. Previously I’d only been getting 4 cm of immersion. Good for cappuccino foam, not good for drive. I paddled around and found that a good cyclists cadence (speed of pedal rotation) of 90 rpm took some effort, promoting breathing, whilst not overly stressing the leg muscles. Speed felt similar to the dinghy but the leg muscles were finding it much easier in, or is that on, the new boat. Turning was an education.
I wanted to turn around and the boat seemed to turn well initially but was caught by the breeze of 21 kmh of 13 mph. This kind of windage rarely affected the dinghy but the slab sided hulls were really catching it. I had to use my emergency paddle to complete the turn on the 30 feet wide expanse. I pedalled back into the wind and tried various speeds of rotation. Later I heard and felt a clicking from the chain so docked to increase the chain tension. It was to no avail since I derailed the chain and had to paddle to the bank. I replaced the chain and chose to take it easy just to get some more time on the water. A lot of people were showing interest in the boat and speaking in very complimentary tones. A big group of cyclists stopped to ask various questions.
I did a final sprint finish and could tell that my speed increased to a good rate, considering my modest ambitions. I’d sailed for almost a mile in total and gained some valuable information. What I now intend to do is to drop the paddlewheel by a further 2 cm and make it impossible for the chain to derail. I was delighted that the boat was much less stressful on the legs than its predecessor. I think I will achieve my speed and distance ambitions and love the safe feel on the water. As I returned the boat to dry land a man was impressed that I was confident enough to be wearing ordinary cloths, rather than a wet suit. This reminded me that I’d forgotten to bring my flotation aid so it’s as well that I didn’t need it. I should be back on the canal in a few days.
Mountainbiker 