More boat testing.

My home made boat used a flapping foil (fishtail) for propulsion and although it did propel the boat forwards it had too many difficulties which I considered insurmountable. It didn’t move me nearly quickly enough and caused the boat to bob up and down. I decided to completely change the way in which the boat was propelled whilst still keeping it leg powered. I built a new system which powers the boat like the feet of a duck and thought it would have several advantages. Firstly it would be far easier to do calculations to help in the design. With the flapping foil it seemed as if trial and error was the only way to gain insight but now simple arithmetic would reveal a lot. My new paddles would actively claw the water like an oar and allow me to get far more energy in the water to do the job of moving me forwards. With the system built I took the boat for a test a couple of weeks ago.

Some bolts came loose and the boat just wouldn’t steer in a straight line. I didn’t post about the trial because the only thing I found was that I felt far more resistance when I pedalled, which did give me some hope. I’ve now welded the offending joints firmly in place so it was time to try again.

Nice lines with the boat on it’s wheels for transport.

I dragged the boat outside the garage and gave it a good look over. All seemed fine so I wheeled it down to the Leeds/Liverpool canal, donned my life jacket and launched into the water. As soon as I cast off I could tell that the rudder was having no effect. This I don’t understand since it seems large enough to do the job, though I was aware that it conflicted with the paddles at one point in their movement. I resolved to use my emergency paddle for steering and left the rudder alone. I found that when I pushed the pedals, or more accurately treadles, I could hear a noise as something was catching. I had to pull to the right to allow a large narrow boat to pass in the opposite direction, the pilot looking totally disinterested. I then went back to the left bank and climbed out to examine the problem. I found that a rotating cross member was hitting the plywood as it moved. I got back in to return to my starting point. I found that if I supported the rods which attach the treadles to the cross member I could reduce the problem but it was difficult to maintain a good, regular stroke. I knew that I still had work to do but I’m thinking that I can overcome the difficulties for my next test.

Using a bizarre invention gets you into a surprising number of conversations but I’ve found everyone to be unexpectedly interested and positive about my efforts. My issue today was again merely a loose nut which was quickly fixed back at home. I want to improve some parts of my propulsion system before another trial but must do something to make it steer properly. It’s the kind of challenge which I love and I have ideas already. I used the app. Strava to record my journey so how fast did I go? Strava gave my average moving speed to be 2.1 mph with a maximum of 5.1 mph. I’m not sure how true these figures are and certainly don’t believe the top speed. A boat of a little over 7 feet at the waterline can only reach a shade over 4 mph without planing, that is skimming across the surface, which is never going to happen in a human powered dinghy. For that reason my target speed is rather conservative and a cruising speed of a good walking pace is my main aim. It’s nice to be out on the water and being able to explore further is a great prospect.

Damaged woodwork where a component caught.
The rudder raised for transport. Why it doesn’t work remains a mystery.


  1. bgddyjim says:

    That’s an interesting fix… as I read the post, I tried to imagine how you accomplished what you were describing… the solution is pretty cool, I gotta say. 👍

    Liked by 1 person

    1. kirkmtb says:

      I get an 80cm sweep of the paddles so at a cycling cadence of 60-120 Hz that’s 160cm to 320cm per second. Multiplying by 2.2 for mph gives 3.52 to 7.04 mph, potentially. I wish! It’s already faster than you could row a small dinghy but I need to get it working well to get the best out of it.

      Liked by 2 people

      1. bgddyjim says:

        Super cool, man.

        Liked by 1 person

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