In 2007 I constructed my BOAT, a plastic barrel, streamlined with a tub and a road cone and propelled by a lever operated monofin. Although this did result in forward motion the energy input did not produce a corresponding speed.
The sluggishness was caused by an energy leak: the pushing down of the monofin was causing to lift the hull instead of propulsing to its full potential. For my solution to compensate lifting with alternating fins a long lever is required. This would also take a very long floating body.
To increase the propulsing power with levers the body weight of the operater can be deployed. This would need a construction mounted on the floating body. To distribute the propulsive power for both fins I depart from a T-balance.
The tilting of the T-balance is powered by a rod suspended fixed swing upon which the driver is seated. The momentum produced by the swinging weight pushes and heaves the fins. The gravity that pulls the driver can be enhanced by rubber springs, like bike tubes, running from the extremes of the T balance to those of floating body.
This would constitute the human powered engine. Now I’d like to focus on the propulsive motion of the fins. Previous experience has taught me that increasing the propulsive shape of the fins should be sought in width as increasing length produces relatively more drag. This changes the perspective from a fin to a wing. The tilting of the wing can be achieved by hinging the leading edge to the vertical driving axis.
Once this construction is brought in motion, the down stroke at the front will exert, apart from the desired propulsion, an upward force on the float.
Simultaneously the up stroke at the rear will exert, also apart from the desired propulsion, a downward force on the float.
This prancing will be increased by my body swinging backwards.
Likewise my forward swinging motion will be pulling the front of the float down and lift the rear.
This would argue against this construction on the same grounds that proved the propulsion of my first boat less effective. The counter arguments are three-fold.
1- The down stroke works against the weight of either the front half or the rear half of the boat. The upstroke works against the front- or rear half buoyancy of the boat, which would probably be less disruptive.
2- The effect of inertia. There will be a delay between the action and the result. The faster the action, the greater the delay. As I see no way to predict this by calculation this is subject to experimentation.
3- The stabilising effect of water flow on fins. The fins cut a trajectory through the water, making them less prone to deviating from their course
A factor in the transmission of swing power is the leverage exerted by my weight. This force is passed via from the middle top of the T. The longer the arm from top to fin, the less leverage. So the shorter this arm, the more efficient the distribution of power. This would argue for straight, slant running arms from the top to the hinges of the wing axes, but these would obstruct the swing of my body. The best compromis would be a quarter circle arm.
Reversely, a longer arm between seat and top would render more leverage, hence a half circle connection.
Like wise, instead of two straight posts, two half circle ones would provide more stability.
This kinetic construction is subject to variations and its interactions cannot directly be foreseen. Experiments will have to render the most favourable configuration. Patent pending.
I realise the above is not easy to digest. So why not throw in some pleasurable videos, part one and two of the four part documentary ‘Dances with Dolphins’, which we shot of Dusty at Inisheer in 2014. Enjoy, and Best Wishes for 2017!