[hpv-boats] Fin-drive redux

[Larry H. Smith]

Hi Bob,

I'm confident that  Rick is right on top of propellor-stuff, but I'd 
like to hear more about your fin-drive ideas.

Max efficiency is less of an issue when "messing about " is the goal, 
and freedom from weed-wrapped props with the convenience of a kick-up 
drive, combined with the fish-like grace of a flexible fin appeals to 
me.

I wouldn't mind resorting to a paddle for the occasional reverse 
requirement.

I liked the relative simplicity of Harry Bryan's rig, as opposed to the 
bulkier drive that was later developed and discussed for awhile on this 
list. Seems I remember some sort of transparent flex fin on Harry's 
early experiment. I like the esthetics. ;-)

Harry ultimately used a forward fin(skeg) to counter yaw effects, ...I 
was wondering if you had any other ideas on yaw control.

I was wondering whether a split fin with stacked halves in opposed 
motion  would be feasible, or would turbulence between the flow between 
the fin-halves interfere too much to be useful? (Picture a swim-finned 
diver swimming on his side)

I would value any comments you might make (Others' opinions welcome 
too.)

Larry (Bob, I'm not sure if we have communicated via e-mail since your 
move(s?). [ My e-address is lhsmith at wvi.com ]

> I used to make pedal-propeller drive units.  They were quite 
> successful, but perfection as a product became quite expensive.  One 
> peculiarity of human power is the fluctuating torque, so that most of 
> the time, the propeller is operating far from its most efficient rate. 
>  The fin-based drive on the Hobie Mirage has to reverse direction at 
> the end of each stroke, but this probably involves less friction than 
> keeping a propeller moving at a constant speed.  If I were building 
> another boat now, I would use some kind of fin drive, and try to 
> design the basic unit so that it could be built and maintained 
> wherever wooden boats are made, without any purchased hardware.  I 
> have sketched out several possibilities of varying complexity, size, 
> and efficiency.  I expect that they would be as fast as propeller 
> drives, and better around shallows and weeds.
>
> Bob Stuart
>