[hpv-boats] Fin-drive redux

[Bruno Sertier]

Hello people!

Very interesting discussion here!
I'm brand new on this blog but I'm currently working on a pedal + propeller 
moved small wet submarine and have a couple of remarks/suggestions on this 
topic :
Good remark about variable torque (and RPM) when pedaling for actuating the 
propeller. Some inventors designed solutions to improve this : an "ovale" 
leading gear to compensate legs dead stroke and make the motion more regular 
and with a better efficiency already proven on traditional racing bikes (+10 
to +20% depending on promoted solutions : See http://osymetric.com)
An other way to damp this RPM variation is to adapt a rotation speed 
regulator and increase the angular inertia (it's mechanically very simple 
and cheap to implement). Only drawback : It's increasing a bit the overall 
weight and required some extra torque and time to speed up when starting 
motion.

Other question : I'm looking for a CFD software (such as Fluent+Gambit from 
Ansys or Flow-3D) else than the opensource ones, free but not always easy to 
use. Has anyone a clue about how to get an efficient and pro class one 
without spending a fortune (or downloading cracked, uncomplete, and of high 
risk of malware infection)?

Thanks

Bruno Sertier
http://www.scubster.org



--------------------------------------------------
From: "Larry H. Smith" <lhsmith at wvi.com>
Sent: Saturday, February 26, 2011 6:26 PM
To: "Human Powered Vehicles -- Boats" <hpv-boats at bikelist.org>
Subject: [hpv-boats] Fin-drive redux

> 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
>>
>
>
> --
> This message comes to you via the hpv-boats at bikelist.org mailing list, 
> sponsored by http://www,HuPI.org/
> Visit http://bikelist.org/mailman/listinfo/hpv-boats to manage your 
> subscription.