[hpv-boats] Prop

[Capn Jimbo]

I'm mostly a reader, but just had to respond to this one.  The fin vs prop 
comparison has been well done and the efficiency of the Hobie flippers is 
really pretty awful - nowhere even close to a human driven prop.

Unless you anticipate tripling the efficiency of the flippers you are 
destined to repeat the past...


----- Original Message ----- 
From: "Bob Stuart" <bobstuart at sasktel.net>
To: "Human Powered Vehicles -- Boats" <hpv-boats at bikelist.org>
Sent: Friday, February 25, 2011 3:08 PM
Subject: Re: [hpv-boats] Prop


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

On 25-Feb-11, at 1:48 PM, Kevin Batdorf wrote:

> Hi Rick,
> thanks for the info.It is very helpful. I really like the folding  prop 
> and the
> boat prop system. I have built a few recumbent bikes in the past  and 
> would like
> to build a recumbent for two on water. Something not to  complicated. We 
> live in
> the Dominican Republic at present and would use it on the ocean or  lakes 
> near
> by. Things are not so easy to find here but some things can be  built 
> fairly
> cheap. Where can I find information on the drive shaft and prop  system. 
> Much
> like what you have done.  I was looking at this hydrofoil bike but 
> thought I
> should start with something without hydrofoils and try to get the  prop 
> system
> first.
> http://www.human-powered-hydrofoils.com/hydrofoils/project-pedal- 
> aquaskipper/
>
> What kind of drive shaft and prop system was Alexander Gäbler using  at 
> this site
> http://www.human-powered-hydrofoils.com/hydrofoils/haiflyike/
>
> Thanks again for your help. Kevin
>
>
>
>
> ________________________________
> From: Rick Willoughby <rickwill at bigpond.net.au>
> To: hpv-boats at bikelist.org
> Sent: Thu, February 24, 2011 4:51:49 PM
> Subject: Re: [hpv-boats] Prop
>
> Kevin
> If you want a good result then the starting point is to determine  the 
> hull drag
> characteristics and the engine power curve.
>
> As an example I usually design for my sustainainable output of 120  to 
> 130W.  My
> slender stabilised monohulls have a total drag around 38N at a  speed of 
> 3m/s
> which gives me that power at the cranks.  The prop design process  is 
> iterative.
>
> The best freely available prop design software is JavaProp:
> http://www.mh-aerotools.de/airfoils/jp_applet.htm
> You need to set the values on the options page to suit water rather  than 
> air.
> You then select the airfoil section.  The E193 at Re# of 100,000 is  a 
> realistic
> starting point.  You can enter the design information you have on  the 
> design
> page and click the design command button to get a design.
>
> I use my own design software that has more flexibility than  JavaProp. 
> This
> allows me to produce somewhat simpler designs.
>
> All my latest props have been folding to make weed removal a matter  of 
> momentary
> coasting:
> http://www.rickwill.bigpondhosting.com/Folding_Prop.png
> There is little drag when they coast so you can stop pedalling and  keep 
> moving.
> They still have some limited reversing if you spin fast enough.
>
> This design avoids welding.  The hub can be toughened nylon or  other 
> plastic
> material rather than aluminium.  You do not need a lathe or mill to  make 
> the
> hub.  It can be done using a bench drill and decent file.  The prop 
> pictured
> took me 4 hours.  It has efficiency of 85% at its design condition,  which 
> it is
> capable of achieving most of the time because there is no lost time  in 
> removing
> any fouling.  When you have 130W to play with a single piece of  weed can 
> easily
> reduce performance.
>
> You can often find model aircraft propellers that will do the job  such as 
> an APC
> 16X16.  You will need to select gearing to suit it.
>
> I used a big model plane prop on this application:
> http://www.rickwill.bigpondhosting.com/Folded_Pedal_Thruster.JPG
> http://www.rickwill.bigpondhosting.com/Pedal_Power.wmv
> These props cost $14.  The smaller ones for a single person boat  are 
> usually
> around $8.
>
> Rick Willoughby
>
>
>
>
> Hi guys, thanks for the web page. I was wondering where I can get  info on 
> how to
> build a propeller for a man powered boat I am building. Thanks Kevin
>
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