[hpv-boats] Prop

[Bob Stuart]

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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