[hpv-boats] Prop

[Kevin Batdorf]

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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