[hpv-boats] Prop

[Rick Willoughby]

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