Propeller tips...

Great propeller tips for designing or buying a propeller for a high performance pedal boat, from Rick Willoughby

The propeller is one of the key components of a waterbike: the performance is highly affected by a low performance or poorly chosen prop. Rick Willoughby, the designer and builder of some of the finest waterbikes in existence, gives us a few great tips for designing or sourcing a good propeller (from HPV-boats):

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: 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: 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: These props cost $14. The smaller ones for a single person boat are usually around $8. (RW)

We are looking for designers and suppliers of propellers. If you can lend us a hand in this search please contact us.