Pedal Powered Boats

Mike
I thought you must have had a lot of weed or had broken down.

There is a fellow here building a 6m long version of V14. It is designed for his weight and 10kph. He will use a direct drive. He is actually making his own box using gearing from a 10" grinder. The boat is made from ply.

 

Vic
I expect it will find its own market. It should work as well as the rigid version and is a bit lighter.

 

curious...

I'm not sure I follow all this. I read allot of this thread about the airplane propeller. I'm curious about another type of propulsion. Like a deep v surface driven. Where half the prop is in the water. I understand this reduces resistance and offers more speed.

I'd like to build a boat I can sleep on and be able to vary the speed of the shaft through 21 speed bike parts. I have an old Craftsman Angle grinder gear head.

Please explain in simple terms why a trolling motor prop surface driven may not work with pedal power. Also has anyone tried fiberglass tent poles for drive shaft? I was thinking of epoxying the sections together. I'm trying to be cheap not dumb

 

The back face of a surface prop does all the work. The front face does very little because it is ventilated - it cannot form a suction.

With a submerged prop the front face does most of the work - it is the suction face but pressure is limited to atmospheric pressure before it cavitates.

A surface prop will achieve a best efficiency of 70%. A submerged prop will achieve a best efficiency of 90%.

The difference in efficiency is not as significant once you allow for the drag of the supporting strut and submerged shaft. At higher speed with high revving engines it actually favours the surface prop because the reduced drag of the support and lower loss in gearing.

Pedal boats work at very low power level where large diameter props with high lift sections on narrow blades work well. Similar to what can be done with an air prop.

I doubt that you will get 70% efficiency with a pedal surface prop. Probably more like 40% by the time the gearing is set up. A submerged prop will be 80 to 85% for a heavy boat. There will be maybe 5W of losses in the supporting strut and shaft with the submerged prop.

One immediate problem with the surface prop is that the prop will move up and down in the water so the load will vary with waves. This is quite different to a prop behind a planing hull. There have been some large props used on model displacement hulls that got efficiencies around 60% but they were not tested in waves.

My surface prop got to 5kph at full tilt so maybe 10% efficiency but it was a better rain maker than prop.

 

awesome...

Thank you very much. That sums it up nicely.

 

Hope this helps.

Porta

 

You need the prop to be stiff in shear to transmit the torque and compliant in direct stress to avoid high stress when curved. The poles are not designed for this loading.

One thing I have been intent on trying is a aluminium rod wrapped in firbeglass/epoxy tape. The tape would be wound at 45 degrees. There would be a few layers of tape with successive layers wrapped in different directions.

A shaft like this should be stiff for torque and somewhat compliant in bending.

If you make one let me know how it goes. There are a few people looking at this idea because spring steel is hard to get and rusts unless coated.

Rick W

 

Rick, any idea about the % efficiency of single blade props (with the proper counterbalance) instead of surface piercing? Seems like the single would be more efficient than surface piercing because it remains submerged and the water in front would be less disturbed. I think they have been tried on airplanes and racing boats but the high rpms introduce vibration and bending stress issues to the shaft. Low rpms of human power should make that less of an issue. Maybe Java prop could be configured to give a quick answer....

Vic

 

Vic
I have seen people talk about this but it creates some nasty conditions for the shaft and supports. Hence these need to be heavier. It would not work very well without shaft support either. The counterweight would add drag as well.

You can devise a single blade that will be more efficient than two but by the time it is set up to work effectively I doubt that there will be any advantage over a 2-blade once the extra support drag is taken into account.

 

I thought you might find this interesting. Though the inventor claimed 20% economy of fuel for this prop plane, it obviously has never developed much

http://news.google.com/newspapers?n...eQxAAAAIBAJ&sjid=heIFAAAAIBAJ&pg=3138,4302554

Jeremy may get some amusement from this one also.

V.

V.

 

I think you'd be better off using a woven "sock", or "braided sleeve", which collapses down onto the core when pulled from the ends, like a Chinese finger puzzle. You can put on multiple sock layers, one at a time, and then saturate the whole thing with epoxy and wrap with shrink tape for compaction. Here's an example:
http://www.cstsales.com/carbon_braid.html
That outlet has good service but is somewhat expensive. I'm sure you can find cheaper outlets in OZ. Braided sleeve also comes in fiberglass.

 

direct drive unit

here's a pic of a direct drive unit

 

Mark
If I wanted to cover 1/4" diameter rod with three or four layers, what diameter sleeve should I get. Does it expand easier than it contracts?

 

It varies. It depends on how tighly woven the sleeve is. Typically the max/min diameter is 2.0 or more. I've seen some web catalogs which give the max and min diameters.
Or you might try getting a variety of sizes and testing. Cheap outlets sell the stuff for less than $1 / foot.

 

Mark
I will get some of the 1/4" and see how it goes. It is USD0.7/ft. I will do 4 layers over 1/4" spring steel if it fits.

I will measure the torsional stiffness before and after.