Pedal Powered Prop Design [?]

Hi guys, I have very little knowledge on prop design and I have a school project, which is to make a pedal powered water raft.

I plan to fabricate my own prop if I wont be able to find a commercially available one.

Can you guys give me an idea on what good prop to use?

- 400 kilograms of weight (consisting of 3 people + the bike + others)
- Doesn't need to move in a "fast" pace, just as long as it will move, its fine.
- Gear ratio from pedal to propeller shaft is about 7-8.

 

Look up Rick Willoughby's (he's off the board at the moment, but is probably the pro on these things) threads, Pedal Powered Boats for example. His posts are under the name Guest625101138.

His thread listing

I think he's written a tutorial on building a prop also, just don't remember where.

Here's how I made my composite propeller Building a small trolling boat #93

Hope this helps
Lurvio

 

I have heard that some folks use glass-filled polycarbonate model-airplane propellers in pedal boats I have experimented with these in trying to get more speed out of a trolling motor. More speed, yes, but not necessarily more efficient: The ampere draw (therefore: resistance to rotation) can be high. I think the big drawback is that near the hub, an airplane propeller can be quite chunky, but a boat propeller probably needs to be more svelte. But if you are experimenting, there are a lot of different diameters and pitches of strong model airplane propellers "on the shelf" and pretty cheap. Caveat: not at all "weed free"

 

Large, two bladed airplane props work great but each pedaler is only going to produce about 100 - 150 watts (0.15 - 0.20 Hp) so if only one pedals (one bike) with all that weight, you're going to be hard pressed to make any headway at all if there is any current or wind against you OR simply too much drag from poor hull design.

I do believe you're going to have to get everybody on board pedalling.

-Tom