Anyway to make a homemade boat prop

Hey me and a friend are trying to make a cheap boat motor as a fun project. Anyway to make a prop? Or anything cheap we can use as one?

 

What sort of boat?

It is easy enough to make a sturdy propeller if you can weld with some proficiency and have some flat bar and a few other bits.

If the application requires relatively low thrust, meaning an easily driven hull, then you can get a very well priced model plane prop from here:
http://www.hobbycity.com/hobbycity/...ts.asp?idCategory=113&curPage=11&v=&sortlist=
These are more efficient than a typical boat prop but are not able to take the high force of a more normal marine prop.

You can usually get a cheap prop from ebay if you only want to play around:
http://shop.ebay.com.au/?_from=R40&_trksid=m38.l1313&_nkw=boat propeller&_sacat=See-All-Categories

The most important requirement for any propeller is to match it to the application. So you should have a good idea of the hull drag and intended power to start the build or buy process.

Rick W

 

make a disk helical drive achamedies style ,they are easy to make and work .i have made them out of plywood and they hold up ,try a garden mower engine and use ve belt drive out of a washing machine,went great in a daft raft race ,left the rest for dead. A steel 4 bladed fabricated is as easy using again a disk cut in 4 and welded at an angle on the boss,with the hole made first ,then set it up in plummer blocks and spin it against a scribe to true it using a hand grinder ,then drill into the heavy sides to get it to balance, i used it untill i found a replacement ,at the right price,

 

Aluminum or tin would be even easier than steel. You could cut out a disk with tin snips, drill your hole in the center, then 4 cuts in the disk in the shape of an X, but they don't intersect. After the four cuts, you have four flat blades, which you can carefully bend to get your desired pitch. You might even be able to do it with cardboard if you can fix the pitch with an epoxy coating or even fiberglass.

Only real disadvantage is you end up with more of a cleaver-style prop and you don't get any benefit of differential pressures on the blades to assist in propulsion. If you could mold the metal prop/blades in the same fashion as an existing prop (maybe use plaster-of-paris mold or similar with an existing prop), you would get some of the curve and cup of the blades that would give you differential pressures.

 

I've made a model boat prop in the way Village_Idiot suggests above - and soldered a nut to the middle. That way, you can screw it onto a threaded shaft.

It will be far more efficient if you twist each blade so that the angle of attack at the outer edge is less than at the inner part - sine of the angle should be proportional to the radius, so that it moves water the same distance at all points on the blade. Do that first, then add a bit of camber to make it more efficient still.

 

You could also make the plaster cast of an existing prop, then pour epoxy or acrylic resin in it to cast a finished prop....without having to handle molten steel. Or, if you REALLY like a challenge, you could cast the prop out of plaster of paris; bake it at about 200F for a few hours; then fiberglass & epoxy it to keep it from shattering...I still wouldn't expect it to last too terribly long though, first rock hit would prob. ruin it.

 

OK. So now we have plenty of ways to make a screw that pushes water. Who knows how to estimate pitch & diameter? that depends on how fast you expect to go (fine pitch and big blade area for tugs, coarse pitch and smaller blade area for the big Merc on the back of a racing powerboat). See if you can find a commercial product doing roughly what you expect yours to do, and use that as a guide.

 

Hmm, for a

I'd recommend looking a some trolling motors to get an idea...maybe you can even find one in a junkyard that you could salvage the prop from? Then you could use that prop, or use it as a "plug" to mold your own from...it all really boils down to "how involved" to you want this project to be? You have to decide if your goal is to get a cheap motor for your boat, or to build a motor for the sake of learning & taking pride that "We MADE this motor."