View Full Version : Need Pusher Prop advice for crazy project

12-12-2006, 03:11 AM
Hello all,
I am in the process of building a motor for my kayak (dont ask why lol) and am wondering if you guys could help me out with prop sizes, shapes, brands etc...I cant find any good websites that have a large variety of pusher props, and would like to stay away from wood props if possible as this will be a marine aplication.

First off I have a 14x7 three blade push prop which was the biggest push prop my LHS had. It pushes me better than I thought it would but I want the boat to go faster and hence need a bigger prop. I am using a weedwacker motor so I am assuming it will handle a pretty large prop. I was thinking somthing around 20x10?!?! Any and all advice is greatly appreciated, I know absolutely nothing about propellers. Thanks in advance everyone!!
John K

12-12-2006, 08:28 AM
More pitch will give you more speed.

Moving to "Off Topic Chit Chat", as this isn't related to anything about RC Flying which is what this web site is about.

12-12-2006, 08:41 AM
Why not just put a trolling motor on it? I have a 36 thrust on my Pontoon Boat and it scoots! Your Kayak will cut thru the water even better.
Click on photo to enlarge.

12-12-2006, 02:58 PM
you should look on a hover craft site.

12-12-2006, 07:02 PM
thanks for the responces guys, I could just go out and get a trolling motor but I enjoy building things and I had a spare weedwacker motor. So if anybody could just tell me a good website to get a pusher prop that would be great.

Now for somthing a little more related to this site. What do you guys think would be the minimum amount of money it would take to build an airplane?

WRX Dave
12-13-2006, 12:12 AM
Umm, build an airplane? A little more specific please...

12-13-2006, 03:25 AM
I spent some time working on slowspeed water props, looking for max efficiency. I eventually ended up with a cast bronze 15" 2-blader which started as an 11-6 Aussie prop. I was looking for efficiency, not speed, but they were capable of good speed on a kayak, at (comparatively) very little draw on an electric motor. One must also remember that displacement hulls are speed limited by hull length, so don't expect planing speeds on the weedwhacker motor, regardless of what you do.

The cast bronze was 20% more efficient than the original plastic prop, but you can cheat and use pewter; it is almost as stable, but can be cast in your kitchen (melting point is ~550deg, melts on a stovetop burner). Using your current 3-blader, you can modify it to get what you want from it. I suggest doing some math re pitch and hull length to get it right, but pewter is cheap enough to play with.

The game here is to experiment!

12-13-2006, 07:40 PM
Thanks TLyttle!!

12-15-2006, 04:15 AM
Hey, no prob! BTW, here's another hint about pewter: because the melting point is so low, you can use body filler for a mold. Wax the daylights out of the prop (acts as mold release). Build a box a bit bigger than the object (prop), mix a slow batch of filler, enough to half-fill the box, and press the prop half-way into the filler. Let it set.

Remove the prop, wax the prop again and the top of the set filler, mix another batch and pour it on on top. After it sets, remove them from the box (I just take the box apart), and you should be able to separate the two halves, and the prop should just fall out (If ya did it right).

Carve a pouring spout into the molds (remember that you are pouring into this thing) and whatever vents you would think are necessary. With a 2-blade prop, it is easy, just pour in one end, little venting necessary. With the 3-blade, ya gotta think it out a bit. Let it cool, usually an hour or so before you can handle it.

Anyhow, if the first one doesn't make it, it will show you the error of your ways, and you just change the mold to correct, remelt the pewter, and try again. Mold corrections can be made with auto surfacing putty.

This sounds far more complicated than it is, really. I have poured some interesting stuff using this method, including a hood ornament off a Singer Bantam sedan. When my bleedin' camera is working properly, I will post a pic, if you like...

12-17-2006, 05:17 PM
Rugar, I am sooooooo jealous......nice ponty!