So, a couple of months ago, before I started my house, I had a couple of project ideas. One was an engine-powered kayak.

I decided to build my house, and gave up on the other ideas. But now, there's a couple of kayaks for sale for about 50 bucks, they were what I've been looking for, the occupant sits right in the middle, it has a rudder, steering, ect, and I've also found some very small, 50-ish horsepower engines for sale around on craigslist.

I'm done with my house for now, and I want to build this over the winter. I have a couple of questions about what do to about certain aspects of it.

One is about the propeller. How do I know how big the propeller should be? Also, all the engines have gearboxes. What do I do about that? Should I keep it and permanently put it at high gear? Low gear? Take it off completely?

In case it matters, I was going to mount the engine behind the occupant, and be a typical inboard-mounted, rudder maneuvered design. Nothing special, lots of things use this design, so I figured this was simple.

Anyone know what to do about the whole gearbox/propeller thing?

Thanks.

The propeller? I am not sure. Something moderately-sized ought to do the trick. maybe the propeller from the motor to a fishing boat. I see no reason to make it huge, and no reason to make it tiny.

As for the gearbox, you want to spin your driveshaft as fast as you can. I do not think a 50hp engine can spin a propeller fast enough to cause cavitation. Torque is not a big concern because there will hardly be anything holding the kayak back in the water--you won't be towing any waterskiers. And I've never heard of a boat with different gears. So either rip it off completely or just keep it in high gear.

I have started this project a long time ago & thats as far as I got.

I found a prop & the 90deg angle drive at a scrapmetal dealers, it used to have a 50cc 2 stroke moter on it but that was in peices.

Was gonna put another engine on it but I'm not confident with fuel engines & decided to use a small 12V moter from a car radiator.
I'll have a 12V car battery inside the canoe.

I intend to put the setup on the bow (frount tip) of the canoe so I can steer it.
It'll also be able to be taken off & put back on.

Thats about it.

So wait. Did you say you're looking to put a 50 hp engine in a kayak? What type of engines are you talking about, boat?

If you're just wanting something to cruise around with I'd use a battery powered trolling motor.

So wait. Did you say you're looking to put a 50 hp engine in a kayak? What type of engines are you talking about, boat?

If you're just wanting something to cruise around with I'd use a battery powered trolling motor.

To be specific, it's a motorcycle engine.

I'm not really looking for something to putter about in, I'm looking for a true speedboat, a true adrenaline rush, and full-size speedboats don't quite do it for me.

Oh yes, two other things: you'll want a kill-switch (a.k.a. dead-man's switch) so if you fall out, you don't get sliced to pieces (and so your kayak doesn't turn into an aquatic cruise missile). Also, wear a lifejacket.

To be specific, it's a motorcycle engine.

I'm not really looking for something to putter about in, I'm looking for a true speedboat, a true adrenaline rush, and full-size speedboats don't quite do it for me.

OMG! A motorbike engine!

Hell, connect it to a old turbo charger & make yourself a Jet powered Canoe.

Tie a rope to the stern & be the first to Water Ski behind a Canoe.

i've though about doing this myself, but come to the conclusion that its not worth all the trouble. even if it did work well its a bit stupid. but idk, thats just my opinion. i'd also advise you not to do this project though, because -no offense- you dont seem to have much experience with such things. but whatever, do what you want.


50 would tear the boat apart. a motorcycle engine is the wrong thing for this. the water would fuck it up, its too heavy, too powerful and would require a lot of modification.

the best thing to do would be to get a small outboard, modify it and rig that up somehow. maybe put a 10hp outboard through the hull or something. you would be better off with a sit on top kayak for this.
the people at kayakfishingstuff.com have made some trolling motor things. y

now, about making a "speedboat". kayak hulls dont plane, and if you forced one planing or semi-planing by overpowering it, it would be slow, unbalanced and very unstable at speed. kayaks also ride low in the water and are not great in waves, so adding the weight of an engine (plus framing, fuel, drive system etc.) would be a major problem even if you got the weight distribution perfect.

there are also numerous other big problems that im too lazy to type, but would become obvious if you think about this a little.

you are much better off modifying a different type of hull, like a small whaler or racing dingy if you want to make a diy mini-speedboat

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This, kayaks are very unstable, have you ever tried rocking in one? When you start paddling the whole thing really fast it sways a lot, so going fast with a motor any little body movement will fuck it up. And once you start tilting to the side theirs nothing you can do but flip.

Do some easy 1 and 2 rapids in an open top kayak and you will know what I am talking about.

Okay, so add some big fins to the bottom, saw off the back, and epoxy-glue on a flat plate. A truncated kayak hull isn't that different than the hull of a fishing boat or other boat that planes, aside from the tumblehome.

That sounds like a cool idea. Is the throttle going to be rigged to pedals? :confused:

Okay, so add some big fins to the bottom, saw off the back, and epoxy-glue on a flat plate. A truncated kayak hull isn't that different than the hull of a fishing boat or other boat that planes, aside from the tumblehome.

what would cutting off the stern and adding a plate do? if you know about some kind of epoxy that would hold that together, id sure as hell like to know what its called. also, a kayak hull is pretty different, and fins wouldn't really help the stability that much.

Damn, this idea went down the toilet about kayaks planing. I completely forgot about that.

Find a book about boat design, I know my grandfather always has a bunch. Some of the plans are pretty simple and it's something I'd love to try with more time/money.

I forget the specifics but one book had a simple wooden boat built for a motor. You could try modifying it and making it smaller to add to your thrill when on the water.

midnight (or anyone else who said theyve entertained the idea of doing this), did you get your insiration, or atleast visit, a site featuring this Shaun Baker guy?
http://tinyurl.com/2vwoe3
says his kayak has a 45hp jet engine. im assuming "jet engine" means like on a jet ski?

cost: $10,000

if ur doing a glorious recreation of this with salvage yard parts and craigslist purchases, wear a helmet lol

what would cutting off the stern and adding a plate do? if you know about some kind of epoxy that would hold that together, id sure as hell like to know what its called. also, a kayak hull is pretty different, and fins wouldn't really help the stability that much.

Regular-ass epoxy would do fine. If you were paranoid, you could use JB weld. In fact, one square inch of JB-weld has an adhesive strength of 1800 pounds per square inch. A steel disk the size of a half-dollar JB-welded to the roof of your car could lift it unsupported.

What sorta kayaks are they?

Regular-ass epoxy would do fine. If you were paranoid, you could use JB weld. In fact, one square inch of JB-weld has an adhesive strength of 1800 pounds per square inch. A steel disk the size of a half-dollar JB-welded to the roof of your car could lift it unsupported.tensile strength ≠ shear strength ≠ compressive strength

Yes, I'm aware of that. The tensile strength, which is the limit (along with the adhesive strength) is the property that you would be "testing" by lifting your car up. The tensile strength of JB weld is 3960psi.

Now, in the application we are discussing (epoxying a panel to the back of a kayak traveling through the water at high speeds) all of the properties you mentioned would be tested. Fortunately, JB weld has no real "weakness" in any of these; that is, all of the properties are on the same order of magnitude.

Anyways, I am completely convinced that standard epoxy glue would sufficiently hold a back-panel onto a kayak.

The keel design wouldn't take high speed from the rear of a kayak, it wouldn't get on the plane how ever placing the propulsion force more towards the center of the kayak beneath it could possibly work therefore its being pulled instead of pushed by the prop.
Turning would also prove a pain in the ass as kayaks weren't designed to turn like the a boat hull.
(Come summer, I'm outta here and on the salt water in my kayak) :)

What about the motor on the top of the kayak in the back and rotors attached to pontoons sort of like this but on a smaller scale.
http://imagecache2.allposters.com/images/pic/PTGPOD/638205~Pontoon-style-sailboat-Earth-Voyager-Pt-Huron-Posters.jpg

ah. Turning. Yeah, that'd be a problem, wouldn't it...


I think you're better off building/obtaining a hull that IS designed to plane. The more I think about the cannibalized kayak hull, the worse of an idea it seems like (although I do still think epoxy would hold just fine).

Well it would prevent roll overs. If he rolls over he might slip out head first into the rotors.

I forget the specifics but one book had a simple wooden boat built for a motor. You could try modifying it and making it smaller to add to your thrill when on the water.

This. We had an old one lying around when I was a kid that seemed to be little more than two slightly curved pieces of plywood. There was also one that looked the same in my highschool wood shop. ...I'm looking around for something similar, but it doesn't seem to be working.

Theres a whole class of racing jetboats that are made to have only one person in it.
They are a little bigger than a canoe & have (I think) the moter in front of the driver, & with the jet unit under the seat.

Theres a whole class of racing jetboats that are made to have only one person in it.
They are a little bigger than a canoe & have (I think) the moter in front of the driver, & with the jet unit under the seat.
Jet Sprints? yeah?
http://www.youtube.com/watch?v=xMhrxtjnX-A
If so 2 people and engine in the back.
Awesome to watch. :cool: