Jet Kayak RC components

[mikebikerad]

Just finished this up. Cobra Tandem Kayak, Uses 2X Graupner Jet Unit 5. I still need to determine optimal RPM. Video shows jets running at ~8k rpm pulling 6kw, Will try the jets at 16k rpm this weekend

Update NOV 21st: Waiting on a new pump for water cooling, the original water cooling was not sufficient for the constant load.

Update August 2012: For an electric vehicle it is unbearably loud so now we are just using a trolling motor This project is now on the back burner, pending motivation and time.

[snellemin]

That's pretty cool.

[kfong]

Nice, how are they mounted?

[ohzee]

yea that looks awesome - great work. Love to see some more videos and how it's all setup.

[mikebikerad]

I'm thinking about tearing the jets out and going with an outboard setup, the boat is just to noisy, it like there is a jet engine on the thing. If anyone wants 2x graupner Jet unit 5's I'll give ya a killer deal.

[Hugues]

silence for a kayak is actually not bad,
i have one of these Hobie Kayak, the one with fins underneath that you power by pedaling,
http://www.hobiecat.com/kayaks/mirage/i12s/
i was thinking of adding some electric assist to it,
and maybe some hydro foil to get the thing out of the water,

which motor do you want to install and how is it going to be mounted ?

[mikebikerad]

I'm going to use a minnkota trolling motor but likely use this motor when it comes off back order.http://www.hobbyking.com/hobbyking/stor ... 780kv.html

[Hillhater]

Why use such a high KV rated motor ? .. you will need to gear down a lot and suffer low efficiency

[mikebikerad]

I wanted to use an inrunner so I could easily water cool them.

[Hillhater]

but if you use a suitable , low speed, efficient motor, it wont need any cooling. !
work backwards, figure your designed boat speed, the required prop thrust, the necessary prop pitch,diameter, rpm etc... then find a motor that best matches.
Unless you are trying to get up on a plane,..you should only need a few lbs thrust = a few hundred watts of power.
My understanding is the prop is the most tricky thing to get right.
Did you read through Jeremy Harris's threads ?

[mikebikerad]

Since I was using the jet drives I had to have high rpm(10-20k) at the prop to get any decent thrust from the small jets. For a two person sit on top kayak a trolling motor with a low kv out-runner and a nice big prop would do the trick. I picked up a cheap trolling motor and am going to do a similar conversion as some of the other boat threads are discussing.

In the jets defense they make a kayak sound like it is going 100mph but really only 4-5.

[mr.electric]

The noise level and pitch are both considerations. The Torquedo is not too loud but the pitch is a bit annoying. Low pitch noise is more tolerable.
The low end trolling motors are hard to beat. I looked at jet drives when setting up my canoe because it would allow operation in shallows but settled on a regular trolling motor. I have been happy with the trolling motor. The key is to use a nice lipo pack instead of Lead.

[dbaker]

Is that on the Sacramento River?

[mikebikerad]

Not the Sacramento. Much smaller river further north.

[mikebikerad]

Here are the jets mounted in the kayak. Bad fiberglass work but they were solid.

[mikebikerad]

I just took the jets out a few days ago and will be experimenting with a HK 50CC outrunner submerged as a trolling motor. More pics to come....

[Hillhater]

What prop size , pitch, & RPM do you plan on using ?
what will you use to waterproof the motor ?

[mikebikerad]

I'm using a 9'' minn Kota trolling motor prop dont know pitch yet (got on ebay)

I will run it on 4 cell lipoly and these motors are 172kv

I tested the motor underwater and it is totally smooth and responsive. I don't plan on using it in salt water. I will just run it for a little while after each use dry to spin most of the water out and then store it somewhere nice and dry, maybe get some ceramic bearing after a while.

[Hillhater]

..I tested the motor underwater and it is totally smooth and responsive. I don't plan on using it in salt water. I will just run it for a little while after each use dry to spin most of the water out and then store it somewhere nice and dry, maybe get some ceramic bearing after a while.

.. quite apart from the power lost to drag of spinning that motor in water ,..I suspect you are headed for a major fail very quickly !

[mikebikerad]

The load on the motor was minimal under water without the prop installed but you may be right, worth a try anyways for a simple setup. Worst case scenario it blows up or I might just fill in some of the cooling holes with epoxy to make it more streamlined. We will see by the end of the week

[mikebikerad]

Here is a quick picture with the prop, I should get a chance to test it this weekend on the boat. I might add a band in between the prop body and the motor case to combat the issue hillhater brought up.

[John in CR]

Fun stuff. You're a braver man than me just putting an outrunner directly in the water.

I'd think an inrunner would be better suited for turning into an outboard. Just totally seal the wires, add a waterproof coating, and add a 2 segment stuffing box on the output shaft. The problem is I couldn't find an inrunner with a low enough Kv, so maybe a planetary reduction is the answer as part of the stuffing box arrangement.

Put the outrunner inside a sealed tube with an ID slightly larger than the OD of the bell housing and fill it with the lightest oil possible.

[mikebikerad]

Hey John,

I was looking at doing a gear reduction but I couldn't find a good solution at least not an affordable one. Putting it in a sealed tube with oil is a really good idea, might try that next if I need to go into the ocean for some crabbing.

[grindz145]

Hah! That's Sick! You'd be way better off efficiency-wise with a trolling motor with a 2 blade prop. I just bought a 105lb trolling motor, 1.1kW for 200 bucks used on CL.

Theoretically it is enough to get my 2500lb sailboat up to hull speed (5.4mph).

But admittedly, that wouldn't be half as cool.

[Hillhater]

..I was looking at doing a gear reduction but I couldn't find a good solution at least not an affordable one..

Did you see this one..
viewtopic.php?f=39&t=33547