ekayak?

Didn't know where else to post this.
I just got an ebike for Christmas. The thing is a hoot. 750w hub motor, 48v 21 a-h battery...
Here's how this relates.
Seems a simple matter to take an ebike kit, apply a propeller, seal the whole thing and off you go! Batteries, twist and go controllers, and hub motors are all ubiquitous anymore and those for ebikes are sealed. Need a high speed prop designed to go 21000 rpm since that's what my hub motor spins at when I'm at 20 mph.
Anyone done this?

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

OOPS bad math.
21000 revolutions in 20 miles. Now have to change per hour into per minute so divide by 60...only 350 rpm...that's more like it.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

If you were to use a paddle tire you could also use it to cart your kayak across the beach.

If you go to an rc airplane shop you can pick up a 2 blade prop, I'm guessing off the top of my head an 11-6 prop should do the trick with that motor. If you run into hp issues just keep reducing the od, you will likely end up around 9".
One big issue you will have is keeping the motor cool in a sealed housing.
Attaching the armature to the prop will also be an issue (not really designed for the application).
It will likely take a pair of motors to propel a larger boat
Good luck
FE
Edit: you might be better off not trying direct drive (electric motors have very little hp, and the rpm's are typically to high for water. If you go to robotics web sites you will find in line gear reduction heads (from companies like Dewalt), similar to the front of an electric drill. The bearings on the motor amatures are not designed to take any lateral load, and there is no means within the motor to counter the linear load from the prop pushing forward,(thrust).
Good luck

Dang, good description.. But I need to be an engineer to understand what you are saying.... Could you speak a little louder?

I had in mind an outboard when started this thread. Now, I am thinking more along the lines of an ebike where the motor just helps you pedal or takes over when you are too tired to pedal. Imagine a mirage drive with a torque sensor (like on some ebikes) where the motor provides power based on your max push. I suspect Hobie could figure it out if they thought there was a market.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

I`ve never looked at e-bike kits before this thread, very interesting thank you. The e-bike motor has a full revolution with no reverse. Oops, I forgot about the 180.

Buy a $3000 e bike, rip it apart, throw away the bike, rebuild the motor as an outboard, solve the problems of waterproofing and corrosion, buy a propeller, work out how to attach it to your Hobie kayak (optional steps: test it, find it doesn't work as well as you thought, start again or throw away), enjoy

...OR...

Buy a Hobie Evolve drive, enjoy.

I know where I would invest my hard-earned cash

Actually I built a motor for my mirage drives a few years ago that used a battery powered power drill. Basically rotary motion converted to peddle motion by arms on a sprocket. It actually worked well but the powerdrill battery pcks went dead in about ten minutes. An ebike motor with a nice battery would probably work nice.
Good luck
FE

To get 2 hp, you need 1500 watts. a 48 volt battery driving a 1500 watt motor needs 30+ amps; to have it last 2 hours you need 60+ amp-hours. This is do'able but it will be expensive. My ebike has a 750 watt motor and a 21 amp-hour 48 volt battery. The system is only designed to let you go 20 miles (or one hour full discharge). 1500 watt ebike hub motors exist. 60 volt li-ion batteries also exist and that reduces the amps needed to 25...2 hour range then is 50 amp-hrs. It is do'able; I'm sure someone will do it eventually. Hooked to a hobie mirage with a torque sensor you can extend your pedal range quite a bit.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

That pedal thingy I made I drove with a Ryobi 1/2" powerdrill with I think an 1100ma battery (standards battery pack). I believe the drill delivers 25 ft lbs of torque (1/2hp) for about ten minutes. At I think around 600 rpm (in low). It pedaled my mirage drive quite well, I could also pedal with my feet at the same time, or disengage the belt and pedal without it.
Hope this helps with your power calculations.
FE