Efoil motor etc for boat

This seems to be a very knowledable community. I hope your knowledge can help my project(s) too.
I want to have electric motor on a boat
An electric outboard trolling motor would do the job just fine, but as you can see from the picture, there is no place to mount an outboard. So I’m considering to use some of the gear you guys use for efoils. The boat is 18-19 feet long, and only weighs 70 kg when dry. After soaking water for a few weeks + people and luggage, it could reach 250 kg. Hull speed is around 5 knots and is the top speed I’m aiming for. These boats usually get that with a 2 hp fossil fuel outboard (mounted on very annoying iron frame on side of boat). So I’m guessing 1500W motor would be fine?
I would have to mount it on the outside of the boat. Rudder would have to be modded in order to get room for prop + motor. But there are limits to how much I can mod it, so motor would have to be as short as possible. Alternative would be to mount it as an integrated part of the rudder (back of rudder -not below), but I’m not very exited by that idea. Feel free to convince me that’s the best solution.
5 knots is of course a lot slower than what you guys are going, so I don’t expect to use the same motor as you do. But I’m hoping for input on type of motor or specific motors that would do the job. Also input on everything that goes with them like ESC, cabling, remote controller, and propeller.

So, I have done a little research. As mentioned above a 2hp outboard gets this boat to my speed target of 5 knots. That’s with a 7.25 inch prop and 5 inch pitch at 2500 rpm. (Motor at 5000 rpm 1:2 gear ratio). I intend to use the same propeller as it has proven itself for this boat. So I need a motor that delivers the same torque to propeller at 2500 rpm. (Higher rpm will give little to no gain.)
Here’s where I’m a little confused atm: 2hp is close to 1500w. Does that mean I need a 1500w direct drive or a 3000w direct drive because of the 1:2 gearing?
I have a hard time finding waterproof bldc motors with only 2500 rpm that deliver enough power, Do you know of any good ones? Or do I need to buy higher rpm and use gear? If gear is needed, what kind of gear has worked for you guys back in the days when you used gears?

Btw. I have come to the conclusion that the motor and prop have to be integrated in the rudder. Not enough room for other option.

You could also use an outrunner run wet, you would need to coat it with epoxy and change the bearings against stainless. If run in salt water you might have to change them after some time and rince the motor with fresh water after use.
This one could work, 80kv and more torque than a 63mm inrunner: https://alienpowersystem.com/shop/brushless-motors/80mm/c80100-outrunner-brushless-motor-80kv-7000w/

Thanks, I was wondering if outrunner could be an option. Do you know of any build threads or videos that show successful waterproofing? Preferably one that has been copied successfully by members of this forum?

There are several including myself. Most that started with 80100 moved to 63100 as they are
more efficient for efoils. That was before the 65161 inrunners were available. That is the main reason you don’t find that many builds with outrunners.
A 80100 might still be ok for your purpose, as the effect of higher drag because of the bigger diameter, is worse, the faster you go.

Here how to treat a 80100: Volker’s Build - 80100 18650-30Q - #16 by V_S

I read the build thread. Good read. But not enough detail for a noob like me on the waterproofing. I found one good video on youtube about battle hardening a motor. Is that basically the same?

I don’t know, what I did was: dipped the stator in epoxy (metal and windings). Cover the bearing space and the hole for the rotor (play doh works).
For the rotor I 3d printed a cover for the slots at the bottom of the can. For the shaft I used a shrink tube to cover it. Also covered the outside with tape. Some people filled the gaps between the slots with 3d printed parts, I didnt.
Then I poured in some epoxy and turned it around to evenly spread it. To cure it balanced, put it in a drill press (open side downwards) with slow speed for the first 30 min. There can build up some “drops” at the top of the can from driping out the excess epoxy. Either sand them down or use a lathe.
Here a link to a picture with stator and rotor of a 63100: Daniels (un)geared inflatable (slowly built) - #55 by sat_be

Démonter le moteur d’un HB électrique et l’insérer dans le gouvernail le reste n’est que des fils à rallonger et fixer le boitier de commandes

For once Google translate actually gave a good translation :slight_smile: What is a HB?

outboard in English HB is hors-board in French

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