First, sorry for my english, I’m from France.
After reading almost all the threads of this very informative forum, I’ve decided to make my own build based on:
Target speed 20-30kph
I’ll keep you informed…
Good luck with the build. Always good to see a slightly different design. Where did you get the prop from?
The prop is an aluminium prop for Yamaha 2-3HP.
Bought on aliexpress for 9€.
c’est bien joli tout ça! (tu es dans quelle region ?)
numbers like good on the paper 
, i am building the same, i made a choice to put a bit more money on the built … will see
your motor is given for 10s, but carefour with 12s for the bearing and heat, don’t count too much on the 10c for the multistar, and for a constant application they are more like 2C
do you put a seal after the prop? , the bearing on the gearbox is not waterproof, when tested i got water in the motor… but i did not have a lot of grease inside the gearbox
Je suis à Lorient et toi ? Oui on est parti à peu près dans la même direction, n’hésite pas si tu souhaites discuter de certaines choses en privé (en français).
I know the AquaStar motor is given for 10S but someone on hobbyking said using it at 12S and 80A without heat problem. Peharps longevity will not be good at this voltage, but regarding the price (around 50€) I can cheaply replace it from time to time.
Regarding the batteries I think even 2C could be enough with a good gearbox and propeller. That correspond to almost 1500W. I plane to consume a bit less during cruising (around 1000W).
Yes, I use a double lip seal just before the prop.
Thanks for the comment!
I played with the same motor but in direct drive, using it at 6s pulling 2KW. I quickly burnt a current controller and a 120A ESC (aquastar) but the motor seems fine… i’m switching to a bigger motor though.
what i understood, it is more the rpm drop not the kw pull, if the motor is too small or not enough torque or the prop too big, the set up gives you kw but it is heat and the esc burns:
direct drive: 6s x 620kv = ±14000rpm but if the prop turn only around 7000rpm , 1000w waste power on the esc…
like on a real boat : good combo: engine kw/ prop size: better speed less fuel …
i am aiming for a 20% rpm drop on load ( the best way is to get a esc with datalogging to make a good setup)
I like this setup. I was going to use this gear with a bigger motor, but ended up with a slightly different gear.
Your gearbox: reisenauer motor Chef 6/1
“Max. Eingangsdrehzahl 50 000 U/min” … Interesting !
yes (the only one i found as well) , very good quality, need brake down a bit and cleaning and change grease 2-3 times, just the shaft needs m10x1, not easy to find, the thing about glue (or laser weld) the pignon too a 5mm motor shaft
Today I’ve performed first eletric tests.
I took the opportunity to measure some electric consumptions on a 10S battery, full throttle:
It’s interesting to see that the gearbox don’t “eat” too much power, around only 30W after severals seconds (when the grease inside become hot enough). Peharps more with some load?
The double-lip seal consumes about the same (30W).
Propeller in air only 18W.
I remenber to have read on this forum that an aproximately equivalent outrunner consumes about 80W with no load. That tends to show that an inrunner+gearbox have comparable efficiency that an outrunner alone (but inrunner is thinner and lighter).
Very promising data and setup you are building, it looks like Peters build or a lift model. You are using the same prop as i do for my direct outrunner, direct cooled. This thin pipe gives you a better oncoming flow for the prop than a cone could do.
I estimate the drag to be lowered by 10N compared to 63mm diameter at 8m/s.
Good luck!
Was the ESC getting quickly hot at full power ? The 120A esc limit looks at risk when the prop is in the water
Hi @philgib. The setup is using 126watts (power) in the air. At 10s say 42v this equals 3amps of current. 126/42 = 3. Cheers
Thanks. I hesitated a long time to follow you in the choice of direct drive outrunner for my setup. I like its simplicity. For rather slow speed, it might be a good alternative. A difference of 10N is not very important.
The sales rep from Neugart told me that they can add low viscosity oil (aimed for winter conditions) to allow higher RPM.
I would plan on cutting 25mm off the radius of the propeller to reduce the torque needed to turn it.
First test in water!
I get about 10Kg of thrust at 400W, after which a vortex is created and thrust is falling.
I need a bigger volume of water…
Looking really good 
. Do you have any information about the temperature specs. of the gearbox? Is there any cooling for the gearbox ?
as far as i tested this gearbox, i will be too not worried about temp
and yes the vortex created is pretty big with the solas prop, very nice set up to test, me i am in hurry to be in the water as soon as finish, so i guess i will skip this test part but you can get something like this: COMING SOON
many size , double wall, strong enough
