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I don’t think the sealings will be to hard. You have one before the Red Prop and one inside the Red Prop (where the hollow shaft becomes the propeller should be enough space for a bearing and 2 lip seals).
But how do you get a defined position of the green gear?
I don’t think there will be gearboxes in the right size.
I guess it would be easier with 2 motors, you also spread load and wear (e.g. on the ESC and cable/connectors).
One motor with over dimensional hollow shaft and a normal one going through. Since you are spreading load, maybe even 2x 50xx outrunners will work.
Maybe you can even design some of those:
to work as sealed Hub-Motors inside the props, the diameter inside the windings should be big enough for a strong rod to mount both on.
Just a quick concept. No seals etc , just looking at the available space! not going to do any more on this.
I think two independent motors would be better.
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This is what I want !!!
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@theone: vey nice 3D skills. I think it would be nice to create a new thread. As you’re the one who spot the topic … honour is yours 
Just wondering why torpedos and sub-marines gave up contra-rotating props in the 1930’s after WW1 anyway. Lack of efficiency and/or silence, too strong acoustic signature ?
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All,
The topic of counter rotating prop has moved to Contra Rotating Propeller - Propulsion System (Motor, Gears) - FOIL.zone
Lots of other clever design features @Gobbla has done with this design, electrical seals & not drilling mast well done Gobbla ! I will copy lots of your design .
Thanks for the inspiration.
Cheers,
Al
Trop forts les Lyonnais
On essaie d’être les premiers sur Villeurbanne alors 
Beau travail en tout cas !
@theone , dont hesitate, copy my design, improve it, share your result it will be my pleasure.
@Arue, i hope you will join us soon. 3 foil on same time on saone should be great ! 
sunday morning session :
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Gobbia Thanks for sharing. What gear drive are you using?
Neugart reducer +56104 motor
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Hello everyone, just few additional feed back on my last foil evolution.
I have replaced my neilpryde foil by gong foil one.
I advice every beginner to do not go on Neil pryde foil. It is really unstable, Difficult to learn. With gong foil you can start so quickly to fly on long distance. Flying speed is lower on gong foil.
Price is really more interesting on gong foil, installation is more easy…
Electric consumption is lower on gong foil, I just need to recalibrate my indicator and I will give you exact result
2x16ah - 6s: 20min of continuous flying
2x20ah - 6s : 30 min of continuous flying
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This is electric consumption of my foil during stabilized flight :
with motor touching fuselage of foil :
25A - 14Km/h
with motor 80mm above fuselage of foil :
22A - 14Km/h
Neil pryde :
36A - 19km/h
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Vert interesting stats!
Check out Himax CR6320-240
Diameter 63mm
85A x 2
3600W
240KV
$499.99
But strangely enough, only 430oz of thrust
hello every one, after 3 month of no use … just plug it again and its work perfectly.
for information i met cops on boat.
They were really interested by this concept. they take a lot of pictures.
they said : " we dont dont what is law for this kind of board so we will not ask you anything "
hope it will stay like that a long time.
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In many European countries, you don’t need a licence below 6HP or 4500W.
Did they ask you your electrical power ? Did you give them your address 
?
In Croatia, u can use 1.5HP and under 299 cm length. Anything over = licence and registration. However, we are so screwed we got different laws depending on the region of the country. 
Gobbla, we are building a similar very short / very thick board.
How wide is yours, and how do you start when the engine is still off ? Are you able to climb on it from being fully in the water ? Or do you start from a platform or pulled by a motor boat ?
Thank you
philgib, my board is 1800 x 610 x 140 mm
almost 110L
i start on my knees, i can sit on it :
it’ s really convenient when water is cold or if you want to take rest out of water.
only problem is when there is waves , it take more time to get enough speed.
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soefoil , they did not ask me any thing on power. Same in france 6HP. but i have boat license. i m more affraid about insurance.