@Gobbla Have you been inspired by this post ? http://www.efoil.builders/t/builders-how-not-to-drill-your-alu-or-carbon-mast/112
wood floor skirting solutions on the internet: PVC flexible skirting band, 10USD for 20 metres with 3M adhesive
I am fascinated by your metal work. My 3D printed parts look quite cheap in comparison 
May I ask why you built such a long tail, as the shaft to the prop is consequently very long and may accentuate vibrations ?
@SoEFoil, yes i take some ideea from this post, and adapt it to my round cable
@philgib i have made long tail to avoid turbulence before proppler.
At high speed for me it will reduce efficency of proppler.
I did not make calculation to define the best length
some of my inspiration :
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I would try to make much more room for the motor cable solder joints. Mine ended up about twice as thick as the cables because I had to make them waterproof. They are also very stiff.
I like the counter rotating propeller 
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Yes ! We need to make this! Pefect way to complicate things!? Started planning some months ago and orderd some gears and bearings but the project died a little.
Any one want to join in with CAD and R&D
We can do a open source build on the forum?
Efficiency of the system may be improved slightly, but it also removes the torque generated by a single prop drive. But most importantly it looks super COOL!
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2 propellers turning in the opposite direction on one shaft ? It is going be complicated for the gearbox… N6 and hollow shaft… It is crazy !
Yes two props on one shaft.
can be done this way
(red shaft is hollow)(green gear is held in place)
same as in the torpedo drawing. Will have to so something clever stuff with the seals and bearings.
Cool, I am in
Would it make sense to include the reduction at the same time?
Not possible for me ,blue same speed as red
For gear réduction , it will the same a car , propeller in front and in back , motor at 90 in line with mast …
Both are the same speed but turn in opposite directions. Anyway as awesome it is, as much it is in sealing manufacturing etc. twice as much effort.
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?