I have been doing some digging into the use of brushless out runners. The Open ROV teams use these extensively for their thrusters. Many operate them without any modifications and just replace as needed but others go to a little more effort and use potting compounds to help prevent corrosion. The motors work fine in fresh water or salt water but the bearings will seemingly corrode first and other components over time. The windings themselves are insulated of course but can gradually get damaged by silt etc.
Good thread on their forum here,
http://www.homebuiltrovs.com/rovforum/viewtopic.php?f=3&t=1762&start=20
So, I think it is worth a shot to test out the 3D Printed Hydrofoil using a relatively stock out-runner. It would require no gearbox and no complicated enclosure.
Alien Power systems do some nice low kV out-runners. It would just require finding the right prop. So at the moment the component list I have in my head would be,
60kV out-Runner
http://alienpowersystem.com/shop/brushless-motors/alien-6374-outrunner-brushless-motor-60kv-3200w/
Banggood Transmitter & Receiver
https://www.banggood.com/2_4GHz-Rad...ectric-Skateboard-p-1125575.html?rmmds=search
Red Brick 200A ESC
https://www.banggood.com/Red-Brick-...PTO-NO-BEC-200AOPTO-p-77974.html?rmmds=search
UBEC
https://www.banggood.com/DC-DC-Conv...or-RC-Airplane-FPV-p-981978.html?rmmds=search
2 x 5S 5000mah batteries (connected in series)
https://www.banggood.com/ZOP-Power-...Battery-XT60-Plug-p-1032689.html?rmmds=search
XT60 Series Connector
https://www.banggood.com/XT60-2-str...atteries-in-Series-p-915639.html?rmmds=search
Total cost around £200
More than enough power to get foiling (3200w is the peak power) will need less once up. That will give around 2200 RPM running at 10S. I am still hopeful that the 80kV in-runner that Alien Power Systems is releasing soon will be a better solution but suspect it will come with a hefty price tag.
I'll definitely be risking the out-runner with this approach but its not too expensive an experiment. I will need to work out the best prop to use though so suggestions welcome. It will be 2-3 weeks before I can test as still need to laminate the foil and wait for parts.