Short story: check for detectable resistant between motor’s 3-phase circuit and motor casing, and open up the motor casing if this is not open-circuit.
Long story: I thought a few of you might be interested in my recent e-foil motor corrosion experience. I have been successfully using two older-model Tame Billow e-foil for around 18 months, with relatively frequent use (1-3 times a week, most weeks) in the sea. For those that do not know this e-foil, it is one of the cheapest on the market … supplied by Anhui Yuhan Intelligent Manufacturing Group Co. (with email @yuhuan-med.com … I not sure why the difference … ). I have since changed the angle of incidence on the foils and made other intentional and some unintentional modifications, gone through a few hand remotes, etc. Seems all the usual stuff.
Back to my story … I have been hosing the e-foils down with fresh water after each use and storing in a dry garage between. A few months back, the black surface coating on the aluminium motor casing started blistering on both foils (you can see this in one of the photos below … this is after cleaning it up), with the coating falling off in places exposing corroded aluminium. This should have been a warning that something had changed I should have investigated further … but I didn’t.
I was then away for a few weeks. When I came back, the motor shafts on both e-foils had seized. Another warning that should have got me to check further before use.
I managed to wriggle the shafts so that they again turned, and the shaft soon seemed totally free and the motor/ESC/controller seemed to work normally, including on the beach, just before taking one of them into the water. Once in the water, I managed to get a brief burst of prop movement before all went quiet. I did detect a very small tingle when touching an area above the ESC, but didn’t think too much of this as it was almost not noticeable. This changed when I lifted the e-foil back onto the beach and prodding around and checking various things … providing a solid earth return because I was standing in a salt water-drenched wetsuit and with my feet still dipping their toes in the sea, I found the motor casing to have reasonable volts … a kick only to be beaten a minute later by the bolt that I received when I touched the outside casing of the ESC. The next step was to disconnect the battery using a very dry towel and waiting in case there were some powered up capacitors that I could also find.
The photos below show what I found on taking the motor apart. Rust and a little too much salt water. And so started the process of cleaning this lot up, on both e-foils. This included:
• Removing the coil on the worse one and washing it is soapy water, then fresh water, then baking at 60oC in the oven until my partner came home and found it … I guess it wasn’t food grade!
• Wire-buffing the shaft and inner motor section to remove corrosion.
• Scrubbing the inner surfaces in the motor cavity with a range of “instruments” including toothbrushes, screwdrivers and steel wool pads to remove corrosion and corrosion-related films. I checked how good my efforts were with an ohmmeter … anything less than open circuit of the windings and the body sent me into another cleaning cycle.
• Replacing the motor bearings.
• Replacing some of the motor assemble bolts … one which broke due to corrosion during motor disassembly.
• Cleaning up all threads with die and tap.
• Easiflowing the electrical connectors of the removed coil (as my thinking was that solder would be too low a melting temperature).
• Assembling with liberal grease where it should be, new o-rings, and smearing all o-rings and o-ring joints with Ray-Tech Magic Gel 1000 (fantastic stuff … what a find this gorilla snot has been).
• Filling in external nut cavities with Ray-Tech Sky Plast (a two-pot putty … another gem) aimed at lessening the drag.
• Replacing the ESC on the e-foil I took into the water … this had obviously failed … the benefit of having two e-foils is that you can swap parts as an easy check to see what seems broken).
On the latter, I ordered a replacement ESC from @yuhuan-med. US$365 + US$185 shipping (to NZ) … and they also sent the power and remote transceiver connectors for the ESC, and even the solder to connect them up … this connection step needs to be done after you put the ESC in place and hence not done at the factory.
All now works.
But here are the lessons:
• In the failed mode, there was resistance between the three phase motor wires/connector and the casing of the motor. I would have been able to see this had I checked this with an ohmmeter … alerting me to likely water ingression, etc.
. Now looking back, I would have detected some resistant (i.e., and not open circuit) had I checked the ESC 3-phase wires vs the motor casing really early on … the failure mode was likely sea water entering the motor cavity and pulling apart way back when it first started would have saved a lot of work.
From time to time I will now check that the three phases are open circuit with respect to the motor casing … and open the motor up should status this change.
• The blistering and corrosion on the outside of the motor casing is also an indicator of far deeper corrosion … if you have corrosion on a yacht, you check the anodes, then the motor seals, etc. Same should be for e-foils.
Hope this is useful to someone out there. I’m happy to be on the water again … and the with open-circuit three-phase wires relative to the motor casing 
