C-32 CB Stern Thruster

[pshastings]

2020 C-32 CB stern thruster actuates and runs (and thrusts) for a couple of seconds, then blows the ANL fuse. This failure is repeatable.

I disconnected the solenoid and the fuse didn’t pop, so it’s either the motor or something electrical when it draws load.

Both fore and aft bilge pumps had failed so the motor housing was half-submerged for some time. (That problem has been fixed.) But when the motor actuates (before blowing the fuse), it runs seemingly normally (i.e., no apparent binding, definitely not locked up).

Last time a diver cleaned the bottom, he verified nothing in the thruster tunnel and thruster prop turned freely.

The mechanic is afraid that if he pulls the motor he’ll flood the boat. I find conflicting reports on the interwebs.

There is a fair bit of corrosion in the wiring and the cavity that holds the motor did have a good bit of water.

The bow thruster works fine and the battery is new, so I don't suspect that as a cause.

Questions:
(1) Is it safe to remove the motor while the boat is in the water?
(2) Is corrosion in the wiring a likely cause?
(3) Am I missing anything?

(As an aside, tugnuts won't support new tags. Suggest adding "stern thruster" and "lewmar" to tags list.)

 

[SKing]

If the motor runs you have 2 major suspects.

Either you have physical resistance to movement causing high current draw. This could be bearings, gear box etc. Check how easily the blads spin by hand. Anything that keeps the motor from spinning at full rpm causes higher amperage draw.

Second you could have bad connections causing the voltage to be low at the motor which causes high current draw, blowing fuses. Any reduction in voltage means the amperage increases. Check all connections. If wires were submerged at the connections the wire or connections may be corroded.

If the water entered the thruster housing I personally would condemn the thruster assembly. If you are paying for someone else to work on the boat it is probably cheaper to replace the whole assembly out of the water vs potential multiple attempts at replacing individual parts.

 

[pshastings]

Thanks; mechanic found a 2-volt drop at one of the lugs - comporting exactly with your scenario #2 - so with any luck cleaning up the (substantial) corrosion will cure the problem. Will update as things progress.

Incidentally, the motor casing was about 1/3 submerged for awhile, but no clear signs of water intrusion, and motor "sounds" healthy until fuse blows. Fingers crossed...