Calling all bonding experts?

[Sailingmd]

Sabre 28 #553 with Westerbeke W13 experiencing accelerated corrosion over past year.

1. No new electronics/electrical equipment.

2. She's not in a marina.

3. Currently on the hard and attempting to isolate problem.

4. Some discoloration in little "splotchy" areas over wet side of prop and shaft. THIS IS WHAT TIPPED ME TO POSSIBLE ELECTROLYSIS. Although-the zinc is being eaten at what apprears to be a normal rate.

5. Measured resistance between shaft and engine block...infinity. The coupler seems to be the culprit and it's NOT flexible.

6. The PSS shaft seal has no bonding wires. I also do not see any bonding straps connecting each side of the coupler.

7. Yes, from all accounts this is NOT THE CORRECT electrical distro according to sabre manual. Engine block should be less than 1 Ohm to shaft...or zinc on end of shaft for that matter.

8. I'd like to take care of this prior to launch-although Nigel's book is directred at in water troubleshooting. I'd rather deal in ohms when talking resistance-but I may be wrong.

What are my possible solutions? Not a fan of the brush as it will require constant wear (with rotation) and eventually fail. Bonding straps of similar noble metal around coupling collar should work. Like say one or two (for balance 180 deg out) bronze straps....help

[Sabreman]

Try to isolate where the circuit went open. Test resistance on the shaft (2 probes on the shaft). Should be zero. Put one probe on the coupling. Should still be zero. Keep moving away from the shaft toward the block and see where the circuit goes open. May sound obvious, but make sure you're testing clean areas - no paint, grease, dirt, etc.

It's possible that the 4 coupling bolts are so dirty or corroded that there isn't a good electrical connection (I don't mean to impugn your engine housekeeping, but your hull number indicates an older S28 - I had #521). It's quite possible that you aren't making good connectivity. As an aside with the Sabres bonding each through hull to ground, once in the water, you should have a zero reading.

Since the boat is out of the water, is it possible that it's just weathering? Regardless, I'd work on that infinity reading for now. Good luck.

[Sailingmd]

Thanks for the rapid response. Yes, she is an older boat. But she is newer than the S30 #004 that I previously owned...

As to the point at which the open occurs. It is at the coupling. I will inspect further to see what oil there may be in the coupling itself or in the bolts. I will also be installing bonding straps across the coupling. Will take photos and post pre and post.

Thanks again...

Shane