I have read the excellent posts in this forum on this topic but not found any that specifically address my situation so I am asking for assistance.
I have a fiberglass
boat with 4 unbonded bronze throughulls. 3 have minor green patina growing from the bottom up. The fourth is behind the head
and is heavily corroded all over. The threads are all gunked up with green as well, but after cleaning
with sandpaper, the metal appears to be bright yellow and there is no pink or white flaking. Any ideas why there is so much corrosion
on this one?
When I hauled the boat last week, there was a 12" square patch of galvanic burning on the hull
around the bronze strut. It is my understanding that the grounding plate is part of the strut where it is through bolted into the hull
. It was blistered and the paint bottom paint
had flaked off in that one area. The yard foreman said it was galvanic burning and he asked me if there was a green wire connected to the prop shaft. We sanded off the paint
and applied new bottom paint
I checked and found a connector attached to a bolt on the grounding plate, but there wasn't a wire attached. I also checked the grounding lug inside the shore power
circuit breaker box and discovered that the green wire for the AC ground had been disconnected. I re-connected it, but have not yet installed a green wire going between the AC ground lug a bolt on the grounding plate bolt. I bought Don Casey's book on Simplified Sailboat Electronics
and read up that the green wire on the prop shaft connects your boat to other boats in the marina and is an entry point for stray current
When I hauled the boat 3 years ago, there was no sign of any galvanic burning on the hull. Since I hauled the boat, I installed new batteries and and a battery charger
. Now the boat is connected to shore power
when it is at the dock
. I also just bought a little heater for mold
control. I am wondering if being plugged in all the time s the reason for the galvanic burning and the advanced patina on the one through hull?
I did some of the tests that Casey suggests in the book. I did not get a reading when I tested for stray current
in the water
. I did get a reading of 1.8v when I tested for AC current between the ground and neural sockets on the boat. I then tested the 30 amp socket on the dock
and got the same reading, so the dock wireing seems to be the source of that problem. I am not sure what to do about that or if it is a problem.
Possible solutions that I have come up with are:
Unplug the boat from shore power and use solar panels
to charge the batteries. Plug
in the heater I use to prevent mold
directly to the shore power cord using a pigtail adaptor, OR install a Galvanic isolator
, which would be more convenient and useful for when I wanted to recharge the batteries quickly or run the electric
heater when my wife is on board.
Buy or make a "Zinc Fish" and connect it to the ground plate.
Install a green wire between the ground plate and the AC ground.
I would be interested in hearing from anyone who can address these issues. I have learned a lot here over the years and always appreciate feedback.
Happy Holidays to All,