supersailor
Contributing Partner
My first Try to get this message through on the site resulted in it suddenly disappearing from the screen. Searching around did not find it. This is the third time this year that this happened.
Those pictures show an awfully large amount of electrolysis on the prop shafts. That is enough to be worrisome. We have "hot" marinas and, I think no truly "cold" marinas. The one I'm in is definitely hot. The source of the stray currents can be other boats or drooping lines under the dock that go underwater. A brand new Westport 120 pulled into a guest dock next to me. Within a short time, the slug of zinc I have on the stern quarter when docked cleared itself of all the marine growth it was sporting. Shortly after, the vinyl covering the grounding cable cleared all the growth also. The lesson here was "It is not only the old wrecks that leak. It can be any boat in the marina.
The very best protection would come from unplugging. Not practical for those of us who insist on having refers, freezers and electric heaters. The attached photo is not of propulsion equipment but of the back of the windlass power switch two weeks after Terra Nova suffered her partial immersion. The side terminal that's almost gone is the hot side. The switch was off so the other side was dead. The difference between the two is sobering. These same forces are at work on your prop, shaft and strut. Because the prop etc. are bronze, they don't get eaten up as fast as the brass does but eaten up they do get.
I use two prop zincs, a zinc slug attached to the negative ground, and a galvanic isolator. The prop zincs used to last about five months, now the look good after a year. Probably it is both the zinc slug and isolator working together that' s doing the trick. Whatever, I'm happy with the results compared to the performance prior to them.
Those pictures show an awfully large amount of electrolysis on the prop shafts. That is enough to be worrisome. We have "hot" marinas and, I think no truly "cold" marinas. The one I'm in is definitely hot. The source of the stray currents can be other boats or drooping lines under the dock that go underwater. A brand new Westport 120 pulled into a guest dock next to me. Within a short time, the slug of zinc I have on the stern quarter when docked cleared itself of all the marine growth it was sporting. Shortly after, the vinyl covering the grounding cable cleared all the growth also. The lesson here was "It is not only the old wrecks that leak. It can be any boat in the marina.
The very best protection would come from unplugging. Not practical for those of us who insist on having refers, freezers and electric heaters. The attached photo is not of propulsion equipment but of the back of the windlass power switch two weeks after Terra Nova suffered her partial immersion. The side terminal that's almost gone is the hot side. The switch was off so the other side was dead. The difference between the two is sobering. These same forces are at work on your prop, shaft and strut. Because the prop etc. are bronze, they don't get eaten up as fast as the brass does but eaten up they do get.
I use two prop zincs, a zinc slug attached to the negative ground, and a galvanic isolator. The prop zincs used to last about five months, now the look good after a year. Probably it is both the zinc slug and isolator working together that' s doing the trick. Whatever, I'm happy with the results compared to the performance prior to them.
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