Replace zinc now, or no?

peaman

Member III
Motoring out from the marina today for a sail, a strange sound came from below. At 2 second intervals (at 1300 rpm or so), we heard maybe 4 taps within a 1 second period. Once we got into open water, I dropped anchor to take a look. I had a single zinc on the prop shaft between the shaft log and strut, and it had come loose one one side and the two halves had shifted diagonally. Fiddling with it between breaths, a screw fell into my hand and I was subsequently able to loosen the other screw, and then to remove the zinc.

The zinc was in fair shape, with much less than 1% of its weight lost after 3 months in the cool New England sea water. So the question is, would I be foolish to not replace the zinc until after the boat is hauled for the Winter in 3 months time, or should I rush to arrange for a diver to install a new one soon? The prop, strut, and shaft (except under the zinc) were all coated with bottom paint before launch.
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
Motoring out from the marina today for a sail, a strange sound came from below. At 2 second intervals (at 1300 rpm or so), we heard maybe 4 taps within a 1 second period. Once we got into open water, I dropped anchor to take a look. I had a single zinc on the prop shaft between the shaft log and strut, and it had come loose one one side and the two halves had shifted diagonally. Fiddling with it between breaths, a screw fell into my hand and I was subsequently able to loosen the other screw, and then to remove the zinc.

The zinc was in fair shape, with much less than 1% of its weight lost after 3 months in the cool New England sea water. So the question is, would I be foolish to not replace the zinc until after the boat is hauled for the Winter in 3 months time, or should I rush to arrange for a diver to install a new one soon? The prop, strut, and shaft (except under the zinc) were all coated with bottom paint before launch.
I've had them fall off too, which got me in the habit of swimming down to tighten the screws sometime midseason.

I don't think 3 mos w/out a zinc is going to hurt your boat since you said the zinc didn't shed much. OTOH, it's pretty easy to install or tighten one yourself with a pair of swim goggles and a T-handled Allen wrench. Tie the wrench to your wrist with a string so you don't lose it.
 

Pete the Cat

Member III
Just a pointer from this former boatyard worker. If you do not want your zincs to come loose or fall off be sure to hit them with a block of wood (we had a wooden hammer) after you do the first tightening and then tighten them again. if you haul for the season, clean the shaft and replace the zincs in the fall before it is put away and tighten them as the last thing you do before you splash the boat.
 

Frank Langer

1984 Ericson 30+, Nanaimo, BC
Pete,
I've heard that before from yard staff. I replace my zincs, often with the boat in the water. I tighten the Allen screws as tight as possible, and then dive a few days later to try to tighten them some more. As they begin to wear away I tighten them again from time to time as I'm swimming.
Is there a trick like hitting them with a wooden block or rubber mallet that would work under water when I first replace the zincs?
Frank
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
I tried the wood block trick once when the boat was on-the-hard, but couldn't bring myself to smack it hard enough to ever allow me to get the screws any tighter. Instead, I discovered that if I re-tightened the screws every couple of days, they would accept an additional 1/2 or 1/4 turn each time over a several day period. I'm guessing that maybe the zinc deforms a little bit over time allowing the screws to be tightened further until the zinc reaches its "final" shape. Which, like Frank said, might mean further tightening after it decomposes a bit.
 

RCsailfast

Member II
I wonder if you are getting corrosion between the stainless screws and the anode. I put marine grade antisieze liberally on the screws when installed. Never a problem with coming loose and easy to replace. I also lightly sand the inside of the anode before installing to get the best connection to the shaft.
 
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