Shaft housing question -- galvanic corrosion? - SailNet Community
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post #1 of 5 Old 08-17-2013 Thread Starter
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Shaft housing question -- galvanic corrosion?

I have a recently purchased 32' 1949 Monk Classic Motor Cruiser, and am seeking some advice re; her shaft seal arrangement. She has spent a large share of her life in freshwater (Seattle area) but now is relocating permanently to salt water in Vancouver, BC.

My question is around what the correct solution to the likelihood of galvanic corrosion would be for her shaft seal fit-out?

From the survey: "Shaft seal gland: the hose clamps on the shaft seal are not 100% stainless steel, the screws are rusty and wasting. The seal is single clamped as best viewed. Replace the hose clamps at the next lift out. The shaft housing is bronze as is the gland. All the fastenings, nuts & bolts are stainless steel. Should the vessel lay in a salt water environment galvanic corrosion of dissimilar metals will no doubt occur."

My preference is to hold off until spring for her regular bottom coat, but I also don't want a problem with the seal between now and then. It is currently properly tightened and stable (in her freshwater home) to allow 6-8 drops of water per minute.

Two questions:

1. What is the best/proper practicable longterm solution (also considering cost)? and;

2. If it can be put-off until spring to implement the proper longterm solution, what should I do during the interim months?

Thank you folks,

Brian
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post #2 of 5 Old 08-17-2013
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Re: Shaft housing question -- galvanic corrosion?

Brian, do you have any photos of this problem?
I too am new to this boat owning thing. As near as I can tell to prevent further corrosion, the addition of a shaft zinc might do the trick- it could be installed by a diver and shaft zincs are not that expensive.
As far as the clamps inside, it kind of depends how far gone these clamps are. If they are in danger of imminent failure- you should haul now and get'er done now.

Good luck sir.

Last edited by mtitus; 08-17-2013 at 05:20 PM.
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post #3 of 5 Old 08-17-2013
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Re: Shaft housing question -- galvanic corrosion?

Brian,
ALL plumbing connections below the water line should be double clamped with 2 hose clamps. This is an accepted standard. At a minimum you should add another hose clamp to each connection where there is only one. Even better would be to replace the original hose clamps and add an extra one for each joint/join.

Pics of your current shaft gland would help.

Here is one of the best articles that describes how a traditional stuffing box gland is set up. There is little or no danger of galvanic corrosion with this set up:

Re-Packing A Traditional Stuffing Box Photo Gallery by Compass Marine at pbase.com

The rubber shaft log hose keeps the bronze stuffing box separated from the stainless steel hose clamps.
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Re: Shaft housing question -- galvanic corrosion?

It sounds to me like the surveyor is noting a potential long term issue. Typically if it's something of immediate concern they would give a deadline(eg. before use, within 30 days etc).
Next haulout to me would be the spring, unless you're planning any long trips. If it's single clamped right now, could you perhaps had a 2nd more appropriate hose clamp to each of the joints (for a total of 4 clamps), then switch the bad ones out for two new ones, staying at 4 total as required by insurance.

Last edited by Jgbrown; 08-19-2013 at 12:05 AM. Reason: Capital letters.
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Re: Shaft housing question -- galvanic corrosion?

Thanks for responding folks.

I'm going to crawl in and take a better look at the current set-up. I agree that the surveyor didn't seem to be suggesting immediate action, but am concerned that this was done before it was known that she is being relocated from fresh to salt water.

There are the usual collection of zincs installed, and a second set of clamps are being installed if they're not already there. I mostly want to make certain I'm doing what is necessary to protect the set-up through the Vancouver winter months. If it means I have to haul and deal with earlier to avoid damage, I'll have to get it done. Otherwise, I would prefer to wait until her spring painting.

Whatever advice you have is appreciated,

Brian
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