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KiwiSkipper 05-07-2020 02:51

Possible Calcification on Prop-shaft ??
5 Attachment(s)
Hi .. Looking for anybody who can help with suggestions on this issue.
Back story -- I picked up a submerged mooring line or similar leaving the marine. It wrapped and bent the shaft.
Local Marine engineer had the shaft replaced. Also fitted new bearings (rubber type)
During the process..he smashed the bronze cast housing at the engine end of the stern tube. It housed a white metal bearing. When it was replace/remade, the decision was made to fit a rubber bearing in place of the white metal bearing.
The whole system was reassembled and went back into the water as normal.
The problem surfaced about 4 weeks later when I went to back out of the marina. The shaft made a horrific noise. I call the engineer who listen and then removed the boat back out of the water. He thought something had come loose.
Upon removal was discovered that a film of calcification had formed on the shaft inside the bearing areas.
It was clean off .. polished and put back together.
I wasn't there but apparently it was back to being silent. (no noise)
My next visit to my yacht (about 7weeks later) I was alarmed to hear the same ..and possibly worse noise from the shaft. The Engineer says ..not his issue!
The yacht had been in the same berth with me as owner for 4 years and for the previous owner ... for 10 years. Never had calcification issues before (with the old shaft)
Has anybody had experience with this. ?? I'm wondering if its an electrical issue now that the shaft is isolated with the rubber bearing replacing the the white metal one.
Boat is currently unusable as the calcification is ripping the cutlass bearing to shreds.
Attached photos of the system assembled and disassembled showing calcification.

KiwiSkipper 06-07-2020 15:04

Re: Possible Calcification on Prop-shaft ??
Wow .. I'm shocked .. not one reply in days. This must be rare indeed!

slug 06-07-2020 16:23

Re: Possible Calcification on Prop-shaft ??
Might be metallic deposits originating from your zinc anodes

That section of shaft seems to be the only exposed , wet , metal under the water

Examine any wet metal under water for similar deposits

Check your boat for electric leaks

KiwiSkipper 06-07-2020 16:35

Re: Possible Calcification on Prop-shaft ??
Hi .. Thanks for the reply. I will indeed check the boat for other deposits. Seems strange that this has happened at the same time as the shaft was replaced?
Any thoughts on where electrical leaks might originate? There is only 12v on the boat permanently.... and this is shut down when I'm not there. I use 240V marina power at times using a double insulated cord connected to shore power. Only when I there also.
Do you think the shaft should be earthed ?? Would the shaft being isolated create the best place for zinc to be deposited? :confused:
Cheers for the help

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