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Corrosion of brass nipple

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Sep 1, 2014
83
Beneteau 37DK Alameda
I sail a 2011 B37. The feed for the stern tube water is on the back of the heat exchanger. The exterior of the nipple has blue corrosion (see photo ). I cleaned off and used WD40. It seems solid, so did not replace the part. I know the feed on other Beneteau boats are different. Stern tube nipple is good. Have any of you sailors had this issue? You always seem to have the answer!
 

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Jan 4, 2006
3,822
Hunter 310 West Vancouver, B.C.
Looks like a very small leak at the HEX outlet which is promoting surface corrosion on the hose X NPT adapter.
If you're really concerned about excessive corrosion in that area, scrape away a small area on both the HEX head and the adapter and see if you expose brass coloured metal (99.99% prob.). If it's spongy pink (0.01% prob.) lot's of further investigation required.

Do I understand you to say that the discharge of the HEX feeds into the stern tube ? Odd. Or do you mean a mechanical shaft seal ?

The feed for the stern tube water is on the back of the heat exchanger.
 

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Sep 1, 2014
83
Beneteau 37DK Alameda
The tube is attached to the standard Beneteau fiberglass stern tube. This system eliminated the need for a thoughull. No modification of factory installation. I will scrape and hope for pink! I can always just replace and seal the new part. Thanks
 
May 17, 2004
3,430
Beneteau Oceanis 37 LE Havre de Grace
Do I understand you to say that the discharge of the HEX feeds into the stern tube ? Odd. Or do you mean a mechanical shaft seal ?
Beneteau’s of that era have two outlets from the HX. The primary outlet goes to the exhaust like normal. This second smaller one goes to the stern tube. I presume it’s there to help lubricate the cutlass (integrated in the end of the tube) and to prevent air locks against the Volvo shaft seal.
 
Jan 4, 2006
3,822
Hunter 310 West Vancouver, B.C.
This system eliminated the need for a thoughull.
I don't know if that's ingenious or not :rolleyes:. It's just so unusual, takes a bit of getting used to. As @Davidasailor26 said, keeps the shaft seal wet at all times.

I will scrape and hope for pink!
No, hope for a shiny metallic yellow colour. A spongy pink colour indicates a zinc rich alloy which is baaaaaad for corrosion. 99.9% sure yours is low zinc brass which is suitable for marine use.