Mixed metals dilemma

rjp

Member
Joined
29 Apr 2004
Messages
462
Location
North Wales
Visit site
When I was refitting my Buchanan sloop I found that twin cockpit drains had been merged into one outlet as the fitting of a new engine by the previous owner had interferred with one of the original outlets. At the time I wasn't too bothered, but because I found the gatevalve on the remaining drain totally seized, I decided to replace it with a ball valve and thought I may as well replace the skin fitting at the same time. I obtained all parts via the website of a well known supplier and thought I was being quite careful. Ball valve and hose tail were in DZR, but no skin fitting could be found in that material, so I chose one described as bronze.

Thinking it would be a good idea this year to add a second outlet, albeit in a new position, I thought I would just reorder what I had bought previously so I dug out the old order and put the part numbers into the website search facility of said supplier. Apart from a shocking increase in price over 3 years, everything was fine except that I noticed that the description for the skin fitting now said ATD instead of BRZ, so I phoned up to enquire about the difference. The reply was that ATD is mixture of metals and shouldn't really be used below the waterline - 'use gunmetal instead'. So far so good. But had the type of metal for the same part number changed during the 3 years or so since I had purchased the last one? 'I doubt it' was the reply, 'We've probably just updated the description'! So it looks as though I might have a dodgy combination of metals below the waterline. Logic says not to worry, Alysia has only spent 4 months in the water last year and if she goes in in two weeks as planned will be lucky to see 5 months this year - I can't see dezincifcation or galvanic corrosions being a problem over that kind of timescale, particularly as I'm on a swinging mooring well away from stray currents etc. So maybe change it next winter.

Does that logic seem reasonable?

John
 

rikgraham

New member
Joined
13 May 2007
Messages
3
Visit site
I saw electrolosys go through 8mm of galv steel in two seasons when combined with a bronze bolt. De-zinced brass has about the same strength as Aero try the hammer test before launch.
 

Bajansailor

Well-known member
Joined
27 Dec 2004
Messages
6,461
Location
Marine Surveyor in Barbados
Visit site
I would agree re the hammer test - give it a really good wallop soon, and if it disintegrates, well, you need to replace it!
If it doesnt, it should keep going for a bit longer - but I think the bottom line would be 'if in doubt, replace it' at some stage.
 
Top