- This topic has 3 replies, 3 voices, and was last updated 12 years, 9 months ago by
.
-
Posts
-
We’re currently sitting on the hard, working on Rainshadow’s seacocks. The galley sink drain still had the original (failed) gate valve, and the custom bronze tailpiece that acted as a transition from the gate valve threaded connection to the 3/4″ drain hose. This is all just below the waterline on the port side – inside the galley locker.
While removing the gate valve, we put a modest amount of pressure on the bronze tailpiece – and it snapped off! The breakline was terribly pink (deep red, actually) indicating complete loss of zinc.
Had we dropped something on this in the galley locker and it snapped off while in the water, we would have a terrible problem -failed gate valve and broken tailpiece all below the waterline!We are finding that the original thru-hulls and seacocks are OK – so we don’t have a terrible galvanic corrosion onboard – it must just be that the metallurgy of these custom tailpieces left them subject to corrosion, especially when below the waterline.
So – if you still have the original tailpieces, check them closely. Besides this galley location, we have them in the head sink drain and bilge outlet drain. Maybe there were some on the cockpit drains too? (Those have been removed on Rainshadow already, but the PO gave us them while cleaning out his storage locker.)
Thanks for the warning. Harlequin is coming out this month for antifouling so it is a good time to check. I’ve no doubt mine are in the same condition.
Yes, indeed this is always a very important point to look at very carefully but…how do you do that ?
I ‘ve just the same question about the standing rigging.
Everybody agrees on the fact that you must change the seacocks or the standing rigging as soon as they appear to present some weak points. But I wonder how to make that kind of verification. I suppose a lot of people just change them when they are 15 or 20 or 25 years old; or if they show any visible failure. But, what about the invisible parts. Is there a way to analyse those pieces ‘scientifically’ ?Thanks in advance for your enlighted advices.
This is an excellent question, Jacques-Paulus! The short answer is – look for corrosion. But with crevise corrosion, it can be very difficult to see how bad it is, unless you do destructive analysis (or at minimum exploratory analysis). We pulled some chainplates, and found crevice corrosion that looked like small pits on the surface. Using a rotary tool to grind through, like a dentist would with a cavity, we discovered those small pits became ~ 1 cm long cracks that ran along the length of the rod, about 1mm under the surface.
Regarding the tailpieces, we should be able to give better hints about what to look for because we have the failed part in hand. Van and I will do some analysis of the break and repost.
I do need to correct myself though – those tailpieces are not bronze; they are copper, or at least a very copper rich alloy. So this was not likely to be a zinc-loss galvanic corrosion problem.
- You must be logged in to reply to this topic.