Seacocks "pinked out" on a Swan 47
While servicing the seacocks on Outrageous it was noted that they were turning pink indicating gradual need of replacement. Has anyone else experienced similar issues with S&S Swans of similar vintage (1979)
Outrageous 47/039

Please see thread in this section dated 29 September 2009

Fair winds!

matteo (38/067 Only You)

Thanks!

Dear all
Would appreciate to hear if somebody has similar experiences. At first thought it appears unlikely that the seacock alloy would change its properties with the time, and that some external change has caused the corrosion. Warter containing new pollutions, or lubricating the seacocks with unsuitable grease?
Kind regards
Lars

Dear Professor,

I replaced all of my seacocks; although I did not notice any "pinking," the bronze through bolts had weakened to the point that very little torque snapped each one.

The seacocks themselves, although old and seized, did not look too bad.

Chris Mabel's Casse Tete 43/003

Dear Chris
You say through bolts, this indicates that they have been installed later, and may have been of a different material. The original installation was flush on the outside without bolts, this was important for racing. The seacock was held in place with laminate over the inside flange.
A general recommendation for sea cocks would be to test their strength whenever the yacht is ashore. Use brute force to bend and twist them, even if they look perfectly OK. If there is a hidden problem it is much preferable to detect it in this connection, and not at sea in hard weather.
Unfortunately it can not be determined whether the material is bronze or brass by its appearance. Even if it should be brass the dezincification takes place slowly, and if the recommended testing shows proper strength it is unlikely that something will happen during the next season. This assumes the yacht is lifted at least once a year.
Testing can also be done in the water if you take care to cover the hole on the outside so no catastrophic leak can occur even if the sea cock should fail.
Kind regards
Lars

Dear Professor,

Yet another surprise with my boat!  The seacocks were definitely glassed in AND through-bolted.  This must have happened after the boat was seized and refurbished.  As you already know, there are a lot of changes that are not in keeping with the original nor with good practice.  Time will cure all these!

Chris

Dear Lars:

When I took ownership of Swan 43/46 "Hiro Maru" I replaced all of the thru-hull valves as a precaution. Two of the thru hulls did have similar issues where the tapered bronze valve face surfaces exhibited some pitting and also a "pink" color. I do not know the age of these units but they were of the type with the valve base flange glassed into the hull without any mechanical thru-hull fasteners. These thru hull valves were replaced with similar new units approximately 12 years ago and appear to be OK based on annual out-of-water dis-assembly and inspection.

I know that in our sailing area we often encounter stray electrical currents in many of the harbors which appears to accelerate electrolysis issues between dis-similar metals. All boats in our area incorporate sacrificial zinc anodes on the propeller shafts. Many (including myself) also drop a second zinc anode over the side of the boat attached to a heavy gauge cable grounded to a shroud chain plate.

Fair winds,

Hiro Nakajima

Pinking is due to galvanic corrosion between the copper and tin of the bronze alloy. The tin disappears leaving the copper behind seriously weakening the fitting over time. After 30 years it is undoubtedly high time to replace the through hulls.

Bonding the through-hull together electrically and attaching the bonded set to an extrnal sacrificial anode will slow or stop the reaction, but will not undo the damage done.

I replaced all the Blakes throughhulls first thing after purchasing my 41.

John