Sea Cock Replacement

I was so lucky!

I recently had my boat, the Blue Dolphin, hauled out to have the bottom painted and the sea cocks replaced. What I found really scared me and it might scare you too. This boat was built in 1970 in Sweden, 39 years old. Sea cocks were probably original. I have had the shipyard check all the sea cocks each time the boat was hauled for bottom paint…all reported OK. (They did look fine from the outside…well not really…look a little closer!) This time however, I felt that it was time to have four unused sea cocks removed and sealed with fiberglass and four others replaced with heavy duty, flanged, bronze sea cocks. When the old sea cocks were removed, a close examination revealed severely deteriorated thru hull fittings with pits throughout the metal and de-zincified (pink) areas. Even though the outside looked fair, the inside looked like “sawdust” and it seemed like a slight pinch with your fingers would collapse them.

I urge all boat owners to examine your sea cocks for signs of corrosion, de-zincification, clamps etc. If your sea cocks are very old, they are probably the old style “gate” type and should be replaced with “Ball cocks”. The best type is the flanged type with a stainless steel ball cock and lever. Beware of sea cocks with a chrome plated brass ball cock which will corrode in salt water, a stainless steel ball is best. The “flanged” type has the advantage-tage over a straight thru-hull of greater support on the hull and cannot be twisted which can disturb the sealant.

I am happy to report that the Blue Dolphin now has four new bronze/S-S heavy duty sea cocks, no unused penetrations, and has been surveyed by Capt. Alain Vilage with a clean bill of health. We should be good for another 39 years. Can you say that about your boat?

Large valve replaced in a more accessible location

Small unused valve removed and hull sealed

Metal did not look too bad from outside and when scraped with

a knife blade showed good brass color.

Metal completely corroded inside. Pink color indicates

de-zincification. Ready for failure!

Pieces of the thru hull showing corrosion completely

thru the metal walls and pink colored.

Two of the 4 new valves in-stalled. Flanged valves bolted thru with backing plates of marine plywood and sealed with 5200.

Double clamped

A couple of styles to choose from. One must also be careful to use the correct threads when fitting these elements together. NPT and NPS threads are not compatible. A good source of information on the correct installation can be found at: http://www.groco.net/

See the Technical Service Installation bulletins for details on threads and installation methods.

Remember: It is your life and your passengers lives that may be at stake. Pay careful attention to these details