Seized seacocks: how surveyors check through-hull valves and what replacing them costs

A seacock is the valve between the sea and every hose that runs below the waterline: engine intake, heads, sinks, cockpit drains. If a hose splits or a strainer cracks, closing the seacock is what stops the boat filling. A seacock that won't close isn't doing that job, which is why surveyors put it in the safety section.

How a surveyor checks them

Each handle is worked through its full travel. A stiff handle gets noted, a seized one gets an A. The surveyor looks at the body and base from inside for corrosion product, weeping and the hose clamps, and from outside at the through-hull fitting itself. A fitting that has turned pink has lost its zinc, usually because it was brass rather than bronze, and is weaker than it looks.

Then the type. A proper seacock has a flanged base through-bolted to the hull, ideally with a backing block. A ball valve threaded straight onto a through-hull looks similar but leaves the threads taking any knock or load on the hose.

What the standard asks

ABYC H-27 covers seacocks and through-hull fittings. In our words: seacocks must be readily accessible with handles easy to operate, made of corrosion-resistant and galvanically compatible materials, and installed so that the assembly holds a 500 lb static load for 30 seconds. MarineHowTo tested threaded combinations against that figure: a 3/4 inch bronze valve on a matching through-hull failed at 404 lb, and a 1 inch combination at 458 lb.

What replacement costs

The boat has to come out for any through-hull work, so replacing all the seacocks at once costs little more in lift and storage than replacing one.

Photos to take

Each seacock with its handle visible, a close-up of any corrosion at the base, the through-hull from outside, and a label photo if there's none. With Axsail, say "seacock, engine intake, seized open" while you take the photo and it lands on that finding.

Writing it up

Name each seacock by what it serves and where it is, say whether it operates, what the body and fitting look like, and whether it's a flanged seacock or a valve on a through-hull. A count helps: "6 seacocks, 5 operate, 1 seized" tells a buyer what to budget for.