Seacocks, through-hulls and skin fittings
Every hole in the hull is a way for water to enter. Each seacock must work, be made of a suitable metal, and be fixed to the hull securely.
Updated 2 min read
Key points
- Operate every seacock. A seized one is a failure.
- Pink or crumbling bronze fittings show dezincification and need replacing.
- Hoses to seacocks are double-clamped, with a softwood bung nearby.
Why they matter
Seacocks and through-hulls let water in and out for the engine cooling, the heads, the sinks, the bilge pumps and the cockpit drains. A failed one below the waterline can sink a boat. Most surveyors check every one.
What to check
- List every opening at haul-out and match each to a valve inside.
- Operate each valve fully open and closed. It should move with a hand, not a wrench.
- Look at the material. Bronze and DZR (dezincification resistant) brass are standard. Ordinary brass dezincifies in seawater and turns pink, brittle and porous. Reinforced plastic fittings such as Marelon are accepted if they are in good order.
- Look at the fixing. A seacock should be bolted or screwed to a backing plate or a reinforced base. A fitting held only by the hose is not secure.
- Check the hoses. Each one has two stainless clamps, no cracks, and is rated for the use.
- Look for a softwood bung tied near each valve, for emergencies.
Types
- Ball valves are common and lighter. They can seize after years with no use.
- Tapered cone seacocks are traditional and need greasing.
- Gate valves are not suited to below-waterline openings, because they can fail without a visible sign.
Skin fittings above the waterline
Cockpit drains, bilge outlets and exhausts above the waterline still need hoses and clamps in good order. A hose that is under water when the boat heels is below the waterline in practice.
When to replace
There is no fixed life, so judge by condition. A valve that is stiff, corroded, leaking at the spindle, or made of unsuitable metal should be replaced. Many owners replace them at a refit in a boat of 15 to 20 years.
Cost
A valve costs little. The labour and the haul-out are the expense, which is why a survey that lists a dozen fittings changes the price. See How to read a survey report and cost the findings.
Related guides
General information, not legal, tax or financial advice. Rules change; check your own case with a professional or ask us.