What Is a Seacock (Kinistin)?
The gate to every seawater inlet and outlet below the hull — a valve left unused is a valve that will fail when you need it most.
A seacock (kinistin) is the valve that opens and closes every inlet and outlet below the boat’s waterline (engine cooling intake, toilet, sink drains). In an emergency, it is the only thing that will stop water coming in; and seacocks are most likely to seize precisely on the day you need them, because they have not been operated for years.
A valve you never operate is a valve that will not work on the day it matters.
A simple but vital routine
Operate it once a month:fully close and open each valve so it stays free; a valve left in the same position for too long will scale up.
Keep a bung to hand:hang a correctly sized tapered wooden bung next to each valve; if the seacock fails one day, your back-up plan is already in place.
Corrosion in the yard:on the hull side, check for pink discolouration (dezincification), especially where unsuitable materials have been used.
A valve is only as sound as the hose connected to it; double hose clips should be standard. Below-waterline toilets and intakes are among the riskiest systems if a valve is left open.