Seacock

The critical isolation valve.

The seacock is the isolation valve that allows any below-waterline penetration to be closed in an emergency. ABYC standard H-27 requires a proper seacock — not a simple threaded ball valve — for any opening below the vessel's maximum heeled waterline. A seacock is a flanged, full-bore valve designed to withstand accidental impact without failure; a threaded ball valve is not.

The seacock assembly threads onto the male spigot of the skin fitting inboard of the backing nut. Material must be compatible with the skin fitting to avoid galvanic corrosion. A complete seacock assembly comprises the following components:

• Seacock body

  Bronze or Marelon valve body housing the ball mechanism, threaded onto the hull fitting and secured against rotation.

• Ball valve

  Ported ball providing full-bore open and fully closed positions with a quarter-turn of the lever.

• Lever handle

  Operating lever showing open/closed orientation at a glance; removable on some designs as a security measure.

• Valve seats

  PTFE or elastomer seats providing a watertight seal against the ball in the closed position.

• Stem packing

  PTFE or graphite packing sealing the valve stem where it exits the body.

• Gland / packing nut

  Threaded nut compressing the stem packing to prevent leakage around the valve spindle.

All seacock handles should be exercised — fully opened and closed — at minimum monthly intervals to prevent seizure from corrosion or marine growth. A seized seacock that cannot be closed in an emergency is as dangerous as no seacock at all.