What do the ABYC definitions mean?
27.4.4 Seacock - A type of valve used to control intake or discharge of water through the hull. It is operated by a lever type handle usually operating through a 90° arc, giving a clear indication of whether it is open or shut, and is typically of the two following types:
18.104.22.168 Flanged Sea Valve – A Seacock with an integral flange used to individually and securely mount the device directly to the boat hull structure.
22.214.171.124 In Line Ball Valve – A Seacock designed to be supported entirely by the through-hull fitting.
Some key points of ABYC H-27:
27.5.1 All piping, tubing, or hose lines penetrating the hull below the maximum heeled waterline, shall be equipped with a seacock to stop the admission of water in the event of failure of pipes, tubing, or hose.
27.5.4 Seacocks shall be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull Fittings and Sea-Valves.
27.5.5 Thru-hull fittings shall be designed and constructed to meet ANSI/UL 1121, Marine Through-Hull Fittings and Sea-Valves.
27.6.1 A seacock shall be securely mounted so that the assembly will withstand a 500 pound (227 Kg) static force applied for 30 seconds to the inboard end of the assembly, without the assembly failing to stop the ingress of water.
126.96.36.199 The installation shall prevent any movement of the assembly.
188.8.131.52 Threads used in seacock installations shall be compatible (eg. NPT to NPT, NPS to NPS).
The above comes from ABYC H-27