Seacocks are a crucial component of any well designed boat plumbing, engine cooling or water ballast system. Seacocks can be used to control the inflow or outflow of water and should be considered mandatory for all below-the-waterline connections. Seacocks may be constructed using a ball valve but NOT all ball valves are seacocks.
A true seacock features a flange that is bolted (or screwed) to a fairing block afixed to the hull. Top quality seacocks are manufactured by Groco, Buck Algonquin and Perko in marine grade bronze. Forespar manufactures seacocks in Marelon that is a formulation of glass-reinforced Dupont Zytel. All are ABYC compliant for marine use.
Most seacocks feature NPS (straight) threads on the flange (hull) side with NPT (tapered) pipe threads on the top side. Marelon seacocks feature NPS (straight) threads on both sides. Forespar offers Marelon hose fittings with NPS (straight) threads that are designed to work with their seacocks.
Ball Valves operate with a quarter turn similar to a seacock, but are not designed to be attached directly to a thru-hull fitting. Most ball valves feature NPT (tapered) threads on both ends and are compatible only with tapered pipe fittings.
Ball valves are suitable for liquid control applications within the boat hull. Ball valves are superior in function to old-fashioned gate valves. Ball valves offer rapid action and provide positive visual feedback whether open or closed.