Sea Cock sizes,what size should we be using?

As a follow on to my posting on June 15th 2009 I was wondering about how to size a boats engine sea cock?

Here is a wide selection of solid bronze sea cocks,wonderfull items to have and hold,we trust them with our boats,so our lives,so please buy the best and service them on a regular basis.

I can not remember ever reading about sea cock sizing to a boats engine,in the past I have normally used a 38mm size but what size is needed,I asked Dudley Dix, at  http://www.dixdesign.com/ below is his reply..

I have always sized the seacock to the intake size of the cooling water pipe of the motor. I have the cooling water seacock from "Tai-Neam" on my desk and that is 20mm. That is the same as "Black Cat" but both motors were Yanmar 18-20hp. I would expect yours to be about 25mm but your owner's manual should tell you the pipe size. The Perkins drawings on data sheets are very sketchy, with minimal info. The Yanmar sheets show all pipe sizes. The 80hp 4JH range only has a 26mm inlet, so yours is unlikely to be more.

Regards,
DD

Thanks for this info,

Roy