On Thu, 21 Apr 2005 14:26:51 -0400, DSK wrote:

All were "big nut" thru-hulls with gate valves. I replaced them with
brass NPT ball valves, which I service yearly and I have double SS
clamps everywhere. No problems whatsoever. If I were in salt water, I
would act differently.


Why? Do boats not sink in fresh water or something

Sure they do, but sal****er eventually dissolves brass fittings,
meaning they are a no-no in even brackish water.. "Proper" seacocks
are salt-resistant bronze, or these days, Marelon. In fresh water, you
can use brass plumbing ball valves...at about 1/4-1/8 the price of
bronze. The actual thru-hulls are still bronze: it's the cocks screwed
onto them that are brass, with teflon tape and thread sealer between.




The issue is less of gate valve vs ball valve, than it is NPT vs flange
and one of corrosion. Nowadays common cheapo hardware store grade valves
are far more corrosion resistant than anything from years ago (except
possibly the super-expensive Monel sea cocks, which I've seen exactly
once in a lifetime).

A sea cock should (in theory) be supported by a flange, not just screwed
onto a protruding pipe. There are lots of ways... including just plain
heeling... that the pipe & valve come under strain. Still, with modern
materials and good attention to detail (btw it is possible to
overtighten NPT connections & split the casting or collapse the pipe
wall) it should be just fine.

I have been careful with the hoses and whatnot to avoid lateral
forces. I suppose if the engine came loose and slammed into the ball
valve at speed, I'd be in trouble, but that could easily tear a hole
in the actual hull, meaning I have bigger issues.

R.