On Tue, 19 Apr 2005 18:07:35 -0400, Larry Bradley
wrote:

I just went through this operation. I have a 35 year old sailboat that
does not use the proper bolted-through through-hulls, just the kind
with a big nut on them. The have then been glassed in. There were gate
valves on all of them.

This year, having the engine out, I thought I would try replacing a
few that were in formerly "impossible to get a pipe wrench on" places
when the engine was in.

I tried two - the engine water intake and a cockpit drain. I removed
the gate valve, and got ball valves from Home Depot (I sail in fresh
water, have used them before with no problems). These thread onto the
through-hulls quite nicely - way down the thread, not just at the end.
Lots of pipe dope. No way these will come off - there is a lot of
thread.

I've no way of knowing if the ball valves are NPT or NPS - they don't
say - but I would assume NPT, since damn near everything else in the
plumbing department is NPT.

I replace a 1" gate valve and a 1/2" gate valve this way.

Now that I think about it, several years aho I replaced the gate valve
on the head intake with a ball valve, and it works fine.

YMMV

I've done the same thing in the galley, head, and both cockpit drains.
Only the freshwater intake for the engine is a "proper" seacock. The
only thruhull I replaced was the freshwater intake in the head.

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.

I do not disdain the arguments, but like you, I have confidence that
these buggers are NOT coming off and are much safer than the original
gate valves. Also I have plugs tied to each thru hull, which I don't
see a lot of here on Lake Ontario, even though that is a "standard
precaution" as well.

R.