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.

Why not just do it the right way? NPS thruhull to NPS valve.

Doug

"Roger Long" wrote in message
...
Calder and other authorities are dead set against putting NPT ball valves
on NPS through hull fittings as is often done when replacing gate valves.
The geometry of the thread engagement gives me the willies as well because
all the load is on just one or two threads due to the taper.

My boatyard tells me that they do it all the time however as does everyone
else. The gate valves on my 1980 boat haven't broken off yet either. I
just threaded a one half inch ball valve and through hull together and it
doesn't look or feel as bad as the theory.

Except for a couple of above waterline drains, the seacocks I'm going to
put in will be flanged and bolted. I'm just curious though, has anyone
ever heard of a NPT valve on a NPS through hull breaking off or leaking?

--

Roger Long

Is a"gate valve" the same as the outdoor faucet on most homes? If so
what is the problem with them?

Allen

Doug Dotson wrote:

Why not just do it the right way? NPS thruhull to NPS valve.

Doug

"Roger Long" wrote in message
...

Calder and other authorities are dead set against putting NPT ball valves
on NPS through hull fittings as is often done when replacing gate valves.
The geometry of the thread engagement gives me the willies as well because
all the load is on just one or two threads due to the taper.

My boatyard tells me that they do it all the time however as does everyone
else. The gate valves on my 1980 boat haven't broken off yet either. I
just threaded a one half inch ball valve and through hull together and it
doesn't look or feel as bad as the theory.

Except for a couple of above waterline drains, the seacocks I'm going to
put in will be flanged and bolted. I'm just curious though, has anyone
ever heard of a NPT valve on a NPS through hull breaking off or leaking?

--

Roger Long

"Allen McCann" wrote in message
...
Is a"gate valve" the same as the outdoor faucet on most homes? If so what
is the problem with them?

Allen

Doug Dotson wrote:

Why not just do it the right way? NPS thruhull to NPS valve.

Doug

"Roger Long" wrote in message
...

Calder and other authorities are dead set against putting NPT ball valves
on NPS through hull fittings as is often done when replacing gate valves.
The geometry of the thread engagement gives me the willies as well
because all the load is on just one or two threads due to the taper.

My boatyard tells me that they do it all the time however as does
everyone else. The gate valves on my 1980 boat haven't broken off yet
either. I just threaded a one half inch ball valve and through hull
together and it doesn't look or feel as bad as the theory.

Except for a couple of above waterline drains, the seacocks I'm going to
put in will be flanged and bolted. I'm just curious though, has anyone
ever heard of a NPT valve on a NPS through hull breaking off or leaking?

--

Roger Long


Answer is yes. You turn the round handle and this screws down a gate across
the diameter of the pipe, sort of like a guillotine.

There are several potential problems with them and I'll just mention a
couple:

-not really intended for marine use so you don't know the type of alloy used
-the attachment to the hull is a weak point and they can be broken off
-you cannot easily tell if the valve is open or closed by looking at it
-they tend to seize up if you don't exercise them frequently and people
don't tend to do this because it is a pain to turn the valve a dozen time to
close/open it

Lots of older boats have them. If you maintain them you can live with them
but lots of folks replace them with proper seacocks.

I've never known my outdoor faucet to be in sal****er all the time.
Also, the failure of your outdoor faucet will not likely sink your
house.

My boat had gate valves when I bought it. They were common
practice back when my boat was made. No longer. The surveyor
required that I replace them all.

Doug
s/v CAllista

"Allen McCann" wrote in message
...
Is a"gate valve" the same as the outdoor faucet on most homes? If so what
is the problem with them?

Allen

Doug Dotson wrote:

Why not just do it the right way? NPS thruhull to NPS valve.

Doug

"Roger Long" wrote in message
...

Calder and other authorities are dead set against putting NPT ball valves
on NPS through hull fittings as is often done when replacing gate valves.
The geometry of the thread engagement gives me the willies as well
because all the load is on just one or two threads due to the taper.

My boatyard tells me that they do it all the time however as does
everyone else. The gate valves on my 1980 boat haven't broken off yet
either. I just threaded a one half inch ball valve and through hull
together and it doesn't look or feel as bad as the theory.

Except for a couple of above waterline drains, the seacocks I'm going to
put in will be flanged and bolted. I'm just curious though, has anyone
ever heard of a NPT valve on a NPS through hull breaking off or leaking?

--

Roger Long