[Public-List] seacocks

[J Bergquist]

There is a really great article about seacocks in the current issue of
Professional Boatbuilder magazine. You can find a digital copy of the
magazine (for free!) at:

http://www.proboat-digital.com/proboat/20080809/

I thought I knew something about seacocks. What I learned by reading
this article is that all of the seacocks in my boat are improper,
which made me think 2 things:

1. I should probably change them before too long.

2. They have lasted a long time as is. So maybe it's not the first
thing that I should do, and it does seem like it would be quite a job.

I am sure many folks reading this list already know the proper seacock
installation ABYC specification, but it was news to me so I assume
there are others out there who also didn't realize it. Basically, what
I learned is that bronze thru-hulls have straight NPS (not NPT)
threads on them, which means if you screw a standard ball valve (which
normally has NPT threads), only a few threads will register before you
hit the taper. In reality, thru hulls are supposed to be screwed into
a seacock that has matching NPS threads from the outside. The seacock
gets pre-installed with lag screws so that it is fixed and you use a
special wrench to turn the thru-hull into the seacock itself from
outside the boat. This process is illustrated and explained in the
article.

Anyway, what I have is standard ball valves with NPT threads screwed
onto the ends of my thru-hulls. This is basically exactly wrong. I had
no idea. Apparently it is a common mistake made by do-it-yourselfers
and even some professionals. I thought my installations were correct
because they were ball valves instead of gate valves. But the proper
ABYC-compliant installation should have actual seacocks lag screwed to
the backing block and with the thru hull threaded all the way in from
the outside.

I just thought there might be other folks out there who would find
this article interesting.

There is also a sweet article about fiber orientation and lamination
defects which is pretty cool.

Later,

J Bergquist