is this the law?

[Dave Hussey]

I was told by the salesman in the local boat candy store that I would have to use seacocks that have integral base flanges and bolt to the hull in new installations. He said it was a requirement that they be able to withstand 500 lbs of side force. Is he just trying to improve his bottom line and lighten my wallet????

 

[NateHanson]

I'm Shocked! :eek: I've never heard such prudent advice from a boat store salesperson before! Just kidding (mostly).

Actually he's absolutely correct. It's not "law" per say, but it is the ABYA guideline, and more importantly it's good practice. You should only use proper "seacocks" for below the waterline thru-hull installations. Ball valves that just screw on the end of the thru-hull are unsupported, and actually even have incompatible threads (tapered rather than straight) so they won't engage the thruhull for more than a couple threads. Bad idea.

For a good video lesson on the subject go to ZMIseminars.com. Zimmerman Marine is a boatyard where Steve D'antonio works, and he's a frequent contributor to Ocean Navigator, on subjects of boat maintenance. He made a dozen or so short video seminars on different subjects, and thruhulls is one of them.

 

[Loren Beach]

Valve Talkin'

No "law" since that implies gov't presence...
More like what I would call "best practice."

Here are a couple of threads on this site, each with pictures of flanged seacocks.
http://www.ericsonyachts.org/infoexchange/showthread.php?t=2992&referrerid=28

http://www.ericsonyachts.org/infoexchange/showthread.php?t=1138&referrerid=28

There are other equally excellent threads, and a bit of searching with words like Sea Cock or Thru Hull or similar wording will give you a lot of good reading. Note that any thread can be printed without headers & footers by first sellecting "Show Printable Version" under Thread Tools.
Any photos you fancy can be clicked-and-dragged to your desktop, as well.

I have heard a surveyor friend refer to a thru-hull being able to pass the "kick test" and this mental image seems to clarify it for my old gray cells.


Cheers,
Loren

ps: regarding the effect on your wallet, the cost of the valve will be minor conpared to the haul-out cost to install 'em, and microscopic compared to the cost of interior restoration after a major flooding incident...

 

[Dave Hussey]

Interesting stuff! Thanks. I see the good sense of it, especially when you consider that the thickness of the metal between the threads of the thruhull nipple is, what, 1/16th of an inch? (at best) ... not a lot of comfort there.
But I did read somewhere that a marine grade seacock has 'bolt' threads on the bottom and 'pipe threads' on the top...I can't remember the source of this info though.
Dave H

 

[NateHanson]

But I did read somewhere that a marine grade seacock has 'bolt' threads on the bottom and 'pipe threads' on the top...I can't remember the source of this info though.
Dave H

Only special "combination thread" thru-hulls have NST (straight thread) and NPT (pipe thread) on the base and end of the thru-hull respectively. These are made to be attached to ball valves, and will engage more threads than a ball-valve to straight thru-hull connection.

Standard thru-hulls, and the ones you'll find on the shelf at your local chandlery are straight threads all the way down (like a bolt).