Association Forum - After the thru hull then what [?]

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

After the thru hull then what [?]

New Topic

Topic Locked

Printer Friendly

Author

Topic

tmhansen
Captain

Member Avatar

USA
397 Posts

Initially Posted - 04/09/2003 : 15:44:23

My boat is already equipt with bronze through hulls but after that I have two gate valves, one plastic. I want to replace them with ball valves but I am unclear on whether I can just install a ball valve or if I should install a flanged seacock. What is the difference, other than the flange? When is each used?

Todd Hansen
Fior Gra'
San Luis Obispo, CA

Edited by - on

jm
Captain

Members Avatar

Canada
290 Posts

Response Posted - 04/09/2003 : 15:53:27

<snip> from http://www.boatus.com/seaworthy/swmbs.asp

Defining a proper seacock..

All thru-hulls below or near the waterline must have a valve that can be closed in an emergency or when the boat will be left unattended for more than a few days. Traditional bronze seacocks are acceptable, but gate valves and many plastic thru-hulls should not be used at thru-hulls below the waterline.

Gate valves have internal parts that deteriorate and snap off. And unlike a seacock, which has a handle that is clearly open or closed ("positive action"), a gate valve's wheel may or may not be closed. Even turning the wheel will not confirm that the valve is closed. The internal mechanism could have become jammed open by debris, for example, but feel as though it had been closed.

Plastic seacocks are brittle and can be easily broken by an errant foot or a stowed anchor. The exception is Marelon thru-hulls, which are made of glass-reinforced plastic and are acceptable for thru-hull installations below the waterline. Marelon seacocks have been tested (most sizes) and approved by Underwriters Laboratories. While probably not as prone to mechanical freezing as their bronze counterparts, Marelon seacocks must also be taken apart, inspected, and lubricated periodically.

Finally, some boat builders have recently been installing ball-type bronze seacocks that use a Teflon-coated ball (either plastic or stainless steel) instead of traditional tapered drums. These newer valves are acceptable, especially if they have a flanged base and are mounted on a backing block. The ball valves are not inclined to mechanical freezing, but the models that can be taken apart (some can't) should be inspected occasionally to make sure they haven't become clogged by debris.

Edited by - jm on 04/09/2003 15:54:19

Edited by - on

Arlyn Stewart
Master Marine Consultant

Members Avatar

USA
2984 Posts

Response Posted - 04/09/2003 : 19:54:52

I think it depends on where the seacock is. Knowing that a non flanged valve places all the stress on the thin layer at the thread depth is not comforting. So, if the valve is subject to "any" impact... it should be a flanged valve.

Flanged valves differ from unflanged in that the have straight threads instead of tapered pipe threads. This means that they can and should be screwed fully untill the flange of the valve draws against the backing block and in the process... holds the thru hull to the hull. Then... short screws secure the valve to the backing block which is bedded in so as to avoid turning.

btw...when drilling the holes for these screws... use a spacer on the drill bit to prevent it from going deeper than intended <img src=icon_smile_sad.gif border=0 align=middle> No, I haven't...but I'm betting its been done. Along this vein, a few years ago on this forum or the Trailer Sailor... someone asked if the screws going thru the hull to hold the seacock on...should be round head or counter sunk flat heads. <img src=icon_smile_shock.gif border=0 align=middle> Of course... the screws don't go thru the hull. <img src=icon_smile_approve.gif border=0 align=middle> And, I tell that certainly not to embarrass the poster... but just two years ago... while hauling my boat to Michigan for a summer cruise, I stopped at a rest stop and parked next to a gentleman also pulling his rather large fin keeled boat. I couldn't help but notice the thru hull... with three screw heads visible.

Arlyn C-250 W/B #224
<img src="http://www.stewartfam.net/arlyn/rr.jpg" border=0>
N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

Edited by - on

Leon Sisson
Master Marine Consultant

Members Avatar

USA
1893 Posts

Response Posted - 04/10/2003 : 00:21:34

Todd,

I heartily agree with what jm/BoatUS and Arlyn have said about seacocks and through-hulls. Although, I'd say it's OK for the seacock flange mounting screws to be installed all the way through the hull. In Boatowner's Mechanical and Electrical Manual second edition by Nigel Calder on page 385 there are two drawings of seacock installations with the flange bolts going through the hull. One is captioned "Proper seacock installation in a wood or fiberglass hull". I think either method (Arlyn's or Nigel Calder's) would work OK.

By the way, on that same page there's a drawing captioned "How not to install a through-hull or seacock!" which still looks stronger than the stock Catalina "to-hull".

In answer to "... can just install a ball valve or if I should install a flanged seacock?" Again from Nigel Calder, page 384: <BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>The ABYC requires that any through-hull below the waterline (both static and heeled) be fitted with a seacock (except self-draining cockpits that discharge above the static waterline), that the seacock be manufactured from corrosion-resistant materials (which excludes brass gate valves and globe valves), that it be able to withstand a 500-pound weight applied at its inboard end in any direction, for 30 seconds, and that its handle be easy to operate.
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>That whole four page section on seacocks in Boatowner's Mechanical and Electrical Manual is rather strongly worded and unambiguous. As I recall, insurance statistics indicate that failed underwater fittings are the number one cause of unattended boats sinking, exceeding all other causes combined. When replacing my original "to-hulls", I went by the book and didn't try to cut corners.

-- Leon Sisson

Edited by - on

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.