what is a proper seacock?

[monkeymikey2000]

When I bought my boat (first boat with thru-hulls below the waterline) I replaced the ancient looking seacocks when I had the boat hauled. I replaced the actual thru-hull mushrooms with new bronze ones, they are held in with the nut that comes with them, then I got the new bronze ball valves and simply screwed them on the 3 inches of remaining thru-hull with some sealant just like the old ones. That was 6 months ago and no leaks or troubles since. Someone just told me that I did it wrong and the proper way is to buy a flanged ball valve (twice the price!) and drill more holes in the boat, bolt this ball valve to the hull then screw the mushroom into the ball valve from the outside which also requires cutting the mushroom shorter if it is to long. I decided to walk through the boatyard and see what other boaters had done and I didn't see one boat with a flanged, bolted down seacock. I can see how it would be stronger but I think it is a overkill and if one replaces the mushrooms and ball valves every few years there should be no concern. anyone else have any thoughts on this?

[bcooke]

A lot of people get by with ball valves screwed onto through hulls but when it comes to holes below the waterline I opt for the maximum amount of security that comes with a proper seacock.

Not only does the wide, flanged base of a seacock spread a side load much better but a ball valve uses pipe (tapered) threads so the actual thread engagement is really quite limited. Seacocks are straight threaded so the entire length of the threaded portion is carrying the load.

I believe ABYC standards rule out using thru-hulls with ball valves below the waterline and insurance companies like the ABYC standards. That might or might not be something for you to consider.

Ball valves are cheaper but I feel the added security is priceless. In the big scheme of things the added cost is but a small fraction of my annual maintenance cost anyway.

Just my 2 cents.

-Britton

[Tim]

In the most basic terms, a proper "seacock" is a valve with a bolted-on flange for additional support. Many (most) seacocks use ball valves inside, but the flange provides substantial support to the valve. Older type seacocks used a tapered plug inside, which was (and is) a good design but requires maintenance in order to remain leak-free. Spartan Marine still makes traditional tapered plug seacocks.

The threads on a standard straight ball valve are a different type than those on most through hulls, so the valve cannot screw down to the end of the threads--further weakening the installation.

There's nothing wrong with a flanged ball valve (aka seacock). Apollo, Conbraco, Groco, and Perko all make acceptable flanged ball valves, and these meet or exceed the standards of ABYC. But I'd recommend against using inline ball valves screwed onto an existing through hull fitting--it's just a poor installation practice, and most surveyors would make a note of these installations and recommend changing to a flanged, through-bolted installation.

[Ceasar Choppy]

I believe the ABYC requirement is that the seacock must be able to withstand 500 lbs of side pressure for at least 30 secs. i.e. the boat gets hit with rough seas and things start shifting or flying around, hitting the seacock and possibly shearing it off.

Screwing an in-line ball valve to a through-hull without flange support would probably not stand up to that kind of load.

Just finished replacing 8 of them on my boat!

[dmairspotter]

Question on seacock installation. I just replaced a bunch of junk valves on my boat. I used bronze through huls with marelon seacocks. I glassed in thick marine ply blocks inside the hull, installed the through hulls by screwing down the seacocks till all was snug (with proper bedding compound of cource). Lastly, I used screws to fasten the seacocks to the plywood backing plate. This eliminated three hull penetrations per through hull. I know it doesnt give the same support as through bolts, but it seemed a whole lot better than ball valves (or seacocks with no auxiliary srcewing or bolting, which I have seen on some boats). Any thoughts?

[bcooke]

Well, I know that Forespar does not recomend mixing bronze hardware with their Marelon products but I don't know why.

As for screws over bolts. It is all a step towards the right direction but I wouldn't be afraid of adding bolt holes through the hull. When I first installed seacocks on my boat I was rather tentative about adding any more holes in the hull than was absolutely necessary. Now, with some experience behind me I feel a lot less afraid about them. Properly bedded bolts will never leak. If they do then take them out and bed them properly. You can always bed with 5200 and then the bolt holes will be drier than the fiberglass hull ever will. Better yet, bed the bolts with 5200 the first time and the bolts will break before a drop of water comes in.

-Britton

[monkeymikey2000]

Yeah, that is a good idea with the screws, I never thought of that. If you do put the bolts right through the hull, what kind of bolts are you susposed to use, counter sunk bolts? This way you would have a nice smooth finish, or at least carriage bolts maybe. I don't know, how far one must go to satisfy themselves that there boat is perfectly safe and never going to sink? I think we all get a little paranoid sometimes, I know some skippers who will never set foot on a boat with a gasoline engine because of all the mights and what ifs. anyway, just my 1 cent.
Mike

[Tim]

Screws into a beefy backing plate is a decent way of securing a flanged seacock in place for a boat used in typical coastal conditions, and does avoid the need for the extra holes in the hull. In virtually all conditions, this will work just as well as the bolts, but of course will not be ultimately as strong.

Assuming the fiberglass skin is thick enough, countersunk bugle head bolts (technically machine screws) are a good choice for bolting the seacocks in place. Countersink the head just flush with the hull. On some solid fiberglass boats, though, the skin may not be thick enough to allow for a proper countersink; in this case, carriage bolts or hex head bolts should be used, which of course protrude from the hull and are not as sleek. If using bronze seacocks, the fasteners should be silicon bronze; for Marelon, either bronze or stainless could be used.

In an ideal world, there should be a heavy reinforced solid pad on cored boats, or thinner-skinned solid hulls, so that flush through bolts could be used. This is rarely the case, however, so one must adapt as necessary. Using screws into an internal backing pad is an acceptable way to get around this issue, and is most defintely stronger than ball valves.

There are differences in the expansion/contraction rates of bronze and Marelon that preclude their use together in the same application. Be very wary of doing this--one should stick with all of one material or the other for each individual location.

Note that many new production manufacturers use ball valves or other similar installations for their underwater through hulls. The ONLY reason they do this is to save $$$ on the bottom line, meaning lower prices for the customer and higher profits for the manufacturer. It takes a lot of labor and elapsed time to properly install the reinforcements for through-bolted seacocks, and to install the fittings themselves. This is why you only see such installations on the higher-end boats (with a correspondingly higher price tag).

There's a reason that Hinckley, Morris, Swan and others cost so much more than Catalinas and Beneteaus--it's all about the labor required to make careful installations of all the various components and systems.

[Figment]

Well, I know that Forespar does not recomend mixing bronze hardware with their Marelon products but I don't know why.

Last night, flipping through an issue of GOB, a Forespar ad caught my eye that showed a bronze thru-hull threaded into a marelon valve. Sure enough, the text of the ad reads "can be used in combination with metal fittings" (paraphrased).

hmph.

[Tim]

Hmm. Interesting change of direction there.

I guess we have to go with what the manufacturer says. But I bet they changed their official stance because so many people were otherwise choosing to stick with bronze, in fear of mixing the two materials.

[bcooke]

But I bet they changed their official stance because so many people were otherwise choosing to stick with bronze, in fear of mixing the two materials.

I wasn't sure if I should ask the question but why not use a Marelon thru-hull with the Marelon seacock? They are just as readily available and prices are about the same as I remember.

-Britton

[dmairspotter]

My thinking was thus:

Metal (bronze) for the thruhull because it's strong(er) than Marelon, more abrasion and rough handling resistant.

Mate that to a Marelon seacock because the marelon won't corrode, either to itself or to the thru hull. 10 years from now it should be easier to remove/rebuild/replace if need be.

That was my reasoning anyway. It was distinctly colored by the experience of removing 30 year old valves and seacocks from the boat. I used everything up to C4 and I was considering packing the bilge with that and sending the whole thin into orbit!

[keelbolts]

There are valves and there are seacocks. Where a seacock is indicated, nothing else will do. If you can't afford a proper seacock, you can't afford a boat. A bronze seacock, if dissassembled, cleaned, and greased yearly will outlive you if you are in diapers. I replaced the bolts, but the seacocks in my boat are original which makes 'em over 50 years old. I worry about many things on my old boat, but the seacocks aren't on the list. In any case, you should have a wooden plug tied to each of your thru-hulls just in case...

[Steve Laume]

I had to remove some through hull fittings on a boat that had been installed with 5200. It proved to be very easy because they were bronze. All I had to do was heat them untill the 5200 got soft and they pulled right out. If theyhad been plastic I think the through hulls would have melted before they came lose. Just another reason to stick with traditional materials, Steve.