Quick answers needed on Seacocks

[Doug]

I've read all the archives and one question has not been asked or answered regarding seacocks/ball valves/thru-hulls.Here is where I need help before friday's haul-out:1) Bronze thru-hulls have straight (nps) threads, not standard plumbing tapered threads (npt).2) Seacocks (real ones with a boltable flange) have straight thread (nps) on bottom and tapered on top to accept tailpipes that also have a tapered thread that jams when tightened (3-5 turns) to create a seal.3) Bronze ball valves have NPT (tapered) threads on both ends. I have read response after response and have even talked to Hunter (parts dept) to find that most people are using cheaper ball valves (albeit bronze and marine grade) for connection to the thru-hull. This means screwing a tapered threaded valve onto a straight threaded thru-hull. Not only is this not a leakproof and correct connection but it is weak. It's like jamming a metric or british thread onto our standard threads. It just ain't right.What's the deal? We are going to replace all thru-hulls and valves/seacocks this weekend and I would really like to know the real story on this stuff if anybody knows for sure.Thanks.Doug

 

[Bill]

Threads

You are correct about the straight -vs-tapered but most people have used both. The locking nut on the thru hull takes most of the stress of holding the thru hull in place. I think you will find that the gate valves they are replacing have the same threads as the ballcock and I have not read where this has been a proven weakness but rather the design of the gate valve itself is the problem, i.e. not knowing if the valve is open or closed etc. I have used the ball valves and have gotten them tightened to the point where they will not fall off or vibrate loose. I did however file down several threads on the thru hull and created a taper. You can even use lifecaulk on the treads if you even further worried about the valve leaking. In MY Opinion, and that is just what it is, I have no certifications in this area, the ball valves can be used but if you really need more piece of mind then buy the seacock. I know many will disagree with me but that will not be the first time. DO make sure you use bronze and not brass.

 

[Ed Schenck]

Love those ball-valves.

What an inexpensive and confidence inspiring upgrade! And you and Bill are absolutely correct about the thread issues. Despite having replaced three gate valves with ball valves and having no leaks I will replace ALL with real seacocks before I leave Lake Erie. Just something about having that big bronze shut-off snugged right down against the hull(see link).My H37C originally had an elbow on the thru-hulls with the gate valves screwed on to the elbow. This was even worse since there are so few threads on the elbow to thru-hull connection. The ball valves were threaded directly on to the thru-hulls.

 

[howard meyer]

marelyon

we replaced ours with marelyon ball valves.. the thread matches and there are no dissimilar metal problems, no corrosion either.

 

[Sam Lust]

The quick answer is "Don't worry about it"

Regardless of whether the thread is straight or tapered pipe, there is enough interference in the thread mating to provide a seal forever. Aside from that, any through hull/sea cock combination should be put together with Teflon tape.For the record, The thread on the base of a Forespar, "RC" Marelon sea cock IS tapered pipe. The proper method of installation to the straight thread through hull according to Forespar is to adjust (cut) the length of the threaded portion of the through hull so the thread interference tightens up as the base flange socks down in contact with the hull backing plate.