Sea Cocks -- PTFE Tape vs Caulk and Oakum

[daveNZ]

From the Trudesign web site........
"QUESTION
What sealant should I use between a bronze or stainless skin fitting and a TruDesign ball valve ?
ANSWER
The same options as you would use for sealing any TruDesign composite fitting to a TruDesign composite Ball Valve: #3M 5200 #3M 5200 FT (Fastcure) # Sikaflex 291i # Loctite 55 Pipe Sealing ..."

[NYSail]

Groco says a couple wraps of wide tape then a fair amount of quality pipe dope on both pieces. With too much tape you will restrict the depth in which you can match the parts together..... unless you have to have the final position different than fully tight.

[Dockhead]

Originally Posted by Cowpoos

I don't really want to play the devil's advocate here, but that metal your new seacocks are made of looks like Brass and not bronze?? If brass it has a much higher zinc content which will make your seacocks an anode to a point.

Very happy to be corrected in this case.

Those are Maestrini 85-5-5-5 bronze fittings as originally specified by Moody. These are the best European underwater fittings made of the best grade of bronze for this purpose.


I am now replacing the last batch of them; the first 8 I replaced two years ago. These last ones are now 19 years old and are actually still in seaworthy condition, just that one of them is getting hard to close, and the handles are starting to rust. I could have probably saved the €1500 all this stuff cost me but it was time to take them all apart anyway for a thorough inspection, and once you do that, you might as well renew them.


It's beautiful hardware; a shame actually that they will be out of sight. They have been somewhat improved over the last decades; Maestrini now provides stainless handles. They are expensive but worth every penny in my opinion.








Maestrini s.r.l.




I have NOT replaced the through hulls, and that on the advice of my surveyor in Cowes. I have file tested every one of them for dezincification; they are perfect. My surveyor says their life is basically unlimited provided they are not exposed to stray currents.

[Dockhead]

Originally Posted by chris95040

. . . I don’t know if your seacock threads are tapered pipe threads or not. If not, I think you need some sort of thread sealant.

NPT and NPS fittings are unknown in Europe; here everything is BSP, which has tapered threads. BSP threaded joints are inherently watertight, so maybe PFTE tape is appropriate? But Moody used oakum and caulk. Their choice of caulk, whatever it was, was good -- because I didn't have any trouble getting the fittings apart even after 19 years I would like to leave a similar legacy for whoever owns my boat 19 years from now.

[s/v Jedi]

Originally Posted by Dockhead

NPT and NPS fittings are unknown in Europe; here everything is BSP, which has tapered threads.

No, BSP has both tapered and linear variants just like NPT and NPS. Pretty sure the skin fitting has linear thread so hope your valves have that too.
https://en.wikipedia.org/wiki/British_Standard_Pipe

[Wotname]

Originally Posted by Dockhead

NPT and NPS fittings are unknown in Europe; here everything is BSP, which has tapered threads. BSP threaded joints are inherently watertight, so maybe PFTE tape is appropriate? But Moody used oakum and caulk. Their choice of caulk, whatever it was, was good -- because I didn't have any trouble getting the fittings apart even after 19 years I would like to leave a similar legacy for whoever owns my boat 19 years from now.

A minor correction - BSP has two thread forms, parallel and tapered.

For a jointed connection, the male will be BSPT and the female can be either BSPT or BSPP. In Oz (and the UK??), the female will be BSPP.

See more here https://en.wikipedia.org/wiki/British_Standard_Pipe

[Dockhead]

Originally Posted by Emmalina

Hemp and paste is my sealant on everything. You can even make adjustments as it expands over time. Teflon is ok on small stuff .

That's what Moody used. What kind of paste?

[s/v Jedi]

Originally Posted by Wotname

A minor correction - BSP has two thread forms, parallel and tapered.

For a jointed connection, the male will be BSPT and the female can be either BSPT or BSPP. In Oz (and the UK??), the female will be BSPP.

See more here https://en.wikipedia.org/wiki/British_Standard_Pipe

So the male thread of a skin fitting is parallel, right? I called it linear but that’s just a different word for the same thing. I can’t imagine skin fittings that don’t allow to be cut to size.

[Dockhead]

Originally Posted by s/v Jedi

So the male thread of a skin fitting is parallel, right? I called it linear but that’s just a different word for the same thing. I can’t imagine skin fittings that don’t allow to be cut to size.

No, tapered. It's the female BSP thread in some European countries which is straight. Edit: That was wrong. They are ISO 228, which is BSPP or straight threads, on both male and female.

You can of course cut skin fittings to the required length -- they would be useless otherwise. One reason I haven't changed mine is the massive PITA to cut them properly, debur them, chase the threads, etc. It should be done in a machine shop.

More info: https://en.wikipedia.org/wiki/British_Standard_Pipe. More or less the whole world uses BSP pipe thread standards except the U.S. and Canada.