Thru-hulls and seacocks on a E38....

[NateHanson]

Marelon is glass-reinforced nylon. I'd expect the piece you bought is a similar glass-reinforced product, just not the forespar proprietary material "marelon".

If I recall correctly, you can use 4200 on marelon. I think it is polysulfide that's not safe for plastics.

Nate

 

[Loren Beach]

"Plastics!" (as Ben was told in that movie)

Michelle,
There are many plastic compounds, some fiber-reinforced and many not, that are used for marine/RV piping and fittings.
Nylon is strong, but is not (AFAIK) specified for use below the waterline. Another above-WL material is acetate.
Marelon (r) is a reinforced composite plastic material suitable for below the WL. It first appeared in this country in the late 70's, if I remember right, as an import from RC Marine, down under in Australia. Then Forespar bought them and put it under thier name and seems to have continued development on it.
As to transducers, they seem to have gone to "plastics" for quite some time now. I can remember when the threaded barrel was bronze and the innards were some sort of plastic, with the wires emerging from a hard "potted" material at the top. Personally I would be happy with whatever material the instrument builder was specifying and providing. For instance, my Raymarine instruments came with black "plastic" thruhulls and I have no reason to doubt that they will last until these instruments get replaced in another 15 years -- and I probably will have died or bought a trawler by then.
Speaking of instrument transducers, I note that the plastic ones used by several instrument builders are all from one common supplier, "Airmar."

As to sealant, just check the specs on the package. There are some, like LifeCaulk(r) that say not to use on plastics, and others like LifeSeal (r) that are specifically for plastics.

Best of luck.
Deposit $.01 please, with Monday discount,
Loren in PDX

 

[larossa]

I'm in the process of also replacing my gate valves with seacocks. Just one question, when installing the thru hull to the seacock do you use the retention nut?

 

[Loren Beach]

Definitions...

larossa,
I may be misunderstanding the question, but you may be talking about somewhat-unrelated plumbing parts.
To me, a "seacock" is a plug or ball valve in one assembly integral with the flange base that mounts directly to the backing plate inside the hull.

The threaded thruhull comes with a flange-nut (retention nut) that holds it on the inside, and then a separate valve is threaded onto that fitting. In that situation (and that's the way Ericson did it on our boat in '88) the valve is supported only by the the threaded thruhull tailpiece.

Surveyors have always told me this method was weak and subject to being broken off by movements of tools or stores sliding around the nearby bilge. (i.e. it might not pass the "kick test")

Regardless of construction material, the flanged seacock design is far stronger than a valve screwed onto the tailpiece of the thruhll.
You can see pictures of several brands of flanged seacocks in other threads on this site, FWIW.

Loren

 

[NateHanson]

I'm in the process of also replacing my gate valves with seacocks. Just one question, when installing the thru hull to the seacock do you use the retention nut?

In a word, no. If you're using a flanged seacock (as opposed to a ball valve) then you won't use the retention nut that came with your new thruhull.

Nate