Thru-hull skin-fitting type advice

[ruvane]

I intend replacing all my old skin fittings and stopcocks, but I'm undecided as to what to fit as replacements. Firstly the choice for skin fitting is between bronze and suitable nylon/glass-filled fittings. If the "plastic" option is not so great, how come so many transducers use such fittings without serious problems?

If using bronze, why should a stopcock directly attached to it not also have to be bronze to prevent corrosion?

If using "plastic", what is the best method for connecting stopcocks as they obviously cannot be screwed directly to the fitting as with metal ones? Do they necessitate a short pipe from skin fitting to stopcock, then on to the pipe again?

What are the relative merits of gate valves/ball valves/etc?

As you can see, I'm looking for all the info I can gather regarding the choice of fittings.

TIA,
Ruvane.

 

[airborne1]

Technolaser, from 12 years at sea on tankers, other liquid carriers and small boats, NEVER ever use gate valves for a sea cock. ALWAYS use ball valves.
Reason: you cannot tell by looking at the "handle" of the gate valve as to whether it is closed or open or by how much. Also, even with the finest products available, I have seen both manual and remote controlled electric valves jam and/or the opening mechanism/handle break off.
With ball valves, they are operated by a lever. This means that you can immediately see whther the valve is open or shut.

 

[fluffc]

If using bronze, why should a stopcock directly attached to it not also have to be bronze to prevent corrosion?
It does also need to be bronze, to prevent all corrosion. Using Steel/Chromed/Brass fittings will corrode. To get around this, you can bound to a (local) sacrificial anode.

If using "plastic", what is the best method for connecting stopcocks as they obviously cannot be screwed directly to the fitting as with metal ones? Do they necessitate a short pipe from skin fitting to stopcock, then on to the pipe again?
You can get "plstic" seacocks too.

What are the relative merits of gate valves/ball valves/etc?
See answer given above

 

[LittleShip]

By far the best valves are bronze either ball valve or tapered plug.

Gate valves are for central heating and are (IMHO) a poor choice for a boat, but they are cheap!

Plastic (It does have a technical name! I think it's Marelon?) are good on plastic boats but they should not be fitted to any wood boats, although I think the manufacturers will tell you that they are OK.

They should if you use bronze or any other metal be connected to the anodes.

For me it's bronze every time, but we all have opinions!

www.forespar.com/resources2/pdf/marelonPopRed.pdf

Tom