Bronze verses Stainless Steel through hull fittings/valves

[Peter]

My current through hull fittings and valves are “plastic”, no info on what material etc and my best guess have been installed since new, approx 1983 (did they have “plastic” fittings in 1983?). No info/history from previous owner if he changed them. My questions are
-At the moment they are not giving any problems, are they OK to leave considering there life.
-If I change what are the differences between fitting bronze or stainless steel through hulls and valves. With respect to life, electrolysis etc. Preferred option would be s/steel as I have a ready source of s/s valves.

Thanks

Peter

 

[narooma]

Recently changed my original (1980) through-hull fittings to upgrade the instruments. Absolutely nothing wrong with the old ones and much better quality. Only the size created the problem.

 

[narooma]

Recently changed my original (1980) through-hull fittings to upgrade the instruments. Absolutely nothing wrong with the old ones and much better quality. Only the size created the problem. The old ones were the 'plastic' type.

 

[tazzle]

The one possible weakness of plastic through-hulls came home to me when I recently refitted Raedwald and replaced a couple (with DZR bronze). Faced with an absolutely tight fitting well-sikaflexed in plastic fitting that no wrench would turn, in a flash of inspiration I gave the side of the 'nut' an experimental blow with a wood chisel and mallet. Hey presto, it sprang open. I tried the same on a second one - again, the nut split immediately. Fitting removed in under a minute.

It did make me wonder though if they're under that much strain how easy it would be for one to split when the hull is working under the effects of a lively sea.

 

[Salty John]

The only acceptable 'plastic' seacocks are made of Marelon (trade name, supplied by Forespar) which is a Dupont glass reinforced plastic called Zytel. If yours say Marelon or Zytel (also Xytel) on them they should be OK.
Stainless steel is controversial for below waterline applications so I'd avoid it. Best non-plastic choice would be bronze or DZR ball valves with chromed ball and neoprene seal.

 

[rogerthebodger]

The current practice on steel boats is to weld a stainless steel nipple to the hull and screw a stainless ball valve onto the nipple.

On my new steel yacht I have used stainless steel through hull screw on fittings with ss (316) ball valves. This also means all material below the waterline would be simular galvanicly except the prop so galvanic protection would be less of a problem

IMHO stainless ball valves would also be easer to obtain at reasonable cost as industry uses the alot.

 

[boatmike]

Glass filled plastic hull fittings have been around for a long time. I think the only reason why they are not popular is the suspicion that they are not very strong and could break. Certain types of plastic do get brittle with age but I am not an expert.
I would however say that if you replace them use proper bronze in preference to stainless that has IMHO no place below the WL. In some cases there is an economic argument for using 316 stainless for things like propshafts but even then crevice corrosion is common. Bronze is best!

 

[catalac08]

regardless of the stainless versus bronze debate IMHO metal is best - a boat in Wales sank on its pontoon a few yeaars ago. The reason was found to be a plastic through hull fitting that was sheared off cleanly at the hull. It was thought that the hull had touched the corner of the pontoon on entering the marina berth and unluckily had sheared off the fitting.

 

[boatmike]

This has in fact been done by some boatbuilders for years but is by no means a "current standard practice" As far as I am aware there is no Lloyds or DNV approved proceedure for doing this and it is not current practice on any steel vessel carrying Lloyds approval. Certainly it is good practice to "collar" a hull fitting with a substantial internal backing but stainless steel is susceptible enough to crevice corrosion without welding it and creating an inter metallic compound that would be even worse.

 

[rutten]

Roger, on my steel hull all SS weld-ons cause galvanic corrosion. I wonder how you protect SS fittings on steel against that?

 

[Gunfleet]

Just a little note about under the waterline fittings

I gave myself a nasty shock recently. The galley sink outlet on my boat (above the waterline) is very difficult to access. It drains into one of the cockpit drain fittings, also very inaccessible (and below the waterline). Recently I decided to clean the drain out - I'd never done it. I managed to push the sink drain pipe off and the sea began to come in. Though the sink is above the waterline, when the drainpipe comes off it (the pipe) falls below the waterline. And it had just been push fitted. It gave me a cold sweat. I have owned the boat for some years and never noticed. My excuse is that is very difficult to see, much use that would have been, mid North Sea. The surveyor who did the boat when I bought it hadn't spotted it either.