Sea Cocks on a Steel Boat

[Petronella]

I want to replace some of the sea cocks on Petronella. The boat, a Joshua, is steel and the sea cocks are installed above the water line on the end of vertical steel tubes welded to the hull. The old ones have been there some years and although they look OK I think it is time to examine them and replace them if required. I'm not sure what steel the current ones are made of but what would you use to replace them with? DZR and Marelon look to be the options I think. If it was a GRP boat I would go for DZR but is the plastic Marelon a better option for a steel boat?

Thanks for your views.

John

 

[TimBennet]

You can gasket and isolate DNR or bronze sea cocks on flanged steel standpipes, including any joining bolts. Threaded joins are almost impossible.

Then check with a continuity meter that there is absolutely no electric connection between the steel and the valve.

But far better (in every sort of boat) is to use the Marelon valves. Someone will be along to tell you that these won't survive a fire, but I have yet to see a yacht that is still habitable after a fire of sufficient intensity to destroy Marelon valves.

 

[KellysEye]

Marelon is the way to go on a steel boat, our boat was steel and that's what we had. The issue is that they are nomally attached and sealed to the hull with a tightenin ring outside the boat. I think there is isn't a version that can be attached to tubes but I suppose you could cut the tubes off.

 

[Rossynant]

Don't cut the tubes! They are there so you don't have to worry about pipework or seacock failure
I've seen plastic valves screwed on such pipes, probably Forespar. Looks similar http://www.forespar.com/products/boat-marine-plumbing-ball-valve-thru-hull.shtml

 

[PCUK]

My 26 year old steel boat has the original bronze sea-cocks in contact with the steel. The huge steel area protects the sea-cocks but because the area of the sea-cock is so small it has no real effect on the steel.

 

[ribrage]

I want to replace some of the sea cocks on Petronella. The boat, a Joshua, is steel and the sea cocks are installed above the water line on the end of vertical steel tubes welded to the hull. The old ones have been there some years and although they look OK I think it is time to examine them and replace them if required. I'm not sure what steel the current ones are made of but what would you use to replace them with? DZR and Marelon look to be the options I think. If it was a GRP boat I would go for DZR but is the plastic Marelon a better option for a steel boat?


Thanks for your views.

John

My steel boat has a similar set up, with raised steel tubes which are welded to the hull and threaded for the sea cocks which are screwed onto the steel pipes as per normal, I had one which was in poor condition and decided to replace it , it was there for nearly forty years .

Using a combination of angle grinder, Dremel and a drill , I removed the old pipe which was in better condition than I thought, I replaced it with another piece of steel tubing and welded it into position as before, if you keep your anodes replaced routinely it won't make a great deal of difference what way you do the job.

If these last as long as the others I'm a happy man , plus i have the knowledge the sea cocks are above sea level !

 

[Petronella]

Thanks for all your replies. I will probably go for the straight through Marelons as shown on most of this page http://www.asap-supplies.com/marine/non-metallic-valves as my first choice. Hopefully I can prepare and thread the ends of the existing upstands (after inspecting them internally) and just screw the new valves straight on with the correct size Marelon hose tail to take the hose away.

 

[KellysEye]

>Don't cut the tubes! They are there so you don't have to worry about pipework or seacock failure

I don't understand that, if a seacock fails it doesn't matter if it's on a pipe or not.

 

[prv]

I don't understand that, if a seacock fails it doesn't matter if it's on a pipe or not.

Yes it does!

If it's on a standpipe, then a) no water will leak in due to the failure (assuming the boat stays more or less level in calm water) and b) you don't need to lift out to change it. Just unbolt the old one and bolt on the new. Always seemed like a good robust technique to me, though I do wonder about potential corrosion and fouling inside the steel pipes which would be hard to get at.

Pete

 

[Rossynant]

though I do wonder about potential corrosion and fouling inside the steel pipes which would be hard to get at.

Insides in no worries Straight tube, no problem to poke into. Stainless tubes may be welded on, stainless pieces are often used for small details or edges in steel boats.
But heard of boat that had such tube break off from bottom - corrosion on the weld probably, not from inside of tube - from inside of bilges... Boat was corroding from inside anyway, and this spot is very difficult to clean rust off and repaint, not to mention awkward place to make a weld so might've been compromised.
Idea of tubes is a nice one; we did it on a GRP boat once for cockpit drains, laminating tubes up integral with hull. Best would be to laminate the whole drains right up to cockpit sole, but with GRP deck being elastic it was made to just below, good margin over the waterline, and connected with rubber tubes - without the seacocks. Such arrangement was one of approved methods in safety rulings here.
Incidentally - technique for laminating them: long candles were inserted through the holes and laminated over; then it's enough to pierce them or drill through and push out; remains washed out with boiling water.

 

[prv]

But heard of boat that had such tube break off from bottom

Nasty!

In the article where I first read about this technique, it was suggested that standpipes should be brought up close to bulkheads, or half-height partitions, to which they should be welded for additional support.

Pete

 

[Rossynant]

I don't think it was any disaster (would probably heard more interesting details about), as the boat was still sailing later on