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saurav16 05-30-2007 10:54 AM

Replacing SeaCock Gate Valve with Marine Ball Valve

My boat has gate valves for the freshwater intakes one for the head and the 2nd for the freshwater intake for the engine. My surveyor told me that I should replace the gate valves with Marine Ball Valves for safety. I think it will be a pain to remove the old gate valve since its flush with the floor and connected to the through hull.
My question is would it be possible to keep those gate valves in open position and just add the marine ball valve right behind it so the series goes Hull==>Gate Valve (open pos)==>Marine Ball Valve?

can you use something like this|51|106370|813148|319675&id=102487

jmunson2 05-30-2007 11:15 AM


Although certainly no authority on the subject, my personal opinion is that you wouldn't want to do that (from experience with plumbing for ponds/waterfeatures, etc.).

The gate valve is not as good as the ball valve. I'm willing to bet the current ABYC standards dictate the use of ball valves.

R&R with a ball valve would be a better choice.

The reason NOT to do as you suggest is that it doesn't solve the problem (if, indeed, it is a problem) the surveyor points out, and also overcomplicates things.

The KISS rule definitely applies on a boat.

Bite the bullet, and follow the surveyor's recommendation (if indeed you must) and you will be better off.


/s/ Jon C. Munson II

T34C 05-30-2007 12:00 PM

I unfortunately just went thru this with my fresh water intake for the engine. It really isn't as hard as it may sound to replace the whole thing. I started backing off the old gate valve and it just kept turning. Come to find out the original "thru hull" didn't have a flange on the outside and was really nothing more than a piece of bronze pipe glassed into the hull. I ended up spinning out the whole thing. ground down the inside of the hull to match the outside contour. (was 4 in. thick) Used a half round file to enlarge the hole to the desired size. Installed new thru hull with lots of 5200. After that set up I then put the ball valve on and reattached the plumbing.

Whole thing took maybe a half day total time. Did it the week prior to the boat going in the water. No problems.

Gary M 05-30-2007 02:39 PM

I agree you should take the gate valve out and maybe even the through hull to at least inspect it and rebed it properly. If you have a cored hull check that the opening is properly sealed.
However I assume your boat is on the hard, I would not mess with a old through hull and valve in the water. Murphy is still out there!


saurav16 05-30-2007 10:59 PM

Yeah I will be doing this repair on the hard. I guess its not too bad to do. But did if you are putting a seacock did you use wooden pieces between the seacock on the inner side of the hull? Or did you use glass?

T34C 05-30-2007 11:07 PM

I was lucky in that there was already marine plywood glassed into the hull as a backing plate with LOTS of glass over it. Thats what made the hull 4 in. thick in that spot.

Maine Sail 05-31-2007 07:20 AM

If you have..
If you have a gate valve threaded onto a through hull and the through hull does not have a flange you need to replace the whole thing. This is a commom "lazy way" of installing through hulls and is not supported by most insurance surveys and is also not ABYC or Coast Guard recommended.

The problem with buying a through hull, sticking it in the hole with 5200 then threading the nut onto it and then threading the valve, gate or ball, is this. Through hulls are what they refer to as straight thread meaning the threads are NOT tapered like the NPT threads of a gate or ball valve. In most cases you are lucky to get two or three whole turns down the threads of the through hull before it starts moving thus possibly breaking the seal. These threads are NOT meant to be threaded together. The straight threads of a through hull are meant to be threaded onto a flanged sea ****!

A seacock, the proper way of keeping water out, is a tapered valve or a ball vavle as made by either Apollo, Groco or some others who have them made by Apollo or Groco and it has a built in flange. These valves are made from silicon bronze and NOT brass! When installing these you must bolt them directly through the hull with a sufficient backing block. This does two things it gurantees a solid mount that can't be "snapped off" by a heavy item in rough weather, or by lightning and it guarantees that the through hull won't spin, breaking the seal, when you are changing the 1.5 inch odor safe hose attached to it. You are alo NOT dependant on two or three threads when trying to micky mouse a combination of straight threads and NPT threads. If you must use a threaded on ball valve Groco makes a bronze flange with male NPT threads! No one makes a through hull with NPT for a reason!!!

saurav16 05-31-2007 07:44 AM

Thanks for the post, I was wondering though the through hull with the flange has to be mounted on wood to get a level surface, and bronze screws need to be drilled through the hull right? Won't there be a leak the screws are going through the hull? Also If the wood gets wet that the ball valve is sitting on it will swell and rot so there won't be a good seal there. Should you use glass instead of wood?

camaraderie 05-31-2007 07:57 AM

Wood (marine ply or Teak) is fine but once you have it "fitted" well to the hull form then coat it with epoxy to avoid deterioration and then bond it to your hull using 3M 4200 or the equivilent. Note that the screws into the wood are just to keep it from turning. the real strength of the application is from the compression of the screw threads.

Maine Sail 05-31-2007 07:57 AM

I laminated and made a 1/2 inch thick fiberglass board onto a sheet of glass that was waxed. I then drilled 6 inch round "donuts holes" with my hole saw and drill press. These donut holes are my solid glass backing plates. Yes it's more work but it's the right way to do it. Once I had my donut holes made I roughed the interior hull surface with a brass brush on my drill and also roughed the "rough side of my donut holes. I then mixed up a batch of fiberglass "kitty hair" and installed my backing plates. I used the small hole saw guide hole to put a threaded rod through so I could tighten everything down and I'd have a perfectly aligned and smooth as glass backing plate. Once the glass was cured I went outside and with my hole saw drilled my through hull hole.

Yes the screws go all the way through the hull but you counter sink them then apply 4200 or similar. Once that has cured for a day or two skim over the countersunk bronze bolts with West System and cabosil or 3M Blister Repair Putty. They don't leak if done correctly. On certain hulls like some Hunter's you may not have enough thickness to counter sink properly so in this case I would laminate more thickness on the inside of the hull so you can counter sink properly..

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