View Full Version : Thru Hulls & Seacocks
07-22-2001, 03:04 PM
I have a Canadian built salmon troller (plank on frame). It is fastened with steel boat nails. There are several unused/corroded thru hulls with gate valves that I plan removing. Also, I'm adding a cabin which will require putting in thru hulls and seacocks for the head. I can't use the old head thru hulls due to the distance from thru hull to head (40 ft).
Now, my question. What is a good method of plugging the old thru hulls? Should I be concerned with bronze thru hulls and dissimilar metals (the steel fasteners)? Are the marelon fitting worth using? I'm a Neo-Luddite and, afraid of plastic. Also, any hints on installing seacocks would be appreciated.
Thanks in advance - Terry
07-22-2001, 05:05 PM
Terry,the failure of thru hull fittings sink more boats than all the other reasons combined.You are quite right to be very careful.
Buy the best quality marine bronze fittings.
They will not be a problem in causing action with the steel fasteners,especially when properly bedded.Use ball valves and stay miles away from gate valves.The last thing you want is a gate valve hung open by debree in an emergency.Ball valves require periodic attn.etc.but they are a thousand times more reliable than gates.
If it were me,I would plug the holes with a butt block type of approach(epoxied and screwed.)On the outside,a round plug epoxied in and faired to the hull.
These are the guiding points I followed from my regular boat yard and this forum a couple of years ago.
Cant speak to installation hints.Have too little exp.to have developed a system.
Hi Terry, Do as Dasboat suggests, go with bronze for your fittings and ball valves with monel trim. The plug and (backing block (butt block) approach for curing your old thru hull ills is the way to go unless you want to replace the plank anyway. Many people tend to deferr replacing planks with thru hulls in them because of the added expense of monkeying with the thru hulls, consequently these planks can be very deteriorated. Hopefully the plank(s) in question is OK. Give me a call at the yard or swing by and I'll give you some pointers with regard to fab, fit and installation.
[This message has been edited by RGM (edited 07-22-2001).]
07-24-2001, 12:12 PM
I had 8 thru hulls when I took over my 35' sloop. All good bronze, some not in use. Some capped w/ bronze pipe cap. I did away with 2 of them, plugged hole as Dasboat suggests, with lead sheet tacked w/ copper tacks and bedded in 5200 on the outside. I replaced one outside patch that had been done this way 10 years ago, mostly to see what kind of shape it was in -- it could have lasted another ten w/ no problem.
I had one bronze gate valve with the stem corroded off - handle would free-wheel, gate not moving, stuck open. Junk that sucker, or save it for Exhibit A about why not to use gate valves. Old Wilcox seacocks with tapered plug are pretty reliable - if not corroded or de-zincked -- and available used, cheaper than the new stuff and just as good I think. They want regular exercise and lube - water pump grease. If they dribble a bit you can get by with lapping them with valve grinding compound till the plug makes a tight fit - careful to not go too far so the plug sinks into barrel enough to spoil the alignment of the bore.
You need a "step wrench" for all this -- the gizmo that backs the through-hull out, using the internal lugs in the bore -- Steveston Marine got mine for me.
07-24-2001, 12:16 PM
By the way Terry, I am glad you have taken on one of those great old wooden trollers - enhances my appreciation of BC waters a lot to see one around now and then among a sea of white gel coat covered shoe boxes . . .
07-25-2001, 12:17 AM
Terry - as you know I have the same type of situation as you. I removed 2 thru hulls several years ago and did the trick as described above. In my case I temporarily screwed a piece of plywood to the inside of the hull over the hole. I then used a hole saw that would just slip thru the hole and ran the pilot drill thru the ply. I then used a slightly larger saw to "clean" up the inside of the hole and give me clean wood. Then a cedar plug, also cut with a hole saw, on the drill press and with no pilot drill, was epoxied into the hole using a backing block of cedar planking that was screwed down with about 8 good screws. Its been several years now and during my hull scraping jag I tried to remove the backing block with no success what so ever - its bonded AOK !! I scraped the bottom paint off the outside to have a look and it is in great shape.
Go for it !! Remove them all and use a wooden bucket !! Besides it suits our boats !!
07-29-2001, 01:22 PM
Thanks for all the info. One thing nobody mentioned is what they used for bedding/sealing. Dolfinite? Sikaflex?
John shared his experience with mixed metals (bronze / stainless). I purchased Groco bronze seacocks. The instructions that came with them said to install with stainless steel fasteners per some ABYC standard and, to bond...
07-29-2001, 01:28 PM
I use sik.and except for the stuff being messy,like the results.
On the subject of gate valves versus ball valves - when I first insured Emilie, the insurance company sent out a person to survey the boat. The man quite rightly insisted that I change the through-hulls and valves, which were old and badly corroded. When I said I would install ball valves, a look of horror appeared in his eyes. - Ball valves have a hole through the vital part, he said, - and when you close the valve, that hole will be full of water. When it freezes, it will expand, but there is no room for it to do that - and the valve may disintegrate because of the internal pressure... I duly installed gate valves, which of cause are so inconvenient to operate that users of the heads can't be bothered to close them - and if the flip-over valve on the marine toilet is left in the wrong position, the boat sinks (which is what I wanted to prevent in the first place). The insurance man was more than a bit odd in other respects - what I want to ask is if anybody has experienced blown ball valves because of frost, or if the man just has a bee in his bonnet (if that's the right idiom).
07-30-2001, 11:35 AM
I guess he could have a point,but my $ is on the wasp in his bonnett theory.
There is a lot of lore about these things.Maybe some of the pros.have had some experience with this issue.
07-30-2001, 01:26 PM
The Groco ball valve seacocks have drain plugs to drain any water when you winterize. If used, that would prevent any damage due to freezing.
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