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Old 22-09-2006, 09:45   #1
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Thruhull fittings

Anyone have a current, good source for thruhull fittings? I am hauling my Cascade 42 next month and need to replace a few and want to replace more. This boat has way too many for my current setup. Any suggestions, short of permanantly glassing them in, to seal some of these holes? I'm debating a double plate set up. It seems this would have a lower chance of failure than a valve and still allow easy reversal should I add things later, like a watermaker or genset


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Old 22-09-2006, 11:01   #2
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Aloha Steve,

Most folks like to get rid of as many holes in the hull as possible and fiberglass in as they remove thruhulls. Less holes, less worries about valve or fitting failures which could sink your boat. If you add more gear later then a manifold system using an already installed thruhull, valve, and strainer seems to make more sense rathering than drilling a hole for another thruhull.

I like the marelon valves and thruhulls that most supply catalogs have. You might just call the Cascade folks to see if you can get an opinion and a discount if you order through them.

Kind Regards,


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Old 22-09-2006, 15:57   #3
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Steve K,
You didn't mention how many of your thru-hulls are in-takes and how many are out-takes. As John said, in takes can be reduced by manifolds (just a series of Ts strung together). I reduced 6 intakes (engine, generator, frig, head, galley and anchor washdown) to three via manifolds. One manifold serves the engine and generator and a second serves all but the washdown pump. The thru-hull for the washdown is in the bow and connecting it to one of the manifolds would have required running hose most of the lenght of the boat, so I left it alone.
Out-takes are a different problem as many of them are sink drains distributed around the boat and combining them might make for very slow draining sinks. Also you want the head out-take away from and down stream of the intakes and not combined with any other out-take.

I would recommend that you remove any unnecessary thru-hulls and glass in the hole.

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Old 22-09-2006, 17:23   #4
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It's not so easy when you think about redundancy. This summer we had very high jelly fish and through hulls were glogging left and right. You can use a mnaifold but you need a larger through hull to feed it. But in fact it may glog up just as easy as one.

When you put all the eggs in one basket you need to take extra precaitions. Elimination of through hull is not bad but leaving an option open is not something to toss away. One plastic trash bag and everything is shut down. If the through hull was unnecessary then why was it there in the first place?

So you have one through hull and 25 extra hose clamps and 30 extra feet of hose. Those are just as serious risks as a hole in the boat when connected to the grand daddy hole in the boat. I don't see it as that easy. Any junction could fail rsulting in the same accident as a through hul failure. It has to be that way otr the one hole is too small. Now what if the one big hole fails? A small hole might just get you by for a time. A big hole won't.

The logic only works if you can eliminate ALL holes. Now that would be an idea worrth the effort.

Combining holes that don't get used at the same time is clearly a good idea, but when you opt for the bigger hole to get rid of other holes I'm not so sure.
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Old 23-09-2006, 06:47   #5
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Permenently glassing in the holes is the way to go. Any other set-up is ugly, unprofessional and has about the same chance of failure as leaving in the old valve.

When I glassed in my old thru-hull holes, I ground out a depression on both the inside and outside of the hull. I used epoxy resin and fiberglass and essentially made a glass/epoxy rivet where the hole used to be. The hole itself was filled with little fiberglass circles and the depressions filled with larger circles cut from roving and mat.

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Old 23-09-2006, 11:32   #6
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When you use a manifold you have only one strainer to clear of nettles not many. I cannot see any additional risk of one big hole in the vessel (e.g., 1.25") versus 3 small ones (3/4").
I do agree that there is no point in going to this expense if your are not also modifying something in your seawater plumbing (adding/removing one or more systems, fixing a problem, etc.). To install a manifold to just reduce the number of thu-hulls is probably not worth doing. In my case I had several intake seacocks, each difficult access and each with an equally difficult to access strainer. I ended up with one moderately difficult to access seacock and one very easy to access strainer.

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Old 23-09-2006, 15:10   #7

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"If the through hull was unnecessary then why was it there in the first place?" Wouldn't you agree, it usually was done that way because that was the cheapest way to build the boat?<G> Owner wants a head, you add one. A sink, you add one. Telling a worker to make a hole and add a drain, is cheaper simpler than designing a sea chest for all options.<G>

Steve, surely someone makes mushroom-headed dummy caps to plug through-hull holes? Like a big carriage bolt that you can bolt & seal in place with a high quality adhesive caulk? Of course you still have the usual worries, metal can corrode, FRP (like real marelon) theoretically can crack or burn...

Might be easier (or at least more secure) to haul the boat and just glass 'em all over "properly" if you're not going to install replacements.
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Old 23-09-2006, 17:29   #8
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Good thread ! My Bristol has more thru-hulls than I would prefer, but none are unused and there is no easy way to combine or pipe to a seachest. My approach is to carefully inspect all thru-hulls and replace when needed. This past spring we replaced three. I expect this to be on our project list every year. My original thru-hulls were old method (bedded in epoxy). New method is to actually thrubolt the thru-hull. A new bronze thru-hull thrubolted and properly bedded is, IMO, a safe condition and not something I worry about. Of course - I have plenty of plugs.



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