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Discussion Starter #1
Hi, I have a thruhull that had a Groco SV-1500 seacock in it. It was original on my 1981 C&C. The wood backing plate started to rot and the valve was leaking a bit when you tried to open or close it, so I pulled it out. I'd like to replace it. I was thinking of going with the newer Groco seacock system with a flanged adapter and inline ball valve.

As a novice I am a bit nervous about having to go from two bolt holes in my hull to 3 and having to drill new ones. Can anyone recommend the best way to make those holes and what is the best material to use as a backing plate so I don't have to deal with rotting wood again?

Any insight would help me a lot!

Thanks,
Shaun
 

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You don't necessarily need to thru bolt the flange adapter thru the hull. I can't say for sure what you have on your boat, but on mine I never had the bolts thru the hull. I'm replacing several similar thu hulls and I've been communicating with groco. What they suggested to me is to 5200 the backing block to the hull and use lag bolts to screw down the flange adapter. The flange adapter is a great new way to do this from what I've studied up on. Groco phone support is pretty good and helpful.
So that would mean all you need to do is fill the existing holes with epoxy filler. Mainesail will tell you to glass in your backing plates and that has merit but the 'standard' practice seems to be gluing them down. I soaked my marine ply backing plates with wood hardener just because.
 

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Use fiberglass for the backing plates. You can make up your own backing plates relatively easily if you have epoxy and fiberglass. See Maine Sail's project pages for instructions on doing the installation.
 

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Discussion Starter #4
Thanks for the info guys. I really like the idea that I don't have to make new holes in the hull for the bolts! This just became a project I am much more comfortable with.
 

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Dont forget to reseat the thru hulls while your at it. I would replace the valves and absolutely use the flange adapter. It will be so easy to change or fix the valve later, if you have to.
 

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You don't need to through bolt..

If you use a fiberglass backing block you can drill & tap it and install bronze studs before epoxying it to the hull. This avoids the necessity of completely through bolting and offers near the same strength. With a thick epoxy coated wood backer you can drill and install bronze lag screws.

Personally I don't like wood but done right it can last for a while. If it swells and shrinks, which it does, it can lead to failures of the sealant sooner.
 

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Discussion Starter #8
Thruhulls Installed!

Well I just finished installing the backing plate and flange today! I was nervous taking on this project but I think it came out great. Here are pictures of the two thruhulls installed. One is for the cockpit drains and the other is for the galley sink. I just need to do a couple more things and this project is set. I want to sand down the surrounding area and paint with interprotect, replace the stainless nuts with bronze (they were supposed to come in today but didn't get delivered yet), and install the valves and hoses.

Thanks for all the tips!


 

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Very professional looking. They should all look like that...even from the factories.

I just found after launching an A/C thru-hull that is weeping from under the bed of sealant. Installed less than 5 years, with an untreated wood block and an unbonded bronze valve. Not very pleased at all.
 

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What to do for thru-hulls smaller than 3/4"?

I'm replacing all my thru-hulls and will use flange adapters according to the Maine Sail website. Groco only makes the adapters down to 3/4", and I have two smaller diameter (1/2" & 3/8") thru-hulls to replace.

I'm wondering if anyone knows of a distributor that makes marine bronze seacocks for sub-3/4" thru-hulls? ~Joel
 

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I just had this same situation Joel and decided to upgrade my two 1/2" holes to the 3/4" Groco size. One was my engine raw water intake that coupled with a 5/8" hose, and so the 1/2" thru hull was the constriction in the system and I figured 3/4" would give more flow. The other was my head water intake and it also mated to a 5/8 hose and so the same rationale. Bigger hole=kinda bad. Bigger hole=better water flow=parts that fit=kinda good. Good luck.
 
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