I thought appropriate metal hardware is better for below water fittings? What's the advantage of the valve assembly you recommend over the flanged ball valve assembly? I assume your suggested method includes adhering the backing plate to the hull?
Thru Hull Backing Plates
- Thread starter Project_Mayhem
- Start date
Meh - those Marelon things are bullet-proof, and easy to maintain. I would not worry about that because they are not "cheap plastic" (they certainly ain't cheap). Yes, Ward's approach would include epoxying the backing plate to the hull with thickened epoxy (do it yourself thickening or West Six-10.
The original centerboard was not heavy at all. At times it would get stuck in the slot of the keel because of a buildup of rust inside the iron keel. When I re-installed the keel, I put in a new centerboard of 1/2" steel and made up a mount for a winch and a lead to the cockpit.
The Forespar Marelon Series 93 OEM with King Nut are used by boat builders. The King Nut design provides a 3" flange as part of the valve. The marlin thru hull provided with the valve has a special thread that is very strong.
The real advantage? No corrosion of metals. Some prefer nothing but bronze but then you need to worry about electrolysis. Not with Marelon. And yes, epoxy the backing plate to the hull.
The backer plate above the thru-hull nut is bad.
As for the recess, it looks to me like it could be molded rather than cut out. I’m not familiar with your boat, but is this by any chance a cored hull where they held the core material back from the intended thru-hull location? If so, that would result in such a recess.
Either way, I would cut a G-10 backer plate to fit the recess and set it in thickened epoxy.
Edit: I may have misread the photo in post #15. Misinterpreted dirt from under the old backer plate as a square recess in the hull(?).
As for the recess, it looks to me like it could be molded rather than cut out. I’m not familiar with your boat, but is this by any chance a cored hull where they held the core material back from the intended thru-hull location? If so, that would result in such a recess.
Either way, I would cut a G-10 backer plate to fit the recess and set it in thickened epoxy.
Edit: I may have misread the photo in post #15. Misinterpreted dirt from under the old backer plate as a square recess in the hull(?).
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Here is a photo of the OEM valve I installed last year. It is sitting on 1/4" G10 backing plate epoxied to the hull. I'll be replacing the inline ball valve this year because the 3" king nut base gives the valve a more secure feel when operating than the inline ball valve sitting on a thru hull.
@Dalliance Photos in post 15 and further comments explain it is a hole in the hull liner giving access to the hull. No core in the O'day hulls.
G10 Backer plate was suggested.
G10 Backer plate was suggested.
I'm leaning much more towards using my existing thru hull and valve since I can't find anything wrong with it. It's withstood the test of time but I do see room for improvements in the installation technique
Why is this bad if it has proper clearance?
Backer plate should always be under the thru-hull nut, solid against the hull. It’s there to reinforce the hull.
As a side note if you have never done it: "... cut a G-10 backer plate ..." is easier said that done. That stuff is hardened epoxy/glass and tough as hell. Use a good quality saw and plan to spend serious time slowly cutting it. It eats drills for breakfast.
Absolutely right. It’s dense enough to drill and tap for threaded machine screw connections. I shouldn’t have so blithely said cut a G-10 Backer plate. It’s available precut to backing plate sizes, so check available sizes first and avoid cutting if you can.
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I'm familiar with Mainesail's procedure for thru hulls. After some thought here's what I'm going to do
- Epoxy in a piece of 3" fiberglass that I cut out from another part of the liner to bring the cutout to liner level and seal it off
- Wrap a wood backing plate in finishing cloth
- Rough up liner gel coat and epoxy backing plate in place
- Use existing nut on thru hull
- Seal valve flange to the backing plate
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,121
To each their own path.
The "double" Nuts is nuts in my opinion.
I prefer solid and simple. I would rough up the inside of the existing hole. Clean it. Then apply some shaped layers of wetted fiberglass to build up the depressed hole. This would provide a solid, closed structure to the hull strengthening it where the manufacture weakened the hull.
From there drill the thru hull hole from the outside into the boat through your laid up glass. You now have a one piece strong hole in your hull. Less chance of leakage. Then do your backing plate. Insert the thru hull from the outside with adequate caulking. I like 3M's UV4000 for this task.
The "double" Nuts is nuts in my opinion.
I prefer solid and simple. I would rough up the inside of the existing hole. Clean it. Then apply some shaped layers of wetted fiberglass to build up the depressed hole. This would provide a solid, closed structure to the hull strengthening it where the manufacture weakened the hull.
From there drill the thru hull hole from the outside into the boat through your laid up glass. You now have a one piece strong hole in your hull. Less chance of leakage. Then do your backing plate. Insert the thru hull from the outside with adequate caulking. I like 3M's UV4000 for this task.
- High performance, medium strength bonding allows for disassembly
- Excellent UV resistance
- Color stable sealing
- Above and below the water line applications
Is it recommended to partially tighten the thru hull, wait for the sealant to cure and then tighten it completely?
Your double nut plan creates a theoretical sealed chamber that will fill with water if the sealant at the mushroom head of the through-hull fails. You won’t know about it if your inner seal actually holds for the season. If the water in the chamber can’t drain out, it will freeze during winter storage, expand and damage the hull, crack the fitting or break the second seal, and you will make an unpleasant discovery in the spring. Possibly on launch day.
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jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,121
I did not use that double tighten technique. I was hanging in the slings for an overnight haul. We got the two thru hulls fittings removed and then new ones installed. Tightened the nuts till they were firm and got squeeze out but not all squeezed out caulking from around the inside or outside. Smoothed the caulking around the fittings and left them to cure. Next morning checked the fittings felt sound. Then splashed and inspected the fittings for water tightness. No sign of water intrusion over the past season.
Mainesail did a study on the "partial tighten - cure - retighten" model on his rebedding deck fittings write-up and video. He found that that invites cracking the setup adhesive and it is better to just tighten once when the one-part adhesive it not cured. Post #1 of Bedding Deck Hardware With Bed-It Butyl Tape
BTW: The number of times I have repeated @Maine Sail advice on this forum in the past year, in addition to taking it myself, indicates what a debt of gratitude we all owe Rod Collins. If you have not already thrown in a couple bucks to his Go Fund Me, I suggest paying back now. SailboatOwners.com
It's a catch 22. Both methods have their pros and cons. I get an unbelievably good deal on heated storage