Blanking a through-hull (skin fitting)?

[UNCIVILIZED]

Originally Posted by Jim Cate

I am left with the idea that folks are over thinking this job. Seems to me that there are two aspects to sealing up the hole left by a skin fitting: keeping the water out and maintaining structural integrity.

All the worry about the strength of a patch seems needless, for the boat has been working well with the hole in the hull all along. The skin fitting adds nothing to the structural strength. Why is there now a worry about hull strength? In fact, grinding out a big 12:1 chamfer and then relying on secondary bonds for the patch may result in a over all weaker structure than before.

Keeping the water out is, of course, quite necessary! Most of the plans suggested should work, including using a blanking plug. If a permanent glass repair is done, the major concern is having a good bond and preventing leak paths from developing. The strength is, IMO, a minor issue. If the hole is in an area subject to significant flexing attention to the bonding becomes more important, and in that case the blanking plug becomes a good solution for it does not depend on bonding to remain watertight.

I realize that this view seems at odds with the practices involved with repair of damaged FRP hulls, but to me, the situations are different and require different solutions.

I have donned my Nomex flame suit...

Jim

Jim, what you're saying makes sense, 100%+ And all of it ran through my miind when composing those other bits. I just ran out of energy to compose any more text that would have paralleled much of your statements above.

As stated, I simply wanted newbies to know that there was some incorrect info being propogated, & why. Ergo, my overcramped fingers, from too much typing on that subject.

[pcmm]

All valid points, the point of glassing in the thruhull is to avoid the possibility of the fitting rotting off at a later date.

Using epoxy its really easy to make a secondary bond that is as strong as the original. grinding the bevels really isnt hard work and doesn't have to be super accurate. just cut the bevel on both sides to be roughly correct. This also serves to reduce the size of the overall bevel you need to make and fair in later! non of it is hard. I use West's technique of building the entire patch on the table and installing it like applying wallpaper! Use some "peel ply" ( or Dacron dress lining) and the patch will come out pretty darn smooth to begin with! all really simple and effective techniques.

[tinkrman69]

I wouldn't take a thru-hull/seacock out to put in a mechanical plug. It stands just much chance of failing as the seacock. a 25mm hole hhmmm just over an inch.

take a tapered wood plug uut in the hole from the outside mark it. pull it out and cut it at the mark. measure the thickness of the hull at the site and cut the plug to that thickness. coat it with epoxy and drive it tight into the hole. 45 minutes. come back tomorrow morning and grind the area down...glass and plug...about a 1/4" 6mm. the patch area will have a diameter of approximately 4" using 1.5 oz mat tear..not cut..a peace just bigger than the plug, then do that 4 to 5 more times consecutively bigger each time till you reach the edge of the ground area. about two hours. wait another two to three hours and go inside and grind that area making the wood plug flush with the surrounding area and roughing the surface about 3 to 4 inches in diameter. say two layers of 1.5 oz mat on that, after about 30 minutes paint it with gelcoat. two hours. go outside and fair the patch and...if the hull has been barrier coated...barrier coat it. if not gell coat it. Schatch it tomorrow with 120 sand paper and bottom paint the hull. Splash it in the morning.

if the ambient temp is betwixt 75 and 85 with polyester resin use 6 to 7 drops of hardener per oz of resin if it's above 85 use 5 drops. mixing no more than 4 oz at a time. You can do the metric math.

most people are intimidated by such a job. It's really simple. That repair will last as long as the hull will. which is longer than ANY fitting will last. I mean think of it. Why are you taking the fitting out? Any job worth doing os worth doing right. Short cuts always come back to bite you or the next owner. which still will tack a chunk out of your Karma.

Lance

[pcmm]

Originally Posted by tinkrman69

I wouldn't take a thru-hull/seacock out to put in a mechanical plug. It stands just much chance of failing as the seacock. a 25mm hole hhmmm just over an inch.

take a tapered wood plug uut in the hole from the outside mark it. pull it out and cut it at the mark. measure the thickness of the hull at the site and cut the plug to that thickness. coat it with epoxy and drive it tight into the hole. 45 minutes. come back tomorrow morning and grind the area down...glass and plug...about a 1/4" 6mm. the patch area will have a diameter of approximately 4" using 1.5 oz mat tear..not cut..a peace just bigger than the plug, then do that 4 to 5 more times consecutively bigger each time till you reach the edge of the ground area. about two hours. wait another two to three hours and go inside and grind that area making the wood plug flush with the surrounding area and roughing the surface about 3 to 4 inches in diameter. say two layers of 1.5 oz mat on that, after about 30 minutes paint it with gelcoat. two hours. go outside and fair the patch and...if the hull has been barrier coated...barrier coat it. if not gell coat it. Schatch it tomorrow with 120 sand paper and bottom paint the hull. Splash it in the morning.

if the ambient temp is betwixt 75 and 85 with polyester resin use 6 to 7 drops of hardener per oz of resin if it's above 85 use 5 drops. mixing no more than 4 oz at a time. You can do the metric math.

most people are intimidated by such a job. It's really simple. That repair will last as long as the hull will. which is longer than ANY fitting will last. I mean think of it. Why are you taking the fitting out? Any job worth doing os worth doing right. Short cuts always come back to bite you or the next owner. which still will tack a chunk out of your Karma.

Lance

Why can't people just do the repair the normal way? the method above is more complicated and weaker than just doing a normal patch with a bevel ground into both sides of the hull. the method above introduces wood into the laminate where there normally isn't any and relies on chopped mat for the strength of the repair.

just do the repair the normal way people. Its not hard or complicated! even easier if you use 1708 as the mat and glass are already stitched together in a strong unit.

Don't shortcut it, the proper way is actually straight forward and relatively simple.

[artisanmach]

hire a dutch boy with a 1"+ dia. finger...

[fryewe]

I just did a similar project today.

Three quarter inch bronze thru hull mushroom with a 90 (NPS to NPT) on it, followed by a nipple and a bronze ball valve, a nipple, then a reducer to half inch...to supply salt water flushing to the head. I removed the hose when I installed a C-head.

I wanted to remove the valve/nipple/reducer arrangement because it was taking up space in a locker without reward, and the 38 year old installation with no hose attached was a leak waiting to happen.

I considered putting a plug in the 90, but didn't want to leave the NPS/NPT connection in place, so I considered putting a cap on the mushroom, but I couldn't find an NPS thread plug and didn't want to make one.

The issue was solved for me when I tried to remove the piping...my pipe wrench slipped and the mushroom turned, breaking the caulking seal between the mushroom and teak backing plate. The whole thing had to come out.

The NPS/NPT connection was "welded" so I had to cut the mushroom with a multi-tool.

I prepped the hole inside and out with a rasp on the multi-tool (those things are worth their weight in gold). I closed the hole using West System epoxy and cloth and adhesive filler...beveled four to one (which is adequate for a symmetrical one inch hole in the 5/8 inch fiberglass hull). I backed the hole inside with a three and a half inch diameter piece of BS1088 plywood soaked in epoxy, attached to the hull with adhesive filled epoxy.

That was my solution. I believe it will be as strong as the original hull, and I know it will not leak.

[rwidman]

Originally Posted by appick

You could simply install a bronze pipe thread plug into the seacock valve and call it a day. Odds of it leaking are pretty minimal...............

That's what I would do. Or even remove the seacock and install a cap on the thru hull.

[rwidman]

Originally Posted by UNCIVILIZED

Yeah, I had a similar thought. Where I'd take a bronze nut, & thread it onto the through hull. Followed by a pipe cap. After having seriously cleaned all of their threads first. And then use the nut to help lock the cap onto the pipe, like you do with 2 nuts on a bolt, in order to freeze the critical one into proper position.
This, in addition, of course, to Loctiting everything together. Maybe even using Red (Loctite) for once, in this instance, for peace of mind.

Instead of Loctite, I suggest thread sealant. Pipe dope.

[nigelmercier]

Originally Posted by UNCIVILIZED

To the OP... Are you referring to what amounts to a round fitting to replace the through hull with. Who's two halves mechanically thread together, & are sealed via gaskets? So that the hole's then filled by the threaded plug? ...

Pretty much, essentially a skin fitting with no hole in it.

[ranger58sb]

Originally Posted by appick

You could simply install a bronze pipe thread plug into the seacock valve and call it a day. Odds of it leaking are pretty minimal.

Originally Posted by TrentePieds

Exactly! Why "repair" it if it doesn't need repairing? If the old seacock is going south for some reason, then just replace it, and blank it. Then you're good for another 20 years.

Originally Posted by UNCIVILIZED

Yeah, I had a similar thought. Where I'd take a bronze nut, & thread it onto the through hull. Followed by a pipe cap. After having seriously cleaned all of their threads first. And then use the nut to help lock the cap onto the pipe, like you do with 2 nuts on a bolt, in order to freeze the critical one into proper position.
This, in addition, of course, to Loctiting everything together. Maybe even using Red (Loctite) for once, in this instance, for peace of mind.

Originally Posted by rwidman

Instead of Loctite, I suggest thread sealant. Pipe dope.

Originally Posted by nigelmercier

Pretty much, essentially a skin fitting with no hole in it.

What exactly would be the additional benefit you'd expect from doing fiberglass work versus simply screwing in a blanking plug? IOW, why bother?

Our drain plugs are essentially mini-thru-hulls with simple plugs screwed in -- and they never leak. I wouldn't expect a larger thru-hull with an appropriate fitting screwed into it would be much risk...

-Chris

[UNCIVILIZED]

Originally Posted by rwidman

That's what I would do. Or even remove the seacock and install a cap on the thru hull.

The reasoning behind leaving the seacock in place and adding the cap. Is so that you have 2 seperate barriers between the dry side, & King Neptune. I wouldn't be comortable trusting just a cap on a through hull, personally.