Blanking a through-hull (skin fitting)?

[nigelmercier]

I've got a through-hull fitting at the bottom of my hull that I no longer use. I'm not keen on patching it as cutting a 12:1 chamfer in GRP that is over 25mm is going to be huge.

Are there any blanking fittings that are suitable, preferably plastic?

[DawnTreader]

If you have access from the inside you can lay up the appropriate thickness and diameter inside without grinding a bevel. Then you can apply thickened goop from the outside without all the fairing.

[pcmm]

Originally Posted by nigelmercier

I've got a through-hull fitting at the bottom of my hull that I no longer use. I'm not keen on patching it as cutting a 12:1 chamfer in GRP that is over 25mm is going to be huge.

Are there any blanking fittings that are suitable, preferably plastic?

If you do the bevel from both inside and outside, you cut the thickness of the chamfer in half. its not that bad! I've done 6 so far on my boat and have 4 more to do!

[UNCIVILIZED]

To the OP, regarding your question. 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?

Originally Posted by DawnTreader

If you have access from the inside you can lay up the appropriate thickness and diameter inside without grinding a bevel. Then you can apply thickened goop from the outside without all the fairing.
Attachment 124034Attachment 124035

I get that the hole is likely small. And said area probably isn't a deal breaker for the boat's structural integrity, but... What happens if/when that section of the hull later gets used for mounting something which creates a significant load? Or when said area of the hull gets slammed by a big wave, etc.?

How then, do you figure that you can "get away" with doing such a patch/repair? Particularly one sans bevel, or proper glass work?
And what do you mean by "thickened goop" on the outside? As aside from such goop being non-structural, it's going to require a bit of fairing itself. Non?

A bevel is pretty much critical when doing such repairs & modifications. As such glasswork generally tends to be structural. I mean the hull is a inch thick there. Pprobably for a reason.


That said, the entire patch & bevel, needn't & probably shouldn't be entirely on one side or the other. But rather, you put some of the bevel (for the scarf), both on the hull's inside & on the outside. Ditto with regards to the new laminate.

Preferably applying the glass from both sides of the hull, while the new laminate is still wet, or in the green phase; so as to get your chemical bond. While the 2-sided bevel, & patch, creates a mechanical lock to the repair (or patch).
And yes, I'm aware that doing a layup which is that thick, all in one session, probably isn't wise, due to the probability of an overly thick stack going exothermic.


Is doing it in that manner a pain in the rear? Yep, most likely. Will anyone but you ever know? Doubtful perhaps.
Albeit when I found a similar area, where I gather that there'd once been a through hull, on my first boat. Which was filled with inch thick Bondo, right at the turn of the bilge near the keel. It was a bit troubling.
Because it surely made me wonder if there were other, similar, yet to be found spots on the boat.
Plus, yes, fixing it correctly added a few days to my time in the yard, for a "simple bottom job". But better that than to leave the Bondo in place, I figured.

And I'm asking the above questions not just to sate my own curiosity. Or to be flippant. But so that those new to boats, or composites/composite repair in general, get the full (& correct) information. Including other options, besides the glass worth which I just described.

[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.

I had one on the boat I just bought that's been plugged for over 20 years. It was really nice to still have the thru hull and operating valve there for the new head's freshwater intake when I needed it.

[Sailmonkey]

Originally Posted by DawnTreader

If you have access from the inside you can lay up the appropriate thickness and diameter inside without grinding a bevel. Then you can apply thickened goop from the outside without all the fairing.
Attachment 124034Attachment 124035

No offense, but no way in hell would I endorse this for a below the waterline hull patch.

For starters, there is surface contamination on your prepped patch site.

The patch itself is simply a piece of glass glued on top of existing laminate. Temporary fix.....sure.




Sent from my iPhone using Cruisers Sailing Forum

[tankersteve]

Slight drift, but can you do half the bevel recommended from the outside, and then lay on thicker layers over the top on the inside? Bonded, but not faired, more like a series of bandaids on the inside of the hull? Wouldn't it be just as strong (ie, the same chemical bonding with the hull, just not beveled in)?

Not doing this type of job right now, but curious about options in doing it 'right'.

Tankersteve

[mikecambrai]

I always put new seacoks made of a glass composite material. This eliminates the problem that might occur over time with electrolysis. If I then did not need that seacock, I would attach a peace of flexible pipe and plug the pipe with a plastic solid tube. Security is then via at least 2 jubilees.
On wooden boats I have just cut a tapered plug and hammer it home with some mastic. On steel of course,I just weld it.

[artisanmach]

There are hundreds of thousands of fiberglass boats sailing around with patched holes in their hulls with no problems... just do a good quality repair and keep things really really clean.

[TurninTurtle]

do it right...

Or plan on needing a bilge pump that can keep up with the hole

[TrentePieds]

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.

I had one on the boat I just bought that's been plugged for over 20 years. It was really nice to still have the thru hull and operating valve there for the new head's freshwater intake when I needed it.

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.

TrentePieds

[UNCIVILIZED]

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.

I had one on the boat I just bought that's been plugged for over 20 years. It was really nice to still have the thru hull and operating valve there for the new head's freshwater intake when I needed it.

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.

[UNCIVILIZED]

Originally Posted by tankersteve

Slight drift, but can you do half the bevel recommended from the outside, and then lay on thicker layers over the top on the inside? Bonded, but not faired, more like a series of bandaids on the inside of the hull? Wouldn't it be just as strong (ie, the same chemical bonding with the hull, just not beveled in)?

Not doing this type of job right now, but curious about options in doing it 'right'.

Tankersteve

No, it's a good question, & well worth asking. Especially as it relates to proper composites repair, & some of the "why" behind commonly accepted & taught practices.

I wouldn't recommend the kind of patch which you're speaking of. But rather, I would go for the full, measured out, bevels, if not bigger ones.
This is because a repair that has properly (measured off &) ground bevel. Is stronger for many reasons. The theories behind them having several key points:

-- Assuming that you’ve properly cleaned the surface first; so as not to grind any contaminants into the surface, which will interfere with getting a good bond strength. And you're using a clean grinding disc. Then you’re exposing clean glass, which now has a good tooth to it, to bond to.

-- With the multi-layered stack of patches used, starting with the smallest on being applied first. Each layer of added cloth has it’s own area around the section being fixed, to be glued onto. And a wide bond line for each layer of glued on reinforcement allows it to adhere that much better; because of the generous surface area for it to attach to.

A Great demonstration of this, complete with how to pics; can be found in Hooker & Minaret’s thread on Keel Sump/Stub Repair. Check out their laminate “maps”/patch size schematics. Plus how they prep each piece (layer) of reinforcement that they're going to apply... In accordance with their mapped out layer diagram.

-- With this kind of reinforcement stack, that starts with the smallest pieces of cloth first, used in a scarfed in (beveled) patch. In theory, the loads from each layer of the old glass, are pretty much tied in in a direct path, with each layer of new glass.

And if you think about it, which makes more sense? Having the loads in the new glass start out above the glass which they're replacing. And then traveling down over a sharp edge, through the patch's center, & then back up over a sharp edge, & onto the other side.
Or... you can go to a scarfed in patch, where the load path is essentially a straight line. Or one which matches those in the hull fibers surrounding it anyway.

-- Also, with such a patch, as opposed to the “Band-Aid” style that you described. The patch’s flex characteristics, strength, & load paths, will be pretty much akin to those of the surrounding glass. This, without creating any hard spots in the area being fixed. As might, & generally do, form at the edges of non-scarfed in patches.

Kind of like when you sew a piece of new’ish denim, as a patch, onto the holes in the knees of your favorite (worn) jeans. And in pretty short order, the original fabric of the jeans begin to tear at the patch’s edges. As it’s a stress riser, AKA hard point. Where the new fabric is much stronger than that which it’s attached to.
Similar to this, but that's a simplified example.


There’s more to it than this. But the above hits most of the key points. Off of the top of my head anyway. And some great tools for learning more about this topic, & other composite repair & construction basics. Are available (for free download) at the WEST System site. With more/others on System Three Resin’s home page. And most other resin/reinforcement makers & retailers. To include; project examples, how-to videos, free periodicals & downloadable articles & books, ad infinitum.
It’s good stuff, for the most part. Even including a lot of what you’ll find on YouTube.

Hope that helps to answer things

[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

[barnakiel]

I have filled the old thru hull with foam/3M, then added one layer of fine glass and resin on the outside. I left the old seacock in the closed position and removed the handle.

There are bronze, brass and SS screw on plugs too. I have not seen plastic ones, check googling for 'marelon' caps.

Neat grp work simplifies things if you want to use the area inside for e.g. storage or tankage. An old thru hull will always be 'in the way'.

b.