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Old 18-10-2019, 18:10   #1
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Thru-Hulls in cored fiberglass. Is core removal and backing required?

Many months ago, a company installed a thruster system on my boat composed of 4 pumps. Each pump has an intake, and those intake fittings were installed through solid fiberglass. Each pump is connected to 2 nozzles, which were installed through cored fiberglass.

When the company installed the nozzles, they drilled a hole through the cored hull and installed the nozzles. I'm fairly sure they put a thin layer of resin around the exposed core.

Since the installation, we have had 5 leaks, and I recently found 4 more leaks. Only one of these leaks is on a nozzle. The company agreed to fix the leaks. This is great, but there are quite a few costs that I need to cover, such as dockage and accommodation rental while we are on the hard.

So we are getting hauled out a 5th time, and I'm trying to understand if these nozzles should also be removed and if the core material around the hole should be replaced with fiberglass.

I'm really keen to get this all figured out and NOT have any more leaks after the install.

I've found a number of articles; all suggest that the core should be removed around all thru-hulls. I've also spoken to a couple of surveyors, and each also suggested that the core material should be replaced with fiberglass -- some thought it was especially important because the nozzles vibrate as water is pushed out through them (to generate thrust).

We found a surveyor who is coming by the boat to have a look and provide his assessment. Another expense -- but I hope this will give me some "credibility" when the topic of nozzles comes up.

Thoughts?

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Old 18-10-2019, 18:28   #2
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

Dig out the core 1/2 all around and fill with thickened epoxy. I use colloidal silica. Did they paint over the masking tape?
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Old 18-10-2019, 18:32   #3
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

The leaks are not directly connected with the treatment of the core, but the treatment of the core is awful.

It certainly looks like the installer either did not know what he was doing, or just decided to do a cheap-ass job. Leaks just should never happen on a properly installed through hull fitting, much less NINE of them. I don't know why they leaked, other than the installer did not know what they were doing.

There is no excuse for leaving core exposed as shown in your photograph. No, a thin wipe of resin is NOT sufficient. The coring needs to be dug out and replaced with thickened epoxy so there is NO possibility--None--of water getting into the core, even if the fitting leaks. When I do a job like this, at least an inch of core is removed, and more if I can. It strengthens the whole structure, which is especially important for a thruster nozzle. There are many ways of doing this, and we can argue about the best one, but ALL of them are better than what you got.

I hope the original installer gave you a really cheap price for the install, because they gave you a really cheap job. And the left on masking tape is just a double extra laughable job.
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Old 18-10-2019, 18:34   #4
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

I would have thought removing the core and filling with epoxy filler would be enough since it is gluing the two hull skins back together.
I have never seen thru hull holes fiberglassed, mainly because it is a real SOB to fibreglass upside down. If you insisted I would do a combination of filler and fiberglassing. Using Uni-web S glass wetted out I would (after removing the core) first smear the inside of the hole with epoxy filler then push the wetted out glass fibres into the filler. That way the wet fibreglass should not sag down from the top of the hole. I am not sure this is really achieving anything more than straight filler, but at least the filler will not crack.
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Old 18-10-2019, 18:35   #5
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

Boy sure looks like they did
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Originally Posted by Training Wheels View Post
Dig out the core 1/2 all around and fill with thickened epoxy. I use colloidal silica. Did they paint over the masking tape?
I am sorry to hear your problems! I am also in the camp of digging out the core. It's a small task that WILL give me the confidence that no coring will rot - especially in the hull where core damage can cause a loss of the vessel and potentially lives.

I would be on them as to why they chose not to remove the coring. Backing plate would also be a nice thing to have but that will depend on how the thruhull is fastened
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Old 18-10-2019, 18:43   #6
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

Everybody above is correct.

As to the cored hole, it depends how great the core thickness is as to how far in you dig. I prefer 1.5 times the thickness if possible and I use random glass fiber as the filler and the silica as a modifier to the resin. On a large hole such as this I like to see glass fiber because there could be bending loads on the new port. If it is filled with neat resin and silica only it will be hard but brittle. Your installer was not competent or they took an enormous short cut. The original job would eventually leak into your core.
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Old 18-10-2019, 18:44   #7
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

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Originally Posted by chowdan View Post
Boy sure looks like they did

I am sorry to hear your problems! I am also in the camp of digging out the core. It's a small task that WILL give me the confidence that no coring will rot - especially in the hull where core damage can cause a loss of the vessel and potentially lives.

I would be on them as to why they chose not to remove the coring. Backing plate would also be a nice thing to have but that will depend on how the thruhull is fastened
I wish I would have done more research on through-hulls and how they should be installed. I suppose.... I now known


Quote:
Originally Posted by Training Wheels View Post
Dig out the core 1/2 all around and fill with thickened epoxy. I use colloidal silica. Did they paint over the masking tape?
I've gotten all sorts of recommendations. Most of the feedback as been to removed at least 3/4" + the size of the through-hull fitting, and backfill that.

And yes, they bottom painted over the tape. I gave up at that point... it was the least of my worries. Haha.


Quote:
Originally Posted by billknny View Post
The leaks are not directly connected with the treatment of the core, but the treatment of the core is awful.

It certainly looks like the installer either did not know what he was doing, or just decided to do a cheap-ass job. Leaks just should never happen on a properly installed through hull fitting, much less NINE of them. I don't know why they leaked, other than the installer did not know what they were doing.

There is no excuse for leaving core exposed as shown in your photograph. No, a thin wipe of resin is NOT sufficient. The coring needs to be dug out and replaced with thickened epoxy so there is NO possibility--None--of water getting into the core, even if the fitting leaks. When I do a job like this, at least an inch of core is removed, and more if I can. It strengthens the whole structure, which is especially important for a thruster nozzle. There are many ways of doing this, and we can argue about the best one, but ALL of them are better than what you got.

I hope the original installer gave you a really cheap price for the install, because they gave you a really cheap job. And the left on masking tape is just a double extra laughable job.
I believe most of the leaks are due to... (1) the replacement of parts, that requires quite a bit of force, breaking seals in other parts... (2) insufficient sealant... and (3) insufficient cure time. You're right... we agree... my leaks aren't connected to the "core" question.


Quote:
Originally Posted by Fore and Aft View Post
I would have thought removing the core and filling with epoxy filler would be enough since it is gluing the two hull skins back together.
I have never seen thru hull holes fiberglassed, mainly because it is a real SOB to fibreglass upside down. If you insisted I would do a combination of filler and fiberglassing. Using Uni-web S glass wetted out I would (after removing the core) first smear the inside of the hole with epoxy filler then push the wetted out glass fibres into the filler. That way the wet fibreglass should not sag down from the top of the hole. I am not sure this is really achieving anything more than straight filler, but at least the filler will not crack.
Cheers
It was my understanding that the core would be replaced from the inside, so the fiberglass work shouldn't be upside down. Maybe maybe I've been sniffing too much solvent
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Old 18-10-2019, 19:00   #8
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

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It was my understanding that the core would be replaced from the inside, so the fiberglass work shouldn't be upside down. Maybe maybe I've been sniffing too much solvent
You can remove the inner skin for a distance around the hole, and lay up glass to replace the core. That is a certainly a premium job, but is likely overkill.

The core can easily be dug out with a variety of tools, and the the resulting gap between the skins filled with thickened epoxy. That's the way 95% of all properly installed holes in cored decks or hulls are handled.

Another option is to remove the inner skin, install a piece of G10 in thickened epoxy, and glass over that to replace the inner skin. Another very strong way of doing the job.

I assume that the manufacturer of the thruster system has recommendations on how they should be installed in cored hulls? I would certainly be on the phone with them. If they are a reputable supplier they might be very interested to know if this was an "approved" installer taking these kinds of incredibly negligent shortcuts, and (if you are really lucky) might be willing to help fix the problem.

As I said, there are multiple ways to skin this cat, but NOT the way the installer of your gear did it.
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Old 18-10-2019, 19:19   #9
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

The tape just slays me.

But if it makes you feel any better after reading this I am going to have to pull all my portholes out again because I didn't even think about the core. Ugh it took so long.
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Old 18-10-2019, 21:32   #10
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

If you get a qualified surveyor to testify for you, I think it's quite likely you'd recover all expenses up to the small claims limit in your state. That is pretty shabby and amateur work
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Old 18-10-2019, 23:38   #11
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

Textbook solution the only correct one:
circular taper on the core for 4-5“ ending min 2“ before hole, then fibreglass. Every halfway reputable yard installs seacock-throughhulls this way. Much more load on the thruster nozzles, so beefier, not shoddier installtion required.
You got superfluous equipment installed by idiots or crooks.
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Old 18-10-2019, 23:59   #12
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

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Originally Posted by ttex View Post
The tape just slays me.

But if it makes you feel any better after reading this I am going to have to pull all my portholes out again because I didn't even think about the core. Ugh it took so long.
oh hey, me too, but because I didn't read the installation instructions correctly before installing all ten portholes. IT TOOK ME SO LONG THE FIRST TIME :|

OP, out of interest, what was the system you had installed? I can't figure out what would need 8 new thruhulls. Some kind of propulsion?
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Old 19-10-2019, 03:49   #13
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

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Originally Posted by Nicholson58 View Post
Everybody above is correct.
As to the cored hole, it depends how great the core thickness is as to how far in you dig. I prefer [at least] 1.5 times the thickness if possible ...
Indeed.
In addition to sealing the core, the backfill also provides compressive strength.
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Old 19-10-2019, 04:46   #14
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

Quote:
Originally Posted by double u View Post
Textbook solution the only correct one:
circular taper on the core for 4-5“ ending min 2“ before hole, then fibreglass. Every halfway reputable yard installs seacock-throughhulls this way. Much more load on the thruster nozzles, so beefier, not shoddier installtion required.
You got superfluous equipment installed by idiots or crooks.

I'd agree with that. That is the way I have done all my sea-cocks and I wasn't aware of any other way. I wonder what the ABYC Standards are?


If you want to recess a through hull on a cored boat, take a deep breath and steel your nerves: here’s how to do it.
Remove the through hull and the seacock. Get your new flush-type through hull, and get a hole saw the diameter of the flange of the through hull fitting. Hole saws, designed to fit the chuck of a drill motor, are available at any large hardware store. Sizes are usually available in 1/16” increments. Note that a different size hole saw is required for every different size through hull fitting, so by now you’re going to have to spend some money. A hole saw arbor costs about $8, the hole saws about $8 to $12 each. A $2.99 multi-sized hole saw from the discount store may get you through one hole, if you never think you’re going to use it again.


The balsa core has been removed and replaced with solid glass around this through hull, preventing the possibihty of water rnigrafion.Now comes the scary part. Cut a hole through the outer skin of the boat, concentric with the existing hole for the through hull, that is the size of the flange of the new flush through hull fitting. Don’t cut through the inner skin!
Next, dig out the core material around your cut for a distance of an inch or more, cutting back with a sharp knife or chisel. Clean the remains of the core material thoroughly from the inner surfaces of both fiberglass skins. What you are going to end up with is a solid glass section of hull in the way of the through hull fitting, and you want to remove all traces of core material that might inhibit the bond between the hull skins and the new glass you put in.


https://www.practical-sailor.com/news/Through-Hull-Fittings-10445-1.html
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Old 19-10-2019, 05:38   #15
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Re: Thru-Hulls in cored fiberglass. Is core removal and backing required?

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If you get a qualified surveyor to testify for you, I think it's quite likely you'd recover all expenses up to the small claims limit in your state. That is pretty shabby and amateur work
That's a good idea. Unfortunately our costs are already above the $20,000 mark and the small claims limit is $5,000 here.
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