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Old 10-08-2020, 08:07   #1
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Does Thru hull in sandwich core need epoxy?

Hi,

I have removed an old thru hull under the galley with the intention of fitting a new one and I've found that the hull is a sandwich construction with a centre layer of wood.

So the question is why did the person who fitted the previous thru hull not epoxy over the wood first?

I would expect that to have been done, not just to caulk over the lot.

Thankfully, there is no evidence of leakage and the wood is dry, so I will at least give the exposed wood a coat of epoxy and a thin layer of thickened epoxy before fitting the new thru hull...

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Old 10-08-2020, 08:09   #2
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Re: Does Thru hull in sandwich core need epoxy?

Quote:
So the question is why did the person who fitted the previous thru hull not epoxy over the wood first?
because he was lazy, cheap, or uninformed.

Why did the previous owner of my boat use automotive wiring and busbars? See above.
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Old 10-08-2020, 08:10   #3
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Re: Does Thru hull in sandwich core need epoxy?

definitely seal the core with epoxy. water ingress into your wooden core would be catastrophic to your hull integrity.......some people just dont know.
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Old 11-08-2020, 01:02   #4
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Re: Does Thru hull in sandwich core need epoxy?

That's kind of what I thought, but I'm new to this bosunry business, so thought it worth checking...

Thanks guys...

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Old 11-08-2020, 05:21   #5
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Re: Does Thru hull in sandwich core need epoxy?

When I added an additional through hull / seacock to my boat w/ a multiple layer cored hull, I drilled slightly oversize, scooped out the coring, filled the hole w/ West System epoxy w/ filler, allowed to cure, redrilled the hole at the correct size then installed the parts, as-shown in their fiberglass manual, on pages 47 and 48.

When I barrier coated my bare hull, I first removed all the below waterline parts, to permit application of epoxy up into all the holes.
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Old 11-08-2020, 05:50   #6
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Re: Does Thru hull in sandwich core need epoxy?

I recommend you use a small drum sander (Dremel tool) to remove some of the wood core. Next, replace that with some epoxy or vinylester filler (like https://www.amazon.com/3M-46012-Mari...74KS726DPZXTT5
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Old 11-08-2020, 06:04   #7
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Re: Does Thru hull in sandwich core need epoxy?

You may want to replace all the fittings...... if one was done incorrectly you may find the rest are as well. I would gouge out the wood core and fill with a thickened resin.

Good luck!
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Old 11-08-2020, 06:54   #8
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Re: Does Thru hull in sandwich core need epoxy?

I have been repairing and building boats as a marine professional for over 10 years and you absolutely MUST REMOVE THE CORE in 99% of applications for any bolts and especially through hulls.

The removed core size should allow you to easily access all the fasteners required in the application you working on.
-----------------------
On your hull, based on the description, you will want to use a hole saw about 1-2 inches over sized of the through hull to remove the inner laminate skin and coring.

Then you will bevel your edges at a 3-1 ratio based on total thickness.

Last you want to measure: Top laminate thickness + bottom laminate thickness + 20% and add this laminate structure to the hull where the core was removed.
------------------------
Although overkill I believe this job can be dramatically simplified by purchasing pre-fabricated fiberglass panels (or making your own) from Mcmaster Carr, FGCI, or anyone else.
Simply purchase the pre-fabbed solid fiberglass panel the same thickness as your core- hole saw to remove core, same holesaw on the fiberglass panel, bed in epoxy and glass it over to the same laminate thickness as your current top laminate at the recommended 10-1 ration (10X the top laminate total thickness= distance of lamination coverage from cut edge).

There are also specially design coring for bolts/through hull installation. Piedmont plastics sells a few. These are very high density solid plastics design for adhesion to common resin systems. Sometimes you can order samples and substitute this for your current wood coring- which mean you do not have the tedious job of beveling your edges.

Only install bolts into a SOLID laminate structure, never a cored structure or you will crush the core, either instantly or over time and cause water ingression, drips, core saturation, delamination spreading.. etc.

Just FYI: 16 layers of 1708 is 3/8" when done under vacuum bag or pressed under
clamps/weights.
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Old 11-08-2020, 08:44   #9
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Re: Does Thru hull in sandwich core need epoxy?

No need to over complicate. you need a fibreglass tube with ID slightly larger than your fitting, Easiest to make your own by wrapping plastic film round your fitting and lay up fg. round it. Enlarge the hole in the hull to accommodate your laminated tube, bond in place with thickened epoxy. Grind flush when cured, bed fitting with mastic of choice.
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Old 11-08-2020, 09:08   #10
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Re: Does Thru hull in sandwich core need epoxy?

I've used both a rabbiting bit on a router and an allen wrench with a chisel tip ground into it. This cuts back enough to allow filling with a peanut butter consistency of epoxy thickened with high density filler. For bolts if you have them drill oversize holes from the inside and not through the outer skin of the hull. 3/4" hole for a 1/4" bolt. Fill with epoxy paste as above let harden and then drill the 1/4" holes all the way through.
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Old 11-08-2020, 09:09   #11
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Re: Does Thru hull in sandwich core need epoxy?


See how it is done in the Airmar manual.
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Old 11-08-2020, 09:10   #12
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Re: Does Thru hull in sandwich core need epoxy?

http://www.airmar.com/uploads/Instal.../17-364-01.pdf
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Old 11-08-2020, 09:55   #13
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Re: Does Thru hull in sandwich core need epoxy?

[QUOTE=
------------------------
Although overkill I believe this job can be dramatically simplified by purchasing pre-fabricated fiberglass panels (or making your own) from Mcmaster Carr, FGCI, or anyone else.


.[/QUOTE]

How does this product compare with G10?
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Old 11-08-2020, 10:01   #14
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Re: Does Thru hull in sandwich core need epoxy?

A Dremel with a small router bit is great for removing some of the core between the two glass layers. Then fill with thickened epoxy.
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