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Old 04-06-2017, 14:10   #1
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Leakless Composite Decks - Your: Thoughts, Successes, & Failures

I'm curious as to what folks have done in terms of making their composite decks, or portions there of, leakless. Such as using G-10 as core, & blind tapping it for hardware fasteners. Meaning drilling holes through 90% of it's depth, & tapping & threading it for them. And then only using bedding compound underneath of the hardware to mitigate any small movement, if any, in the hardware. Or fully epoxy bonding the fasteners into the tapped holes.

It would seem that mechanically speaking, G-10 has the structural properties to handle this in all but cases involving the highest loads, or shock loads. So I'm curious to find out who's used it for what in the above mentioned manner.

It works with aluminum, & steel, so why not composites? G-10 has mechanical properties on par with a lot of aluminum. And plenty of hardware gets bonded in place sans nuts on the fasteners. Heck there's a whole section on it in The Geugeon Brothers: On Boat Construction. So were I to be rebuilding a deck, it certainly would be an attractive option.

Where would/have you used it, for what, & how big of a success or failure was it for you? Also any tips on techniques, or regarding where not to use it would be appreciated.

I know that personally, in the past, I've done this on many many bits of hardware pretty much automatically. Everything from mainsheet travelers, & winches, to casting pads for ultra high load items. I'd draw the line at bonding in keel bolts, & maybe deck cleats. The latter based on deck laminate thickness in the area, & what thickness of G-10 I could use in the sandwich.

However the test loads for fasteners bonded into wood, & composite & structural laminates seem to bear out it's viability. With the laminate often (usually?) failing prior to the fastener being pulled out, if it's epoxy bonded in place.

Which, if the are in question is new construction, or a rebuild of it, then there's little reason not to design the laminated/core layup to be able to have hardware attached in this manner, non?


I'm looking for lower maintenance, leak free, deck ideas here. AKA ways to "boycott" things like 5200, & Sikaflex, as much as possible.
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Old 04-06-2017, 19:47   #2
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Re: Leakless Composite Decks - Your: Thoughts, Successes, & Failures

For production boatbuilding at least, there is no substitute for through-bolting. Anything else is a false economy, not least of all for the loss of confidence in surface fastenings in high stress areas and situations. I can't think of a single instance on a sailboat where I would not through-bolt, with backing plates--- maybe a flag halyard or bimini adjusting cleat? In a steel or aluminum hull, possibly non-thru bolts might be acceptable but I'd want double the thread depth for steel and at least triple for aluminum before I felt comfortable in any situation. With any composite, I don't know where I'd feel comfortable, but the thickness would surely out-weigh the practicality.


Of course I'm just old school, conservative and mean (cheap). And surely there are times when one has to resort to face fastening, and there the standard practice of epoxy with milled fibers, drilled and tapped is hard to beat. I've used it many times, but never in an instance which I would call critical.

Nor would I try and tap threads directly into G10 for high load situations. I've done it before, in regular fiberglass too, and the appliances held, but no way am I trusting it for a high stress situation...

As for the sealing issues with through-bolting, well that's just one of the compromises...5200 is evil stuff, so maybe butyl tape of bedding compound is in your future, though I wish I could find out what the still-soft-after-40-years bedding compound they used around the portlights on my boat was....
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Old 05-06-2017, 02:13   #3
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Re: Leakless Composite Decks - Your: Thoughts, Successes, & Failures

I've always been more concerned with protecting the integrity of my cored deck from moisture and rot than worrying about a drip down below. Leaks can generally be cured with rebedding. Over the years I have managed to over drill most of the deck fastener holes and fill with thickened epoxy before redrilling and rebedding.
I use G10 for things like rot proof pads around my chainplates but prefer to rely on throughbolts with backing plates or washers and nuts rather than blind taps.
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Old 05-06-2017, 03:32   #4
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Re: Leakless Composite Decks - Your: Thoughts, Successes, & Failures

Besides all of the above stated reasons why this is a bad idea, from a practical standpoint I have to say really? Installing the G-10 as a core material in the sandwich? Accurately and precisely drilling and tapping blind threads by hand somewhere on the deck of a boat where nothing is plumb or level?
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Old 05-06-2017, 20:14   #5
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Re: Leakless Composite Decks - Your: Thoughts, Successes, & Failures

Quote:
Originally Posted by UNCIVILIZED View Post
I'm curious as to what folks have done in terms of making their composite decks, or portions there of, leakless.

However the test loads for fasteners bonded into wood, & composite & structural laminates seem to bear out it's viability. With the laminate often (usually?) failing prior to the fastener being pulled out, if it's epoxy bonded in place.


I'm looking for lower maintenance, leak free, deck ideas here. AKA ways to "boycott" things like 5200, & Sikaflex, as much as possible.
I have a fiberglass-reinforced epoxy deck that replaced the teak deck. I through-bolt everything. I have never had any leaks from any part of my new deck or the equipment through-bolted to the deck. The new deck is about 15 years old. I replaced all teak pads with starboard pads. This includes windlass, cleats, stanchion bases, propane locker pads, etc.

I can not think of anything that is not important enough to through-bolt. It's fine to trust stress tests in a controlled environment. But after months of flexing, pulling, heating, and cooling; I like knowing there is a through-bolt with a backing plate or fender washer. Just my thoughts.

I NEVER use 5200 and find very few uses for it. I don't consider it appropriate for through-hulls, or much of anything else. ...
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