Adding deck hardware to deck with plywood core

[David B]

Originally Posted by jimp1234

I need to add some deck hardware but my boat is a seventies vintage with a plywood cored deck. So some questions. Should I consider over-drilling the holes needed for the hardware, filling with epoxy, then drilling the correct size hole through the epoxy? If yes what epoxy would you recommend? Would West System Six10 work? For backing plates I'm thinking about using G-10. Any better options? Also any rule of thumb for sizing the backing plate? For instance for a 6" deck cleat I was considering a 6" x 6" sheet of G-10 if I can make it fit below deck. And I just went through the thread about the butyl options given that Bed-It is not currently available, so I'm thinking about the butyl sold by SailRite, or maybe going with Sikaflex 291. TIA

-Jim

This or similar. It is a very thin epoxy. First coat thin 50% again, then 25%, then neat. I saturates into the timber making water ingress impossible. It used also to come with fungicides, but then the chemical police put a stop to that (we couldn't be trusted .......).

It is still my go to product for any timber I am drilling or screwing into. Make the hole/screw the screw in, then remove drill/screw, and with a syringe full of Everdure, fill the hole and watch it sink into the timber. Repeat until no more is absorbed, let cure then insert bolt/screw/fitting, whatever - bedding down as appropriate with Sika.

https://www.international-yachtpaint...imers/everdure

[s/v Jedi]

Originally Posted by Spot

Thanks. I made a little graphic to see if I understand all of this correctly. Most of my hardware was installed like sample A. What I have taken apart, at a bare minimum, goes back together with fresh butyl and bigger washers.

Silver=Stainless or other metal
Green=Butyl
Black= Rubber O-ring (Mike's method above)
Yellow= Plain drill and fill and redrill
Red= Core removed drill and fill and redrill
Gray and brown fabric=: GRP (fiberglass)

Please advise if anything is amiss on the picture.

I’m guessing B is aluminium backing plate? That needs to have rounded corners and roundover edges as well. You don’t need that much roundover radius, I like 1/8” roundover bit.

Also, you put fiberglass on top as well in C? I never did that. The countersink and O-ring is great but you can do that straight into the deck. If your too layer fiberglass is very thin then yes you can use fiberglass. I would use 1/8” thick and cut it in the shape of the cleat on top with 1/8” reveal. Epoxy it onto the deck.

[Spot]

Originally Posted by s/v Jedi

I’m guessing B is aluminium backing plate? That needs to have rounded corners and roundover edges as well. You don’t need that much roundover radius, I like 1/8” roundover bit.

Also, you put fiberglass on top as well in C? I never did that. The countersink and O-ring is great but you can do that straight into the deck. If your too layer fiberglass is very thin then yes you can use fiberglass. I would use 1/8” thick and cut it in the shape of the cleat on top with 1/8” reveal. Epoxy it onto the deck.

Thanks Jedi, I guess I should explain my starting points for the drawings.

-Sample A is my boat as found and sort of a 'how not to do it' example. I probably should draw some rot in the plywood to bring that idea home.

-Sample B is the hypothetical next level better with butyl, epoxy, and a backing plate. I imagine that many of us would install new gear like B using some extra care but maybe not knowing about the backing plate edges, etc.

-Sample C was my attempt to add in all of the ideas up-thread (raised deck plate, o-ring, replace adjacent core with resin, and rounded edges on the backing plate) for an all-up solution.

Maybe we can wait a little and see what else comes up then I can revise the picture in a later post.

[s/v Jedi]

Okay that’s cool. What I like about the thin fiberglass piece above deck is that it lifts the possible point of leaks above the surrounding deck. I am adding 3/16” thick rings under the frames of my hatches when I re-bed them. I also countersink the holes but use a ring formed from the butyl sealant I use.

For your C diagram I would add the washer like in diagram A. I would change it to a heavy gauge fender washer. Places like bolt depot, fastenall etc. have those.

[glenn.225]

Originally Posted by Spot

Thanks. I made a little graphic to see if I understand all of this correctly. Most of my hardware was installed like sample A. What I have taken apart, at a bare minimum, goes back together with fresh butyl and bigger washers.

Silver=Stainless or other metal
Green=Butyl
Black= Rubber O-ring (Mike's method above)
Yellow= Plain drill and fill and redrill
Red= Core removed drill and fill and redrill
Gray and brown fabric=: GRP (fiberglass)

Please advise if anything is amiss on the picture.

Spot
Thanks for the illustration, and the rest of you for the words of wisdom.

I've added it to my fiberglass repair file. Next time someone at the club wants mounting info, I can give them a picture (worth more than a thousand words).

[Chotu]

Originally Posted by Spot

Thanks. I made a little graphic to see if I understand all of this correctly. Most of my hardware was installed like sample A. What I have taken apart, at a bare minimum, goes back together with fresh butyl and bigger washers.

Silver=Stainless or other metal
Green=Butyl
Black= Rubber O-ring (Mike's method above)
Yellow= Plain drill and fill and redrill
Red= Core removed drill and fill and redrill
Gray and brown fabric=: GRP (fiberglass)

Please advise if anything is amiss on the picture.

Whoops. I misspoke earlier.

All my deck hardware is “C” but without an o-ring.

Drill and fill for me involves a correct or close to correct size hole to leave the glass in place, then an Allen wrench in a drill to remove the core, then taping the bottom of the hole and pouring in neat resin to seal off the core and make a place to re-drill.

So much easier to visualize and talk about with Spot’s drawings. Nice job!

[Chotu]

Originally Posted by s/v Jedi

Okay that’s cool. What I like about the thin fiberglass piece above deck is that it lifts the possible point of leaks above the surrounding deck. I am adding 3/16” thick rings under the frames of my hatches when I re-bed them. I also countersink the holes but use a ring formed from the butyl sealant I use.

For your C diagram I would add the washer like in diagram A. I would change it to a heavy gauge fender washer. Places like bolt depot, fastenall etc. have those.

I did this with my hatches out or necessity. The deck curvature was too great to mount hatches so I needed to make trim rings. After doing that, it dawned on me this was the best way to go because water runs right off and doesn’t wait around to get in.

My trim rings are bonded into place with 5200 which is a better material than epoxy for me to work with, obviously.

[GordMay]

[s/v Jedi]

Yes, when there is room for tapering then that sure is the best solution. Unfortunately I find lack of room most of the time…

I don’t understand the epoxy filler in the backing plate…

[Lake-Effect]

Originally Posted by s/v Jedi

I don’t understand the epoxy filler in the backing plate…

... just extra protection against any seep causing rot in the backing plate? Belt & suspenders...

I usually prefer aluminum for backing plates.

[GordMay]

Originally Posted by s/v Jedi

… I don’t understand the epoxy filler in the backing plate…

A gap filler, to smooth/level any uneven surfaces. Also, bonds plate to deck.

[s/v Jedi]

Originally Posted by GordMay

A gap filler, to smooth/level any uneven surfaces. Also, bonds plate to deck.

No it is in the holes for the fasteners. I do not agree with that at all, those holes were drilled at a way too large diameter, requiring the filler. I suspect this is for a backing plate that is too weak to handle the compression forces and they use the epoxy to resist crushing the backing plate.

A G10 fiberglass plate does not crush, nor does aluminum. The fastener holes should be drilled accurately and not oversize.

[glenn.225]

Originally Posted by GordMay

Gord as Jedi pointed out the first image seems wrong the yellow epoxy filler should be in the blue deck portion not the backing plate.

[jimp1234]

Originally Posted by GordMay

It’s often recommended to use a backing plate that is at least 5/8 as thick as the bolt diameter, and to have at least 5/8 bolt diameter edge clearance [more is better, as space permits] around the hardware [cleat, winch, stanchion base, etc] footprint, or bolt holes [for washers].
I standardized on 1/4" thick aluminum [6061-T6?], which is sufficient for hardware fastened with 3/8" dia. Bolts.

Always grind/cut the perimeter edges to a ±45 degree bevel, to avoid point loading, at the edge.

I used West Marine 105 resin, slow or fast hardener, with 406 colloidal silica filler, for the plugs, and 3M “5200" for the sealant. Others will recommend “butyl”, and caution against “5200", and I won’t argue.

For your 6" deck cleat*, I would suggest a 1/4" aluminum [or 3/8" - ½" G-10 Fibreglass c/w Fender Washers] backing plate, at least 8" long, and 2" wider than the cleat base.


* Depending upon it's intended application, and available space, consider going to a larger cleat. Undersizing is the major defect, I found /w cleats.

First of all thanks everyone for your thoughtful comments. I had one follow up question regarding the sizing of the backing plate. GordMay mentioned above that for my hypothetical 6" deck cleat he's recommending the backing plate be 2 inches longer and wider that the "footprint" of the cleat. My question is if this deck cleat was meant to handle mooring lines, snubbers, etc. basically something needing to support a higher load would you increase the size of the backing plate? Intuitively it would seem that for deck hardware supporting higher loads go with a bigger backing plate, however maybe this is not really necessary. TIA


-Jim

[Lake-Effect]

Originally Posted by jimp1234

My question is if this deck cleat was meant to handle mooring lines, snubbers, etc. basically something needing to support a higher load would you increase the size of the backing plate?

Is that what you are installing - deck cleats for shorelines, mooring etc?

In this case, the load on the bolts and the deck is mostly sideways... aka shear. For this, the 'normal' size backing plate should be ok. But I would do a particularly good job of removing core from the deck holes and filling that in with epoxy with fiber filler, so that the deck holes are better able to withstand the sideways pressure from the bolts when the cleat is loaded up. And maybe epoxy the backing plate on, too. This is all to transfer the sideways load to more of the deck.