Adding deck hardware to deck with plywood core

[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

[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.

[Chotu]

Gord has good advice above.

*always “drill and fill” (ie: drill a larger hole, tape below and fill with epoxy then redrill at the correct size)

*you are using epoxy as a filler here. It makes no difference whatsoever which kind you use. You could use vinylester just as well for example. Save your money and buy whatever is on sale or reasonably priced. Raka makes excellent epoxy you don’t have to waste money on. They are out of Miami but ship to anywhere. Good support too. I used Raka to fair my boat and to attach things. The hulls were made from a special MAS infusion epoxy and System Three for tying together the cross members with cove joints/fillets. Raka would have been just fine for anything but the infusion simply due to density. I learned this later.

*i like butyl and used it on my deck cleats 5-6 years ago. 2 of those cleats held this high windage 50ft catamaran at anchor while a category 4 hurricane’s eye passed right over the boat. They still don’t leak or drip. I got my butyl at ace hardware or an RV place. I forget which roll I used on those cleats. Suffice to say, it’s not “Marine” butyl. Lol

[s/v Jedi]

For the fastener holes: try to leave the lower layer of fiberglass intact and minimize the opening of the upper layer. Best is to remove core from between the fiberglass layers. You can achieve that with small router or Dremel bits. The small diameter drum sander for Dremel works. You need to remove core for a diameter at least 1/4” more than the fastener hole.

For filling just tape the hole below (if there is a hole at all). Now you need to start with an un-thickened epoxy, like a West System 205 or comparable product from Total Boat, MAS etc. This is a pourable product, nit a squeeze-out product. Add hardener following instructions, then use a small brush or even cotton swab to coat the inside of the opening. It will absorb into the core so repeat a couple of times but don’t fill the hole, just coat it.

If you have enough mixed epoxy, you now need a filler. For casting, a high density filler (like from West System) is preferred. If you use Cabosil (colloidal silica) instead, you need to use less because it needs to stay runny, while Cabosil has anti-sag properties so I would prefer microfiber if no high density filler is available. After masking the deck, pour the epoxy in and use a cocktail stick to stir it and poke it to work all the air out. Make sureit bonds to the underside of the top layer of fiberglass. It the deck is tilted, you may need to wait for cure, then follow up with a thicker mix (Cabosil) to make the top flush with the deck.

For backing plate, 1/4” G10 material or 1/4” aluminum is good foor fasteners up to 5/8” like Gord described. Besides using a roundover for the edges, also use rounded corners so that you eliminate hard spots and stress risers. You can use a woodworking 1/8” roundover bit in a router if you don’t like filing.

[GordMay]

Originally Posted by s/v Jedi

For the fastener holes: try to leave the lower layer of fiberglass intact and minimize the opening of the upper layer. Best is to remove core from between the fiberglass layers. You can achieve that with small router or Dremel bits. The small diameter drum sander for Dremel works. You need to remove core for a diameter at least 1/4” more than the fastener hole...

All good advice, so far.

I used a small Allen Key, in a variable-speed drill, to rout out the core, beyond the perimeter of the hole.

[Bowdrie]

Originally Posted by GordMay

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

The above, from GordMay, is sage advice.
There is an old saying: "Large ropes and small blocks to you". On a 34,000lb boat there are very few applications for a 6in cleat.
I would add; The vast majority of leaks around hardware occur due to the very small distances between the edge(s) of the hardware and the fastener holes.
Any kind of deck hardware, pad eyes/cleats/stanchion bases/etc., ideally should be raised above the deck on a pad of some material.
In the old days Teak was used, today many would opt for something like Starboard/UHDPE/G10.
This eliminates standing water and goes a long way to prevent any leakage, the side benefit is easy cleaning/painting around the hardware.
The top surface of the fiberglass and the underside of the fitting(s) should have small countersinks, this provides a "Doughnut", if you will, where the caulk will not be squeezed out.
Don't drill "exact" holes, no beating on bolts to seat them, depending upon fastener size/length, 1/64>1/32 oversize holes are good practice.

[OS2Dude]

I don't use adhesives to bed my hardware, that is what the bolts are for.

Countersinking the bolt hole for a donut is good advice. I usually drill and tap my epoxy and the backing plate for the bolts I'm using. This is easiest if you epoxy (or even 5200) the plate in place before drilling and tapping so the threads will line up correctly and with the added benefit that the plate won't fall off if you have to remove the hardware in the future.

If adhering the backing plate is not an option, then drill a couple of the holes vastly undersized and use small bolts to hold it in place while you drill and tap the rest. then use the bolts in the holes you just drilled to hold it while you redrill and tap the small holes to the correct size.

[s/v Jedi]

Ah, on sealant. 5200 is good sealant. I just removed keel coolers that had been bedded with 5200 17 years ago and there was no drama removing and dry as a bone (see pictures, the black stuff is 5200).

I do like the butyl sold by Rod Collins but would not use any other (I tried). I do recommend LifeCaulk which is a polysulfide like the 3M 101 that unfortunately is no more.

For the very best seal you can use 1/16” thick neoprene gasket cut to size. I coat both sides in polysulfide and tighten stoutly. Look up general torque table for diameter of fasteners used.

I do agree with the previous poster that tapping thread into fixed backing plate works good but for cleats I would still add heavy gauge fender washer and nylock nuts for mooring cleats. For toerails, genoarails etc. I would trust just threaded fiberglass when it’s at least as thick as the fastener diameter.

[Lake-Effect]

So much good advice here. I've used the same epoxy-filling methods as described on our plywood-cored deck. I favour butyl as a sealant, but it took a couple tries to find a brand (and a batch) that was not so runny.

[Boatyarddog]

Originally Posted by OS2Dude

I don't use adhesives to bed my hardware, that is what the bolts are for.

Countersinking the bolt hole for a donut is good advice. I usually drill and tap my epoxy and the backing plate for the bolts I'm using. This is easiest if you epoxy (or even 5200) the plate in place before drilling and tapping so the threads will line up correctly and with the added benefit that the plate won't fall off if you have to remove the hardware in the future.

If adhering the backing plate is not an option, then drill a couple of the holes vastly undersized and use small bolts to hold it in place while you drill and tap the rest. then use the bolts in the holes you just drilled to hold it while you redrill and tap the small holes to the correct size.

You don't bed your hardware?
That's what the bolts are for, huh.
How do just fasteners keep out water ingress.
Precision fitting?

Boatyarddog

[ausnp84]

We’ve got a ply/epoxy cat, so every single fitting has to be drilled / filled / re-drilled or we inevitably get rot.

Sika 291 is a great sealing material, and clean up with wer / baby wipes is a breeze.

I like the West epoxy as well, with their colloidal silica for a bulking material when mixing the filler.

G10 for backing plates is good also - my last cat was run down by a fishing boat and towed backwards 50nm to the closest port, in 2-4m Biscay swell. The cleats with g10 backing held fast.

Lastly, the advice above re: raising deck hardware is good. Glass a piece of g10 down (or something 5-10mm thick) and it’ll go a long way to stopping leaks.

N

[Mike Banks]

Pretty much what others have said, but I have an extra trick I use which is a second layer of protection. I get a countersink bit and chamfer the holes in bottom of the deck fitting, then do the same in the mating surface on the deck however you arrive at it. When fitting the studs to the deck cleat, slide an O-ring on to each stud, before pushing the studs through the deck.

When the mastic is applied, backing plate is fitted and the washers and nuts tightened, the two chamfered surfaces trap the O-ring and compress it--so it grips the shank of the bolt or stud. Water will not get past that one. If your deck fitting cleat is the sort where bolt heads are visible in the cleat, pop an O-ring between the bolt head and chamfer the top of the cleat a little. O-rings are great little seals. I always have an assortment of sizes and thicknesses aboard.

Since I started doing this I have never had one leak--

[Spot]

Gord, Jedi-
To confirm, you are rounding/breaking the sharp edges of the backing plates that contact the inner skin of the hull as well as rounding them in planshape?

Here's a toast to us poor sailors who have cored boats with nary an epoxied hole and where the orange RTV silicone was spread, you know-around and on top of the washers and nuts, without taking things apart, to keep any more water from leaking in...on the cabin ceiling, over the keel bolts...

[s/v Jedi]

Originally Posted by Spot

Gord, Jedi-
To confirm, you are rounding/breaking the sharp edges of the backing plates that contact the inner skin of the hull as well as rounding them in planshape?

Here's a toast to us poor sailors who have cored boats with nary an epoxied hole and where the orange RTV silicone was spread, you know-around and on top of the washers and nuts, without taking things apart, to keep any more water from leaking in...on the cabin ceiling, over the keel bolts...

Yes, so the G10 is cut out with rounded corners and after cutting, the sharp edges are filed round as well. I use a router with roundover bit for that.

Here’s the pictures I forgot to attach above…

[Spot]

Originally Posted by s/v Jedi

Yes, so the G10 is cut out with rounded corners and after cutting, the sharp edges are filed round as well. I use a router with roundover bit for that.

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.