Ply or grp for cleat backing plates

[Pugcat]

Hi, the backing plates for my cleats are currently plywood which is then glassed over underneath, making it totally encased. Over the years some of the bolts have leaked and the ply has gone soft around these bolts.

Getting them off is going to be a pig of a job so am considering what to put back. I was thinking of buying fibreglass sheet and maybe sticking a few layers together then to the hull underside but is there any advantage to using ply? I mean, it’s not as if the builders were short of fibreglass supplies when they built the boat so why go to the trouble of using ply at all, particularly as they then glassed over it anyway. Is using straight GRP a bad idea? Thanks

[zboss]

http://www.cruisersforum.com/forums/...es-187469.html

[Spot]

We have 6.35mm(1/4") G10/FR4 board at work. The scrap is lovely for stuff like this...

[billknny]

Originally Posted by Pugcat

Hi, the backing plates for my cleats are currently plywood which is then glassed over underneath, making it totally encased. Over the years some of the bolts have leaked and the ply has gone soft around these bolts.

Getting them off is going to be a pig of a job so am considering what to put back. I was thinking of buying fibreglass sheet and maybe sticking a few layers together then to the hull underside but is there any advantage to using ply? I mean, it’s not as if the builders were short of fibreglass supplies when they built the boat so why go to the trouble of using ply at all, particularly as they then glassed over it anyway. Is using straight GRP a bad idea? Thanks

Don't use fiberglass sheets, especially in a stack. They will be soft and flexible, and can crush when bolts are tightened down hard.

The BEST material by far for backing plates is called G10. It is a VERY hard glass epoxy matrix. It will not crush or rot like plywood, not corrode like metal. 1/2" thick should be about right.

It's not the cheapest stuff you can use, but you don't need a lot either.

[billknny]

It's unanimous! When does that EVER happen here?

[s/v Jedi]

Originally Posted by billknny

It's unanimous! When does that EVER happen here?

but we can still add to it :-)

-> round the corners and taper the edges of the G10 backing plates (grind them sharp from the underside) to avoid hard spots

-> glue them with West System epoxy, filled with microfibers to a peanut butter consistency, then put a layer of fiberglass cloth and a layer of pull-ply on, wetted out with un-thickened West System.

-> if there is a plywood or balsa core, remove that around the bolt holes and cast epoxy thickened with high density filler to replace it (prevent crushing the core and prevent water getting into the core)

[Thumbs Up]

How long did they last that way? Do this and it will be fine for the next 20 years or so: You will have to grind it all flat from underneath which will be a nasty job but quick. G-10 , can you get it where you are? Get some treated plywood scraps, (it will have a greenish tinge, find the thickest stainless steel washers that you can get, make sure that the wood is dry, over drill the holes a little, mask everything off really good, install the cleat The bolts, and the plywood backing plate all at once, smear epoxy mixed with cabosil all over everything, assemble and tighten the bolts, remove the tape. Don't forget to buy rubber gloves. As for the advantage, It is lighter and cheaper

[laika]

Originally Posted by s/v Jedi

but we can still add to it :-)

-> round the corners and taper the edges of the G10 backing plates (grind them sharp from the underside) to avoid hard spots

-> glue them with West System epoxy, filled with microfibers to a peanut butter consistency, then put a layer of fiberglass cloth and a layer of pull-ply on, wetted out with un-thickened West System.

-> if there is a plywood or balsa core, remove that around the bolt holes and cast epoxy thickened with high density filler to replace it (prevent crushing the core and prevent water getting into the core)

Order it from McMaster Carr if you can't source it locally. It's not expensive for the amount you need.

[Singularity]

Using GRP only is not a bad idea, but I would drill-fill (milled fiber)-drill.

If given the options of:
1) 1/4" G10 6in x 6in $15.85
2) 1/2" G10 6in x 6in $31.70
3) 1/2" hand layed-up fiberglass/epoxy stack, holes oversized drilled then filled with epoxy/milled fiber slurry then final hole drilled ~+/-$10

I'd choose #3 all day unless someone gifted me thick G10. With the cost savings make the plates a little larger. If you can compress a 1/2" column of hardened epoxy/milled fiber then you are doing something wrong to your bolt threads.

Let's not lose perspective and develop groupthink such that we insist that the only way to do things is the most expensive way. Stacked glass is far superior to ply and ply works (until it gets wet etc).

[RaymondR]

Alloy flat bar. Cheap and easy and you don't need to glass it in.

[Fore and Aft]

How about the bottom of a plastic margarine container or some other disposable rectangular/circular plastic container? Whenever I had left over resin I would pour it into a plastic conatiner along with some fiberglass matt and when its cured you have a nicely moulded fiberglass backing pad that can be as thick or thin as you like. Another firm I worked at had a peice of fiberglass that was always being laid up with leftover resin and fiberglass. When it got to around half a meter square a new peice was then started again. That fiberglass sheet was always getting used for backing blocks.
Cheers

[Chotu]

Aluminum plates also work. I have marine ply and it's working fine too.

[ausnp84]

I’m about to fit midship cleats and will be going down the 1/4 G10 route. Seems like solid stuff and has the advantage of not rotting anytime soon!

N

[Chotu]

Originally Posted by Chotu

Aluminum plates also work. I have marine ply and it's working fine too.

Expanding on this.

The idea is you want something that will take the compression loads of the bolts and huge washers. Your backing plate is essentially an even bigger washer spreading the load out onto a greater area of the deck.

It just has to be good with compression forces. Should not be easily crushed.

It doesn't really matter if it's water resistant because you should be installing your cleats better than that.

I used untreated marine plywood 5 years ago. Not a drop of water comes in. Ever. So it's not an issue.

Use butyl tape under the cleat and tighten it down into that. You'll never have a drip.

[Bill O]

Another vote for aluminum plate. Never used G10 but seems somewhat expensive compared to the 1/4" plating I can pick up as inexpensive scrap.

Don't know how long G10 has been around, but the aluminum plating has worked well for decades as backing plates for cleats, sheeting tracks, etc.


Bill O.