Ply or grp for cleat backing plates

[Hardhead]

Originally Posted by s/v Jedi

How do you know it works great? Did you have a storm where your neighbors got their cleats ripped out the deck while you had no damage?

Or do you mean that they fit when you installed them?

Probably means they work great, and he's never had a problem with them despite all the forces they've been subjected to. I use that term all the time.

[s/v Jedi]

Originally Posted by Hardhead

Probably means they work great, and he's never had a problem with them despite all the forces they've been subjected to. I use that term all the time.

If you add backing plates while your neighbors didn't and all are just fine without ripped out cleats then you can't state that the backup plates work great. You can hope that they will work great when your neighbors cleats get ripped out but only know for sure when that time comes

I have some stern cleats with 3/8" King Starboard backing plates underneath a 1-5/8" thick deck that has a 1" balsa core. We had a 55kt squall come through and I ripped the cleats out of the dock (1" diameter bolts through 6" thick beams) while my cleats were fine. Do my backing plates work great? I don't know, I never tried the same test without them

[billnz]

those plastic cutting boards work just fine , big washers a must.

[Uncle Bob]

Originally Posted by billnz

those plastic cutting boards work just fine , big washers a must.

Emphasis on the big, both dimensions.

[guyrj33]

I made 1/2" topping plates and 1/4" backing plates for my stanchions using this material from McMaster-Carr. Less expensive than G-10.
https://www.mcmaster.com/fiberglass-sheets

Structural FRP Fiberglass Sheets, Bars, and Strips

An alternative to wood in structural applications, these FRP fiberglass sheets, bars, and strips are strong and lightweight. They're made of fiberglass-reinforced polyester.

Sheets
Color: Green
Max. Temperature: 140° F
Tensile Strength: 7,000-40,000 psi (Good)
Impact Strength: 4-30 ft.-lbs./in. (Excellent)
Hardness: Barcol 40 (Hard)
For Use Outdoors: No
12" × 12"
24" × 24"
48" × 48"
48" × 96"
Thick. Thick. Tolerance Flatness
Tolerance Each Each Each Each
1/8" -0.025" to 0.025" 0.008" per in. 8537K23 $10.17 8537K43 $42.49 8537K33 $110.12 8537K13 $202.24
3/16" -0.028" to 0.028" 0.008" per in. 8537K24 12.59 8537K44 45.82 8537K34 164.71 8537K14 288.00
1/4" -0.037" to 0.037" 0.008" per in. 8537K25 16.20 8537K45 68.71 8537K35 200.39 8537K15 348.44
3/8" -0.056" to 0.056" 0.008" per in. 8537K27 28.79 8537K47 107.72 8537K37 326.51 8537K17 567.85
1/2" -0.075" to 0.075" 0.008" per in. 8537K26 32.49 8537K46 125.15 8537K36 382.72 8537K16 665.71

[thinwater]

Originally Posted by guyrj33

I made 1/2" topping plates and 1/4" backing plates for my stanchions using this material from McMaster-Carr. Less expensive than G-10.
https://www.mcmaster.com/fiberglass-sheets

Structural FRP Fiberglass Sheets, Bars, and Strips

An alternative to wood in structural applications, these FRP fiberglass sheets, bars, and strips are strong and lightweight. They're made of fiberglass-reinforced polyester.

Sheets
Color: Green
Max. Temperature: 140° F
Tensile Strength: 7,000-40,000 psi (Good)
Impact Strength: 4-30 ft.-lbs./in. (Excellent)
Hardness: Barcol 40 (Hard)
For Use Outdoors: No
12" × 12"
24" × 24"
48" × 48"
48" × 96"
Thick. Thick. Tolerance Flatness
Tolerance Each Each Each Each
1/8" -0.025" to 0.025" 0.008" per in. 8537K23 $10.17 8537K43 $42.49 8537K33 $110.12 8537K13 $202.24
3/16" -0.028" to 0.028" 0.008" per in. 8537K24 12.59 8537K44 45.82 8537K34 164.71 8537K14 288.00
1/4" -0.037" to 0.037" 0.008" per in. 8537K25 16.20 8537K45 68.71 8537K35 200.39 8537K15 348.44
3/8" -0.056" to 0.056" 0.008" per in. 8537K27 28.79 8537K47 107.72 8537K37 326.51 8537K17 567.85
1/2" -0.075" to 0.075" 0.008" per in. 8537K26 32.49 8537K46 125.15 8537K36 382.72 8537K16 665.71

^^ What he said. G10 is great if you need to tap threads or machine it, but otherwise, the need for it is forum legend. I have lab tested backing plates of many materials, and the structural FRP described above is absolutely as effective for less than 1/2 the price.



Basically, you are buying stiffness more than strength. You are transferring the load to the surrounding structure. If the FRP is thick enough not to flex, it will be WAY stronger than needed (this is NOT true with wood).


As long as the thickness = fastener dia and the plate is at least 5x (10x is better) fastener diameter across with min 1" radius corners, you're good. I'd feel silly using more, and I've broken a lot of plates, of a lot o materials, in testing.