Backing plate material

[zoidberg]

G10, make the thickness about the same as the fastener diameter.
It lasts forever and does a better job of spreading the load then plywood, and doesn't corrode / oxidise like steel or aluminium.

I like to epoxy bond it in place and then drill / tap it. Tapping it isn't necessary, but it makes single headedly fitting the deck hardware a doddle. (You still need a nut and penny washer on the back, it just means you don't need someone on deck to hold the screwdriver)
Use a carbide jigsaw blade to cut it, it will blunt a normal steel blade within seconds.

The only real downside is that its quite expensive stuff.

Thank for that, Ceirwan.

I guess I'm fortunate in having 'rescued' half a dozen sheets/plates of 13mm stuff that 'walks, talks and quacks' like G10. I've already used pieces to 'beef up' under my foredeck where I've fitted a hefty 12mm U-bolt for an inner forestay and also where I've fitted a Selden Bow Ring for a bowsprit.
I'll use more to reinforce, as mentioned, where I'll mount fittings for a JSD.

Thanks for the suggestion about 'tapping' threads - that WILL save a fair bit of cussing! I'll find an engineer ( old school ) who can advise re drill/tap sizes for the specific bolts I have.

Also, re the 'carbide jigsaw blade'. In my ignorance I've used a bandsaw, and have blunted TWO blades - so YES.

 

[Bouba]

As an alternative to tapping a thread....is welding a captive nut....here’s one I made earlier...

 

[zoidberg]

Thanks, Bouba!
I don't have welding kit, so I simply used a blob or two of JBWeld, as in #15 although that's not shown.

We're 'on the same page'.

 

[Snowgoose-1]

My Sadler 34 has no backing plates for the genoa winches that were originally Lewmar 40 non-ST. We intended to upgrade to Lewmar 43 ST but at the chandlery we found a pair of Gibb 50s, very reasonable as they had just gone out of business. They have been extensively used for well over 30 years with absolutely no evidence that they need any backing plates whatsoever. The layup is quite thick here and loading is in shear, needing no reinforcement.

I had a 1970's grp folk boat clone. There were no backing plates for anything , just penny washers. The areas just seemed to have beefed up grp.