chainplate backing plates - G10, how thick?

[stantale]

Hi All,

we've got 1/4" standing rigging with 1/4" stainless chainplates. Planning on using FR-4/G10 as backing plates epoxied to hull, with big washers for the 1/2" bolts.

Wondering what thickness I should use. Same 1/4" or should I size up to 3/8"?

Any advice appreciated!

[tommays]

i do not understand how you intend to use the material ?

what are you bolting the chainplate to Bulkhead or ?

[stantale]

chainplate is 316L stainless, hull is fiberglass, backing plate is FR-4/G-10.

Backing plates will be epoxied to hull for the forward/aft lowers, and at the bulkhead (so will used an L-shaped piece of G10) to throughbolt on the bulkhead.

[mitiempo]

If you are bolting chainplates to the hull and the chainplates were not mounted this way before you have to beef up the hull in an area much larger than the chainplates themselves.

I don't have the info handy but Dave Gerr has it in his book "The Elements of Boat Strength"

[stantale]

thanks for the answers - the existing chainplates were glassed into the hull (hence replacing them since they can't be inspected) so it is plenty strong.

The old ones aren't corroded and look reasonable at every point I dug in to inspect them - but how good can they be after 40 years...

In any case I still need backing plates on the inside. Choices are aluminum/steel/G10 and it seems to me like G10 is a great material - less metal issues, and I can epoxy/glass it to the hull for more integral strength. A lot of people seem to be using it to back chainplates.

I'm just not sure of the thickness I should use. It's not mentioned as much in sailboat repair literature since it's a newer material.

[mitiempo]

If the hull is thicker where the chainplates are going, since they were there before, I think I would use 1/2" and make it larger than the chainplate by maybe an inch on all sides. The bolts will be in sheer and the extra thickness helps. I would taper the edges as well.

[stantale]

1/2" !? Have you seen the price of G10 ;-)

That sounds right - and I do have them 4" wide for 1.5" wide chainplates.

When you say edge tapered, you mean the outside, correct? So it doesn't slice up fingers and whatever else is in the cupboard. I was planning to do so + glass them in so they really shouldn't budge.

Thanks for the help, as always!

[mitiempo]

That should work fine. By taper I mean the edges should be thinner than the 1/2" to avoid a hard spot - say 1/4" at the edges.

[stantale]

Thank you mitiempo, that is a great suggestion - have been doing so to taper filled thru-hulls bit it didn't occur to me on the backing plates.

I think I'm all set - thank you for the great advice, as always!