Backing plates

[SVCetacea]

My 30 foot sailboat doesn't have backing plates for any deck hardware or the backstays, just washers.
Needless to say, I will be adding them. But what material? I run a plasma cutter in a steel shop, meaning I can custom cut plates and get the steel for free, but we don't carry stainless steel. Is it ok to use some regular high strength steel (not mild steel), or is stainless the only way to go?
What would be a good thickness to use?

[sailingdog]

I wouldn't use plain steel. If you can't get 3/16-1/4" 316 stainless steel, use 1/4-5/16" aluminum instead. If you use regular steel, you'll be cleaning up a lot of rust stains... pretty much guaranteed.

[rhaley]

My personal preference is prefab fiberglass that can be had from places like McMaster-Carr. No rust or rot, and it can be cut and drilled with regular tools (although it is tough on the blades and bits). I use anywhere from 1/4" to 1/2" depending on the situation.

[majorm]

SD- I am also adding backing plates in several places. Is there a big difference between aluminum and stainless? I am able to get 1/4" stainless.

[USCGRET1990]

Originally Posted by majorm

SD- I am also adding backing plates in several places. Is there a big difference between aluminum and stainless? I am able to get 1/4" stainless.

Aluminum is a heck of alot easier to cut and drill for sure!

[majorm]

Let me clarify a little. I would prefer using stainless steel, but am being told that aluminum is sufficient to do the job. I would rather spend what is necessary to do the best job, unless it really doesn't make that much difference.

[lbdavis]

As posted on a previous thread, Ipa is a cheap and excellent alternative. To call it hard wood is understating things. Your boat will be gone before this stuff rots. Seriously. Ask around at good lumber yards or flooring places, it's pronounced EE-pay. It's sold as decking (1"X4" or 1"X6") and is a lot easier to work with than metal, though it's not much easier to drill through.

The dust that comes out of this stuff is an irritant and I would suggest covering skin and eyes as much as possible if you are planing on milling a lot of this stuff.

[kananumpua]

Majorm,

SS has a modulus that is far supperior to that of regular aluminum alloys. However, on most of the race boats I have been on, aluminum has been used. And these boats are put under some serious loads. I believe aluminum is sufficient in its strength and I do not believe it would fail or plasticaly deform if the plate is oversized properly.

[gc1111]

A very experienced and knowledgable marine machinist (he has built one-off stuff for Americas Cup boats) recommended aluminum over stainless. His reasoning was stiffness (you use thicker Al) which does a better job of spreading the load over the comparatively flexible fiberglass which is being backed.

[RXBOT]

Must be nice haveing access to plasma cutter. Surprised you don't have stainless there as thats were plasma cutters really shine. However I would prefer aluminum of appropiate size because of ease of machineing with ordinary tooling. Can't you purchase material through your employer for your own use.