Would A Hardwood Be An Acceptable Backing Plate - SailNet Community
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post #1 of 23 Old 02-27-2011 Thread Starter
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Would A Hardwood Be An Acceptable Backing Plate

I will be installing three pad eyes in my cockpit as attachment points for tethers. I have some 1X6 boards of maple, red oak, and birch in my garage. Could one of these hardwoods act as an acceptable backing plate?

An add on question: when I drill through the side of the fiberglass lazarette how can I avoid any spider cracks or chips in the surrounding fibergalsss?

Thanks for any advise.
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post #2 of 23 Old 02-27-2011
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No, regular lumber isn't really a suitable backing plate because they can split under a load. Plywood is often used because it won't split, but it does rot, and generally is recommended that it be epoxy saturated to prevent rotting.

IMHO, the best material for backing plates is Garolite G10 fiberglass, which you can get from a variety of sources.

The next best alternative is plain fiberglass plates, which you can make up yourself.

Then aluminum or stainless steel--aluminum has issues with galvanic corrosion with stainless steel fasteners and stainless steel is very hard to work.

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post #3 of 23 Old 02-28-2011
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King Starboard is a plastic material often used for backing plates. It's a bit flexible, so you need to make the backer slight larger than you would if it were metal. Plywood works well, but it needs to be a little on the thick side, so in some applications it's better to go with metal. Also, if you use plywood, make sure to seal it with epoxy (preferably a penetrating or thinned epoxy) to keep it from rotting.

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Starboard is not a structural material and should not be used for backing plates. It isn't designed for it and it is pretty expensive and needs to be far thicker than more suitable materials like Garolite G10, which will work quite well at 3/8" thick for 99.9% of purposes.

Remember to round the corners of the backing plates rather generously to prevent stress risers and hard edges from causing the fiberglass to fatigue. Bed the backing plates in thickened epoxy to ensure that the loads are spread evenly against the deck's underside.

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post #5 of 23 Old 02-28-2011
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Historically, white oak was typically used for backing plates and still makes a good backing plate. My current favorite backing plates are 5/16" aluminum plate or else build up epoxy and cloth and they use that with a fender washer. Hardwoods like maple, red oak, and birch are more rot prone than white oak and so would not work as well.

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post #6 of 23 Old 02-28-2011
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For what its worth:

I have a friend who buys Ikea cutting boards and cuts them to fit to make backing plates.



No rust, easy to work with, tuff as nails . . .

Just a thought.

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post #7 of 23 Old 02-28-2011
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Neither Red oak, birch nor maple are sufficiently rot resistant for this use.
white oak is better but tends to check. For north american hardwoods, Black locust would be a better bet.

I've had very good luck with Ipe or purpleheart, with ipe being perferred. Honduras Mahogany is okay as well but not as strong and should be coated.

Never use plywood unless it's pretty much soaked in epoxy- Ply is like a sponge for water ingress when the edges are uncoated.

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post #8 of 23 Old 02-28-2011
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I would try these guys for garolite and similar materials: McMaster-Carr

their ordering process is a little less-than-consumer friendly, but you do get your stuff on time.
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Quote:
Originally Posted by sailingdog View Post
Starboard is not a structural material and should not be used for backing plates. It isn't designed for it and it is pretty expensive and needs to be far thicker than more suitable materials...
I've seen King Starboard used for backers on several boats, and I've never seen it fail or need to be replaced -- in fact, I've never heard any complaints by those who have used it. I've used it in a couple of instances, and it seems to work fine. IMHO backers that give just a bit aren't necessarily a bad thing. The backer should distribute the load over a wider area than would large washers, but the ability to absorb "shock" load by flexing/compressing a tad can also be quite advantageous.

Getting back to regular lumber as backing plates, I have seen a couple of cases where it has split. But those were both Red Oak, an open grain wood which really shouldn't be used for anything structural on a boat. Also, as I recall, at least one of those instances (possibly both) was a piece of quarter-sawn lumber (where the grain goes across the thickness of the board). Plain-sawn lumber (where the grain goes across the width of the board, or forms broad semi-circles) is more appropriate for such uses. As with any material which might rot, I would treat regular wood with a couple of coats of thinned epoxy before installing it.

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post #10 of 23 Old 02-28-2011
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Quote:
Originally Posted by rikhall View Post
For what its worth:

I have a friend who buys Ikea cutting boards and cuts them to fit to make backing plates.



No rust, easy to work with, tuff as nails . . .

Just a thought.

Rik
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