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  #11  
Old 02-28-2011
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Use 3/8" garolite aka G10 from Macmaster-Carr. It is bombproof. I use it for backing plates on boats I build.
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Old 02-28-2011
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HDPE is NOT a suitable backing plate material.
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Old 02-28-2011
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Quote:
Originally Posted by SlowButSteady View Post
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 seen it fail to provide the proper support in both a seacock application, which ultimately lead to a leak because NOTHING sticks to it, a stanchion install which lead to a severely crazed deck and a loose stanchion and a set of rope clutches. It is NOT a stiffener or structural product and does not provide point loading distribution across anything other than the diameter of the washers underneath it. As a backing plate by design standards it adds basically nothing to the mix other than a false sense of security.

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Originally Posted by SlowButSteady View Post
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.
And what is your explanation for this theory? The idea behind a backing block is to distribute the loads over a larger area to prevent flexing of the deck or hull. Starboard does not do this unless you can find it in thicknesses over 1". Morris Yachts for example uses aluminum, stainless or G-10 as backing blocks depending upon the item being backed. They never use Starboard and they have lots of it at the factory for other uses..

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Originally Posted by SlowButSteady View Post
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.
Compressing is absolutely not an advantage. This leads to loose fitting bolts, deck flexing, moisture ingress and deck or hull crazing. Contrary to popular misconceptions often times a properly thick fender washer can be more than enough backer depending upon the particular item being backed and the deck construction under it. Hinckley B-40's for example had the hull to deck joint bolted with regular washers but each flange, hull & deck, was over 1/2" thick solid fiberglass with no core. For a stanchion through a cored deck you want to distribute that load but for some item's a backer may not even be necessary.

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Originally Posted by SlowButSteady View Post
Getting back to regular lumber as backing plates, I have seen a couple of cases where it has split.
Me too and it most often splits along the grain right under the nuts but it never should have been installed with the grain oriented that way to begin with. As mentioned IPE, Black Locust and a few others are better choices in a hard wood, but coated marine ply will not crack. Stainless and aluminum of sufficient thickness, G-10, GPO-3 or hand laminated fiberglass are all far superior and will distribute the loads better. Morris, Hinckley, Island Packet and others top quality builders build their vessels with solid glass backers under seacocks and no wood and no plastic lumber.
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  #14  
Old 02-28-2011
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Use 3/8" garolite aka G10 from Macmaster-Carr. It is bombproof. I use it for backing plates on boats I build.

Yep I suspect G-10 and **** roaches will be the only things left after the next nuke war..
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Old 02-28-2011
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Good thread.

Where's a good place to get G-10?

While I'm asking, does anyone know a good place to get stainless backing plates too?

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Brad
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Last edited by Bene505; 02-28-2011 at 01:07 PM.
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Old 02-28-2011
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Quote:
Originally Posted by Maine Sail View Post
And what is your explanation for this theory? The idea behind a backing block is to distribute the loads over a larger area to prevent flexing of the deck or hull.
I was referring to elastic deformation, rather than plastic deformation. A material that deforms a little elastically (i.e., it springs back to its original shape once the load is released) will often absorb a HUGE amount of energy (this is known as "historesis" in materials science). This is also part of the reason why fiberglass has a high strength to weight ratio. It is true that if the material is stressed too much the deformation will be plastic (i.e., it won't spring back) rather than elastic, or it will just plain fail. This is true for ANY material, be it wood, polymer, metal, et cetera. So the "trick" is to make the object in question thick enough to absorb loads in the elastic part of their stress/strain relationship. Too thin, and it will yield and deform plastically, too thick and it will transmit (rather than absorb) the energy. In fact, I imagine that when backers are engineered by real engineers (rather than guys bantering back and forth on sites like this) they intentionally make them thin enough to elastically bend just a bit toward the high end of their design loads, thus absorbing shock loads when necessary.

Personally, I think that stainless or aluminum are probably the best backers (other than for thru-hulls, where epoxy-coated plywood would be my preference). But they're heavier than other materials, harder to drill (particularly stainless), and a PITA to fit to anything but a flat (or nearly flat) surface. I've never used fiberglass as backers, but I see nothing wrong with it. In fact, it may well be better than either wood or King Starboard. I only observed that I've seen Starboard it used on several boats. It's very easy to work with, and I've never seen it fail. I don't think I would use it for applications where the hardware is under long-term stress, however, as it is probably somewhat viscoelastic (i.e., it is elastic in the short-term, but "flows", or deforms plastically, if stressed for a longer period).

Quote:
Originally Posted by Maine Sail View Post
Contrary to popular misconceptions often times a properly thick fender washer can be more than enough backer depending upon the particular item being backed and the deck construction under it. Hinckley B-40's for example had the hull to deck joint bolted with regular washers but each flange, hull & deck, was over 1/2" thick solid fiberglass with no core. For a stanchion through a cored deck you want to distribute that load but for some item's a backer may not even be necessary.
I agree with you there, provided that the underlaying deck/hull is either solid or plywood core. Particularly on some older boats that were build with pretty overly thick scantlings in the first place. My Cal 2-27 had no backers originally, although I've added some (the life-line stanchions are on "the list"). Still, in her 36 year life, none of the original installations have ever failed as far as I can tell (although the aforementioned stanchions have some spider cracks around their bases).

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Originally Posted by Maine Sail View Post
Me too and it most often splits along the grain right under the nuts but it never should have been installed with the grain oriented that way to begin with.
Exactly. In fact, that's the basis for the trick you see in martial arts demos: the boards they break are quarter-sawn, so they split along the grain. I doubt you'll ever see anyone do such a demo with plain-sawn wood, much less plywood.

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Originally Posted by Maine Sail View Post
As mentioned IPE, Black Locust and a few others are better choices in a hard wood, but coated marine ply will not crack.
Just curious, have you ever used Apitong? I bought some to use as a rub-rail on my tender (a project that's still on "the list"). It's supposed to be very rot and wear resistant, although it isn't a particularly pretty wood. The guys at the lumber yard said that they mainly sell it for truck beds and the "fencing" on stake-bed trucks. So, it must be able to handle staying out in the weather.
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  #17  
Old 02-28-2011
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Quote:
Originally Posted by SlowButSteady View Post
Just curious, have you ever used Apitong? I bought some to use as a rub-rail on my tender (a project that's still on "the list"). It's supposed to be very rot and wear resistant, although it isn't a particularly pretty wood. The guys at the lumber yard said that they mainly sell it for truck beds and the "fencing" on stake-bed trucks. So, it must be able to handle staying out in the weather.
I'd say no:

http://www.fpl.fs.fed.us/documnts/Te...carpusspp.html

Tends to check, split or warp. Not something I'd like to "bury and forget about"
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Old 02-28-2011
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I'd say no:

http://www.fpl.fs.fed.us/documnts/Te...carpusspp.html

Tends to check, split or warp. Not something I'd like to "bury and forget about"
It also destroys your shop blades. My buddy used it for some dock work and destroyed expensive blades in just a few rips. While it cost him less per board ft he paid for it in blades. When he researched it he found out the wood has a very high mineral content and that is why it chews up blades so fast. On top of ruining blades it did not hold up nearly as well as the IPE/Ironwood he had previously used.
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  #19  
Old 03-22-2011
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Great thread.

I just went to McMaster-Carr and ordered a 12" x 12" G-10 sheet that's 1/2 inch thick. That ought to make a few good backing plates for upcoming projects.

Hint: when you get to their site, use this exact search term: "Garolite G10 fiberglass". That will get you some pretty pictures, showing you your options. Here's two such pictures.





Regards,
Brad
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Last edited by Bene505; 03-22-2011 at 11:56 AM.
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Old 03-22-2011
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I've used 1/4-inch aluminum plate coated with Epoxy prior to fastening with stainless bolts, nyloc nuts and fender washers. I had to replace all the plywood backing plates on the traveler of my Catalina 27, which were made of plywood and completely rotted. In three years of use there were no signs whatsoever of galvanic activity--none. I would have used 1/4-inch stainless but couldn't find a source at a decent price.

Good Luck,

Gary
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