What is the prefered metal or material for backing plates. Some of mine are plexiglass and some are wood. As this is a new boat for me I am trying to upgrade or look for possible trouble spots that I should fix/replace before they break.
BACKING PLATES
- Thread starter DREW6713
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If your P26 is like mine or like my current 10M the OEM backing plates are fiberglass. They made them from scraps. They are a bit uneven and often are made from interior liner scraps which was made from chopper gun. So the OEM backing plates tend to get deformed. Good idea to replace them. I would go with 1/8" stainless steel (maybe 3/32) or fiberglass. I used fiberglass that comes in sheets from McMaster Carr to make some backing plates for some padeyes I mounted on the foredeck of my 10M. See a photo here: dan.pfeiffer.net/10m/foredeck_padeyes.htm Go to mcmaster.com and put in part number 8537K25 for a suitable panel. 12x12" and 1/4" thick. This glass is much sturdier than the glass Pearson used for the backing plates. But I think I would still prefer SS given the option. But it's harder to work with and the fiberglass I used in the example above is a big upgrade form the OEM. Also note the fender washers. You should also de-core around fastener holes and fill with epoxy and, if the underside surface where the backing plate goes is un-even, I would set the backing plate in a mash of epoxy/filler (e.g. West System 406) to get a good mating surface. See some more details on methods here: dan.pfeiffer.net/boat/hdwrinst.htm Dan Pfeiffer
Plexiglass - Perplexing
Drew, I don't doubt your word, I haven't owned a Pearson, but I've sailed them, and they are well-built. Plexiglass is a strange material for 'backing plates'. stainless, or even aluminum, if it is against the glass, is normal, or even good sized washers. Wood filler, like a tapered hull-shaped piece to 'fill' the space for a thru-hull. even ply beneath a windlass, with heafty stainless plates to suck up against the ply whence the stainless bolts are tightend up to nylocks or doubled lock nuts underneath. The Idea is OVERKILL, you cannot make it too strong, and you may one day use your jib winch to pull yoursel out of the mud, lotta physics involved thar...
Drew, I don't doubt your word, I haven't owned a Pearson, but I've sailed them, and they are well-built. Plexiglass is a strange material for 'backing plates'. stainless, or even aluminum, if it is against the glass, is normal, or even good sized washers. Wood filler, like a tapered hull-shaped piece to 'fill' the space for a thru-hull. even ply beneath a windlass, with heafty stainless plates to suck up against the ply whence the stainless bolts are tightend up to nylocks or doubled lock nuts underneath. The Idea is OVERKILL, you cannot make it too strong, and you may one day use your jib winch to pull yoursel out of the mud, lotta physics involved thar...
Dan
Dan, Good on ya mate, glad you chimed in, I'm learning here too. Fiberglass is glass fibers 'soaked' permeated with polyester resin (cheaper than epoxy), and pretty bendy. Not the ideal material for 'backing-[plates', but who can argue with success. Wonder how many mates have hangovers today? I'm okay, but only a dozen beers or so last night...
Dan, Good on ya mate, glad you chimed in, I'm learning here too. Fiberglass is glass fibers 'soaked' permeated with polyester resin (cheaper than epoxy), and pretty bendy. Not the ideal material for 'backing-[plates', but who can argue with success. Wonder how many mates have hangovers today? I'm okay, but only a dozen beers or so last night...
Backing Plate Material
Like I said, I prefer SS but the fiberglass I mentioned from McMaster Carr is a significant upgrade over the OEM backing plates and quite serviceable in this application. And it is basically the same structure as the skins of the deck (though not of woven roving as the outer skin of the deck) so it is no more flexible than that? I would certainly prefer it over plywood. Much stronger and stiffer. The McMaster glass is an extruded product with very good control on glass content and thickness and while I don't expect it is as strong as vacuum bagged biax glass it is likely better than a typical hand lay-up. Dan Pfeiffer
Like I said, I prefer SS but the fiberglass I mentioned from McMaster Carr is a significant upgrade over the OEM backing plates and quite serviceable in this application. And it is basically the same structure as the skins of the deck (though not of woven roving as the outer skin of the deck) so it is no more flexible than that? I would certainly prefer it over plywood. Much stronger and stiffer. The McMaster glass is an extruded product with very good control on glass content and thickness and while I don't expect it is as strong as vacuum bagged biax glass it is likely better than a typical hand lay-up. Dan Pfeiffer
Everyone has discussed fiberglass or plexiglass for backing plates. Ive always used 1/2 inch exterior grad plywood coated with epoxy resin worked fine for me on winches, cleats ect. No problems or failures over the last 40 years Bob Fox 1975 P26w # 76 whitecap Marblehead
size matters?
Capt Ron, it looked like plexiglass but now I believe it was as Dan said some kind of left over scraps. It appears as though I should make the new backing plates twice the size of the item I'm mounting? The boat has 2 harken self tailing winches held on by stainless washers and that makes me a bit uneasy.
Capt Ron, it looked like plexiglass but now I believe it was as Dan said some kind of left over scraps. It appears as though I should make the new backing plates twice the size of the item I'm mounting? The boat has 2 harken self tailing winches held on by stainless washers and that makes me a bit uneasy.
Dan any relation to Michelle?
You likely get that allatime, what a dish! Most decks are cored, with end-cut balsa. but not all. Take apiece of glass, Polyester (98% of all sailboats are made of, or epoxy, doesn't matter) now as an experiment, bend it. Now, take a piece of stainless... Just called a friend and yep, he did have FRP 'backing-plates' but he changed to stainless for ocean work.
You likely get that allatime, what a dish! Most decks are cored, with end-cut balsa. but not all. Take apiece of glass, Polyester (98% of all sailboats are made of, or epoxy, doesn't matter) now as an experiment, bend it. Now, take a piece of stainless... Just called a friend and yep, he did have FRP 'backing-plates' but he changed to stainless for ocean work.
right angles
The whole purpose of the backing plates is to distribute the loads over a wider section of the mounting surface. Much easier to pull a couple of washers through a fiberglass skin then it is to pull a thick metal plate through. If the deck is cored then it isn't posible to tighten the fasteners without crushing the core. From one side(it doesn't matter which)bore out a section about 4 times the diameter of the fastener and fill it with epoxy putty. then drill for the fasteners and a thick metal or hard wood backing plate. Don't forget the bedding compound.
The whole purpose of the backing plates is to distribute the loads over a wider section of the mounting surface. Much easier to pull a couple of washers through a fiberglass skin then it is to pull a thick metal plate through. If the deck is cored then it isn't posible to tighten the fasteners without crushing the core. From one side(it doesn't matter which)bore out a section about 4 times the diameter of the fastener and fill it with epoxy putty. then drill for the fasteners and a thick metal or hard wood backing plate. Don't forget the bedding compound.
A few points
Few things here. I may or may not be under a restraining order when it comes to discussing Michelle. I am not allowed to say. Take a piece of the 1/4" FRP plate I referenced above (Mcmaster Carr # 8537K25) and try to bend it. If you can, quit your day job and join the circus as a strong man. No it is not as strong as SS but it is a lot stronger than the plates that were used by Pearson. I would prefer SS but these will serve well as hardware backing plates, better than 1/2 plywood which you would also be hard pressed to destroy bare handed. I would only use epoxy in any work like this. All the bonding to the original surfaces will be secondary bonding. That means mechanically glued, no chemical bonding (crosslink) as with a primary lay-up. Polyester is pretty good in primary bonding, epoxy is a bit better. But for secondary epoxy is a lot better. Two to three times stronger in secondary bonding I think. I would need to check that and there are variables like adhesive fillers to consider. But it is a lot stronger. And I find it easier to work with (in my experience anyway) and much less nasty fuming. The instructions and guide materials from the epoxy makers (West System, MAS, etc) are excellent. All well thought-out systems. Epoxy's weakness as compared to polyester is UV vulnerability. It needs to be protected from sunlight. Painting is fine. Fortunately for this hole filling job sunlight will not be an issue. As for core replacement with epoxy, it does matter which side you over drill to 4X the bolt diameter. Take a look at the deck lay-up. Outer skin is 3/16 to 1/4" lay-up of mat+woven roving. Then 3/8 to 1/2" balsa depending on location (and it tapers at outboard edge of deck), then the inner skin which was done by chopper gun. That's right, Pearson used a chopper gun to do the inner deck skin. The outer skin is a whole heck of a lot stronger than inner so if you're going to cut one away for back fill make it the inner. But I wouldn't do it that way. You don't need to greatly enlarge the holes. Go to 3/8" or so for a 1/4" fastener (as with stanchion bases). I would do it by digging out the balsa by back-cutting from the hole with a 1/8" allen key chucked in a variable speed cordless drill. Get three of them and cut the short end to a chisel shape of three different lengths. Start with short (1/4") and work up to long (about 3/4") and ream out the balsa. Use the clutch on the dill to leep from bending the allen keys. Use a vacuum to suck out the chips. Then tape over the holes below (electric tape will do nicely) and pour in thickened epoxy (I use West 406 filler for this). Thick enough so it can still be poured. Use a syringe if you like to fill in the holes. Stir it in with a tooth pick to get bubbles out. When it's set drill through the epoxy for the fasteners. Chamfer the top of the hole a bit (1/16" or so) to retain sealant and seal with polysulfide (e.g. BoatLife Life Caulk). For some installations I drill and tap the mounting holes and apply sealer to the threads. This give a really good seal. Still use backing plates and backing nuts/washers. See details with illustrations of this method here: dan.pfeiffer.net/boat/hdwrinst.htm And see a photo of my de-coring tools here: dan.pfeiffer.net/boat/de-coring_tools.jpg Copy those lines to a browser address line to see the pages. Dan Pfeiffer
Few things here. I may or may not be under a restraining order when it comes to discussing Michelle. I am not allowed to say. Take a piece of the 1/4" FRP plate I referenced above (Mcmaster Carr # 8537K25) and try to bend it. If you can, quit your day job and join the circus as a strong man. No it is not as strong as SS but it is a lot stronger than the plates that were used by Pearson. I would prefer SS but these will serve well as hardware backing plates, better than 1/2 plywood which you would also be hard pressed to destroy bare handed. I would only use epoxy in any work like this. All the bonding to the original surfaces will be secondary bonding. That means mechanically glued, no chemical bonding (crosslink) as with a primary lay-up. Polyester is pretty good in primary bonding, epoxy is a bit better. But for secondary epoxy is a lot better. Two to three times stronger in secondary bonding I think. I would need to check that and there are variables like adhesive fillers to consider. But it is a lot stronger. And I find it easier to work with (in my experience anyway) and much less nasty fuming. The instructions and guide materials from the epoxy makers (West System, MAS, etc) are excellent. All well thought-out systems. Epoxy's weakness as compared to polyester is UV vulnerability. It needs to be protected from sunlight. Painting is fine. Fortunately for this hole filling job sunlight will not be an issue. As for core replacement with epoxy, it does matter which side you over drill to 4X the bolt diameter. Take a look at the deck lay-up. Outer skin is 3/16 to 1/4" lay-up of mat+woven roving. Then 3/8 to 1/2" balsa depending on location (and it tapers at outboard edge of deck), then the inner skin which was done by chopper gun. That's right, Pearson used a chopper gun to do the inner deck skin. The outer skin is a whole heck of a lot stronger than inner so if you're going to cut one away for back fill make it the inner. But I wouldn't do it that way. You don't need to greatly enlarge the holes. Go to 3/8" or so for a 1/4" fastener (as with stanchion bases). I would do it by digging out the balsa by back-cutting from the hole with a 1/8" allen key chucked in a variable speed cordless drill. Get three of them and cut the short end to a chisel shape of three different lengths. Start with short (1/4") and work up to long (about 3/4") and ream out the balsa. Use the clutch on the dill to leep from bending the allen keys. Use a vacuum to suck out the chips. Then tape over the holes below (electric tape will do nicely) and pour in thickened epoxy (I use West 406 filler for this). Thick enough so it can still be poured. Use a syringe if you like to fill in the holes. Stir it in with a tooth pick to get bubbles out. When it's set drill through the epoxy for the fasteners. Chamfer the top of the hole a bit (1/16" or so) to retain sealant and seal with polysulfide (e.g. BoatLife Life Caulk). For some installations I drill and tap the mounting holes and apply sealer to the threads. This give a really good seal. Still use backing plates and backing nuts/washers. See details with illustrations of this method here: dan.pfeiffer.net/boat/hdwrinst.htm And see a photo of my de-coring tools here: dan.pfeiffer.net/boat/de-coring_tools.jpg Copy those lines to a browser address line to see the pages. Dan Pfeiffer
Another Choice
On my P33 I use maintenance free StarBoard as backing material. When visible it can be decoratively shaped and routed to match trim. Depending upon what I have mounted, a thickness' of 1/2" to 1" with SS trim or fender washers have held without any problems. With a little effort, StarBoard can be found very inexpensively as scrap material.
On my P33 I use maintenance free StarBoard as backing material. When visible it can be decoratively shaped and routed to match trim. Depending upon what I have mounted, a thickness' of 1/2" to 1" with SS trim or fender washers have held without any problems. With a little effort, StarBoard can be found very inexpensively as scrap material.
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