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Boat Forum / Building / December 2004backing plates
Hi all, I want to put on backing plates for all the stuff attached to the transom (exhaust ports, swim platform, steering arms etc). Through continually snugging them, the previous owner has burried a couple of nuts through the glass! I am really new to all this but the first thing that comes to mind is reaction between two metals. If I use stainless bolts, could I use aluminum for backing plates or maybe I should use something else, or maybe I shouldn't do this at all? Still asking and not able to answer much yet. Thanks, Steve Steve; I would look into the reason you have too keep "snugging them", and there's reason to look at the burried nuts. Sounds like a plywood core that's rotten. Backing plates won't help if the center is soft. Jim > Hi all, > [quoted text clipped - 9 lines] > > Thanks, Steve [moved top-post down below OP] >> Hi all, >> [quoted text clipped - 18 lines] > > Jim This is good advice. But to answer one of the original questions, I don't think there is any problem with corrosion between aluminum backing plates and stainless hardware. For one thing, you will be putting some kind of sealant in the hole, and this sealant will probably end up mostly insulating the aluminum from the stainless. And for another thing, it will take a long time (20 years?) for there to be enough corrosion on a 0.125" backing plate to worry about. --Mac On Sun, 12 Dec 2004 03:54:43 GMT, Jim <Jim@hotmail.com> vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email >I would look into the reason you have too keep "snugging them", and >there's reason to look at the burried nuts. Sounds like a plywood core >that's rotten. Or maybe a bad design that has a foam core with not even "pads" between the glass where there are pressure plates. >Backing plates won't help if the center is soft. Which can apply with foam. Same problem occurs. It's best to have solid "pads" at pressure points, even with backing plates on top. --- Only worry about the things you can control. Then you have stuff all to worry about! Top posting versus bottom posting, let me explain, scroll down: > On Sun, 12 Dec 2004 03:54:43 GMT, Jim <Jim@hotmail.com> vaguely > proposed a theory [quoted text clipped - 17 lines] > > Then you have stuff all to worry about! There, see? You has to scroll down to read what you could have read without moving your cursor and scrolling. I don't know why you said "vaguely > proposed a theory . . ." Saying to check the reason for the loose bolts isn't exactly vague. I know about how today's powerboats are made, and I'll bet he's got some rot in a piece of structural plywood. If that's the case, backing plates will not fix it. Jim On Sun, 12 Dec 2004 18:10:49 GMT, Jim <Jim@hotmail.com> vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email >Top posting versus bottom posting, let me explain, scroll down: > [quoted text clipped - 22 lines] >There, see? You has to scroll down to read what you could have read >without moving your cursor and scrolling. So are you arguing for top or bottome posting? If you had top posted and I had half a brain and had followed the thread, I could have read your reply without having to scroll. And if you had trested the post _correctly_ and removed half the crap from previous posts before you started your bitching, then I would not have had to scroll. >I don't know why you said "vaguely > > proposed a theory . . ." You tell me how to run the Web, then take exception to a stock joke headline? >Saying to check the reason for the loose bolts isn't exactly vague. I >know about how today's powerboats are made, and I'll bet he's got some >rot in a piece of structural plywood. > >If that's the case, backing plates will not fix it. No. And I agreed. Sheeeeesh! Bad hair day guy! --- Only worry about the things you can control. Then you have stuff all to worry about! On Sun, 12 Dec 2004 18:10:49 GMT, Jim <Jim@hotmail.com> vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email _Partial_ understanding of your post. I did not bottom post. You should not have had to scroll to read what I had to say. If you did them sort out your news reader. I extracted what I thought was cogent and interleaved my comments. I do this sometimes, and top post mostly, also often removing a lot of the previous material. I believe that bottom posting is the "correct" way anyway, although I disagree with it. In the end if it's done with a bit of thought it all works. Even if it doesn't work..let it go! >Top posting versus bottom posting, let me explain, scroll down: --- Only worry about the things you can control. Then you have stuff all to worry about! Some people hate top posting. I appreciate it when I don't have to scroll through a bunch of stuff I've already read. Don't know why they want the reply at the bottom. But, we were talking about backing plates. . . > Hi all, > [quoted text clipped - 9 lines] > > Thanks, Steve Backing plates are good, so long as any nearby core material is sealed from moisture ingress with solid pads of epoxy around the bolt holes. There is nothing more destructive over time than water and freezing temperature cycles. There will be very little galvanic action if the metals are not wet with salt water much the time. If they are out of the weather, they will be stucturally fine, especially if they are protected by a good dose of bedding compound, or a coat of primer, paint or wax. While I believe aluminium backing plates would be OK, if I was going to do it from scratch, I would use SS plates, just on spec. Anywhere that does sheet metal will have lots of scraps that will do the job, and the only drawback to SS backing plates is that they are harder to drill by far than is aluminium. At sea, in general, it is always best to use the same metals if they are going to be wet and in electrical contact. Terry K I would make sure the core is very dry and refurbished in some way before any stuff is applied to build up and bed the breaches in the hull. Also different metals in contact in a moist (air) environment, are not the best way to go if you can avoid it. I have a steel boat which is happier with the zincs attached when sitting on its cradle in damp weather. Ask a surveyor who knows steel boats and they will tell you that the humid environment is still going to foster some galvanic action. If your happy with thick plates of a different metal that is your call but you maybe in for a bit of a surprise in the area of under-film corrosion if there is any contact between the metals via the fastening hardware on your glass boat. I have done a bit of corrosion testing with coatings on metals in a lab setting and it is quite impressive to see how insidious nature is when it comes to metals having a "desire" to oxidize in most environments--even before they are coupled. Good luck, Leo > > Hi all, > > [quoted text clipped - 31 lines] > > Terry K Fiberglass backing plates work well with fiberglass. 3/16"or 1/4" solid work well depending on aplication. I make 4x6 ft. sheets w gelcoat and cut with a jig saw. nice finish/no paint Stainless and aluminum will corrode. > Hi all, > [quoted text clipped - 11 lines] > > Thanks, Steve I've been a bit lazier with the same idea and used G-10 fiberglass-epoxy plate from McMaster-Carr (catalog page 3345). It absolutely will not corrode and in greater thicknesses, can be drilled & tapped to save the hassle of nuts in inaccessible locations. > Fiberglass backing plates work well with fiberglass. > 3/16"or 1/4" solid work well depending on aplication. [quoted text clipped - 17 lines] > > > > Thanks, Steve Interesting thought ... but would 1/4" glass would give you anywhere near the same strength as 1/4" aluminum? What sorts of applications have you done and when would you not use them. I'm thinking glass backing plated would be fine where there is no pressure being applied? Steve > Fiberglass backing plates work well with fiberglass. > 3/16"or 1/4" solid work well depending on aplication. [quoted text clipped - 17 lines] > > > > Thanks, Steve > Interesting thought ... but would 1/4" glass would give you anywhere near > the same strength as 1/4" aluminum? What sorts of applications have you done > and when would you not use them. I'm thinking glass backing plated would be > fine where there is no pressure being applied? You could use them in pretty much all places you would use aluminum backing plates. You might make them a little thicker than comparable aluminum thickness (say on the order of the bolt diameter x 0.4 as rule of thumb). I would not use glass backing plates in areas where small dimensions are important. Your last sentence doesn't make sense to me - why have a fitting where no pressure could be applied? Glass (especially G-10) backing plates are SOP on racing yachts.  SignatureEvan Gatehouse you'll have to rewrite my email address to get to me ceilydh AT 3web dot net (fools the spammers) Another plus to G-10 backers just occurred to me- Metal (and g-10) backing plates are hard to taper at their edges, so they're bound to have stress risers at their edges. With G-10, a little feather of bog and another larger layer of glass will taper the stiffness out evenly into the panel. Tidy, too. > > Interesting thought ... but would 1/4" glass would give you anywhere near > > the same strength as 1/4" aluminum? What sorts of applications have you [quoted text clipped - 18 lines] > ceilydh AT 3web dot net > (fools the spammers) G-10 pressure laminates (built correctly)are up to 40% stronger than 6061 tempered aluminum. >> Interesting thought ... but would 1/4" glass would give you anywhere near >> the same strength as 1/4" aluminum? What sorts of applications have you [quoted text clipped - 13 lines] > > Glass (especially G-10) backing plates are SOP on racing yachts. I've been buying G-10 from McMaster-Carr, where 1/4" G-10 is about $23/ft^2. Anybody got a lower-cost source? > G-10 pressure laminates (built correctly)are up to 40% stronger than 6061 > tempered aluminum. [quoted text clipped - 23 lines] > > ceilydh AT 3web dot net > > (fools the spammers) Make them yourself during laminating with scrap amounts of resin/cloth. G-10 is nothing special, just consistent and convenient for a commercial builder but a home builder can do well by just having precut pieces of cloth to use on left over resin. SignatureEvan Gatehouse you'll have to rewrite my email address to get to me ceilydh AT 3web dot net (fools the spammers) I've been buying G-10 from McMaster-Carr, where 1/4" G-10 is about $23/ft^2. Anybody got a lower-cost source? ddinc wrote: G-10 pressure laminates (built correctly)are up to 40% stronger than 6061 tempered aluminum. >> Interesting thought ... but would 1/4" glass would give you anywhere near >> the same strength as 1/4" aluminum? What sorts of applications have you [quoted text clipped - 13 lines] > > Glass (especially G-10) backing plates are SOP on racing yachts. Actually, you can have better strength. It has the same relative stiffness as the fiberglass boat. They will tend to bend together better, and not load the edges as much as a piece of aluminum. The aluminum back pads and the stainless bolts create a corrosion problem as well. I can't tell you how many corroding aluminum backing plates with the paint peeling off I have seen. I have never seen a glass plate do this. > Interesting thought ... but would 1/4" glass would give you anywhere near > the same strength as 1/4" aluminum? What sorts of applications have you [quoted text clipped - 29 lines] >> > >> > Thanks, Steve |
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