Quick question about backing plates

[JPS27]

One winter project is to put backing plates where they seem to be needed. There are very few backing plates on my e27. I've read a lot about the materials and creating a uniform bed so the backing plate does its job optimally. Before I go into this winter project can I have some insights into these questions:

1. while maybe not optimal compared to stainless, can I use G10 or aluminum for most plates? I'd like to do the drilling and cutting myself.
2. are there some backing plates that should definitely only be SS?
3. And where I create smooth uniform surfaces for the plates such as below my bow cleats, I have read about supporting the plate against the epoxy with wax paper etc so that it can be removed suggesting that the plates should not be bonded but held in place mechanically. Is that correct?

Thanks!

Jay

 

[Phil MacFarlane]

Hi Jay,

I used G-10 everywhere and I bonded them in place on purpose.

Phil

 

[ignacio]

+1 for G10

I used G10 for backing plates on my mooring cleats, through hulls, windlass, and for my stern chain plate and windvane. My cleat backing plates are held mechanically with through bolts, but the backing plate for the stern chainplate is bonded to the inside of the transom.

 

[e38 owner]

What thickness of G10 would you suggest

I used G10 for backing plates on my mooring cleats, through hulls, windlass, and for my stern chain plate and windvane. My cleat backing plates are held mechanically with through bolts, but the backing plate for the stern chainplate is bonded to the inside of the transom.

What thickness of G10 would you suggest

 

[Shelman]

I think 1/2" should be plenty on our size boat..... but I'm not going to guess at what the lower end of acceptable might be. I have some factory original ones made from aluminum that were 1/4" I think and I would probably not go as thin as that. 3/8" maybe the minimum?
Ahhh there I go guessing at what the lower end of acceptable might be after all.
I would say epoxy in place and remove any core and fill with thickened epoxy while your in there just for good measure.

 

[Loren Beach]

I have used a lot of fiberglass plate, i.e. G10, for backing plates. I would set the plate piece in epoxy mush, permanently. I would use 3/8" thickness at the most. After all, you are going to put ss fender washers under each nut anyway. That stuff is really strong.
But, to start at the beginning, pull out the old bolts and over drill the holes (and see if the coring is dry) and re-fill with thickened epoxy. Then re-drill.

No harm in using some aluminum plate, but in salty air it corrodes and looks ugly.

Older threads about this:
http://www.ericsonyachts.org/infoexchange/showthread.php?5430-Source-for-backing-plates
http://www.ericsonyachts.org/infoexchange/showthread.php?3371-Stanchion-Bracing&referrerid=28
http://www.ericsonyachts.org/infoex...ore-Power-upgrade&highlight=stanchion upgrade

Loren

 

[markvone]

G10 Thickness

I agree with Loren on the thickness 3/8 inch max and 1/4 inch should be fine. The material is very strong in compression (clamping force of the nuts and bolts) and is also very tough and is not brittle. Once you get a piece of it in your hands and drop it on a concrete floor you'll get a good feel for this. For backing plates for all these fittings on a boat deck, the key factor is the added AREA. You are reinforcing the deck (skin/plywood/skin) so that the strong fastener does not pull through or tear across or the weaker deck. A small, but strong nut can pull right through the weaker deck. But add area with a washer and backer and the pull force is spread out over a much greater area. I'm going to use 1/4 inch thick as backing for my new and re-located main traveler under the cockpit seats. The piece is 12 x 15 inches under a 15 long x 1 wide inch track. so it extends 6 inches out from the track sides.

A few notes on cutting G10. A cheap ceramic tile wet saw from Northern Hydraulic or Harbor Freight cuts it like butter with no nasty dust. Drilling small holes with standard bits worked well for me but drilling larger holes > 1/2 inch with hole saws (for thru hull backers) was very hard and wore out the hole saw very quickly.

I usually get my G10 on Ebay in 12 x 12 inch sheets for most projects because it ships for a flat $15 in a USPS Priority Flat Rate box which is 12 x 12 and 3 inches thick so you can get any combo of sheets that add up to 3 inches. You can get bigger pieces on Ebay (like my 12 x 15) but shipping goes up. Plan ahead and get a supply for other small projects. You probably don't need any G10 thicker than 1/2 inch but I got one sheet of 3/4 inch for a specific bilge pump base where I needed to tap the 3/4 side for screws. I used West Gflex thickened epoxy to bond this base to the bilge floor but I usually use Evercoat polyester Kitty Hair mush for my backers.

Mark

 

[JPS27]

cutting G10

Thanks Mark and others. From my internet "research" it looks like I can get away with using a hacksaw and a cobalt drill bit for drilling G10, is that correct? I'm not cutting large pieces so if I can hold off on spending more money on power tools I don't have yet that would be nice.

 

[Nick J]

Hardi Blades

I had a lot of blades for cutting Hardi siding left over after residing my house and they worked great. For cutting small pieces, a jigsaw makes quick work of it.

I think this is what I used:
http://www.amazon.com/Hitachi-72539...452871564&sr=8-1&keywords=hitachi+hardi+blade

 

[markvone]

I drilled with std bits with no issues. The hole saws (which are basically circular saw blades) were many times more difficult.

I had heard about the difficulties of cutting the G10 doing research on the web so I went right to the wet saw and never tried another cutting method. I can also use the saw for tile work but at $68, I really don't need to. I should add that I needed straight cuts only, no curves. Don't think curves will work with the wet saw.

Because wet saws are so cheap and common for tile work, your best bet might be to ask around to borrow one for an hour from a friend. Or check on the cost of a rental.

Here's the one I got. Worked fine.

http://www.harborfreight.com/power-tools/tile-saws/7-in-portable-wet-cut-tile-saw-69231.html

Mark

 

[ignacio]

What thickness of G10 would you suggest

I've mostly used 3/8", but have gone with 1/4" on occasion. The large backing plate for my stern chain plate is a 24"x 24"x 3/8" piece that I bonded in place. Both my wind vane and stern chain plate are through-bolted to it.

Note also that for backing plates, I radius the corners and smooth out the edges with a grinder. Wear a mask if you do that.

 

[Rocinante33]

I see the role of a backing plate to spread the load under the deck. It should keep the bolts & washers from either pulling through or even from crushing the laminate. So really, it only needs to be as strong or slightly stronger than the bottom layer of laminate. 1/4" or even 3/16" G-10 would be much stronger and would do the job, I am sure. I think it would be better to use this smaller thickness G-10 and to use a larger piece (always with rounded corners) to spread the load. Always use fender washers, too, of course.

I don't see a need to bond the backing plate to the deck. One may need to fill if there is a curved surface, though.

 

[tenders]

3/16" G10 is every bit as strong as you'd need for backing plates on any cored area of the deck. The strength of a backing plate is its area, not its thickness.

I've used that thickness for both backing plates and as a replacement top skin when replacing failed core material, and it is WAY stronger than any of the original layers.

The other benefit to G10 is that, unlike aluminum or stainless, it accepts primer and paint very well, and, unlike aluminum, it doesn't corrode. The corners and edges can be a bit sharp, but as previously mentioned are easily rounded and blunted with a grinder.

I wish I'd known about it when I fabricated stainless steel backing plates for all the stanchions on my boat back in 1995. The machine shop had cut the plates for me with a hydraulic chopper - but drilling all the holes took a LOT of cobalt bit resharpening and a lot of back-and-forth to the drill press, which was not located next to the boat!

I buy large sheets from McMaster.com, and small pieces of thicker stuff from a company in Norfolk, VA that comes up regularly on eBay during searches.

 

[JPS27]

Backing plate source

Thanks for the advice. It looks like the Norfolk source is Norva Plastics. I now remember someone saying that Norva is a great source, but back then I was thinking about a different problem so it didn't come to mind. They have a good reputation around here if anyone needs plastics and fabrication done. I'll be going with G10 for most of my backing plates except for a couple of stainless steel plates.

 

[markvone]

Norva Plastics +1

Norva Plastics is also the source of most of my G10 on Ebay. They probably sell small pieces and scraps on Ebay. I also get King Starboard and plexiglass on Ebay from Norva.

I would contact them directly for larger projects.

www.norvaplastics.com
(757)622-9281

Mark

 

[garryh]

I think feathering the edges and radiusing the corners is quite important in order to not create hard spots which will damage under constant flexing.
Question... G10 is extremely expensive stuff but sometimes necessary. For backing plates I am planning on using frp chunks from the hulls of a couple of derelict boats in the yard, will clean them up and epoxy in place, laminate to whatever thickness but likely already 1/4" anyway, fender washers under all nuts. Any problems you can see with this? tks

 

[Loren Beach]

I think feathering the edges and radiusing the corners is quite important in order to not create hard spots which will damage under constant flexing.
Question... G10 is extremely expensive stuff but sometimes necessary. For backing plates I am planning on using frp chunks from the hulls of a couple of derelict boats in the yard, will clean them up and epoxy in place, laminate to whatever thickness but likely already 1/4" anyway, fender washers under all nuts. Any problems you can see with this? tks

Recycling old laminate cutouts is a great idea. I have done that with old "circles" for the instruments heads from our prior boat.

If you have any hesitation about the inherent strength required, you can always use a piece of G10, but most of the places we have put in backing plates, like thru hulls and stanchion bases could use recycled hull pieces.
Whatever you choose, just clean and scuff it up with some 60 or 80 grit, and it will bond solidly with thickened epoxy.

Loren

 

[garryh]

thanks Loren. The other thing one would need to do would be to use a wax remover to get rid of all traces of mould wax or other applied waxes before bonding.