Making your own backing plates?

Brian S · Mar 3, 2014

Check out Cap'n Pauley's article on backing plates in the current issue of Good Old Boat magazine.

I wonder if it's cost effective to make your own plates, or to just buy some G10?

Also, a glass fiber matrix does not gain strength from the resin. That's why we now vacuum bag laminates for maximum strength, rather than hand layup. For this reason, I would be more inclined to do my own woven roving layup with epoxy on heavy polyethylene sheet (for ease of removal.)

Keep in mind that chopped strand mat has polystyrene binding agents intended to dissolve when used with polyester resins. Although West Systems says you can still use it with epoxy, it won't wet out quite as nice as woven fabric.

Just my $0.02....

Maine Sail · Mar 3, 2014

Not how I would do it as it is very resin rich and resin has little strength. Perhaps the easiest method is to simply use G-10 or GPO-3 pre-made fiberglass sheet.

Short of that wax a piece of glass, lay down some mat, roving, cloth etc. and build up the layers.. I can make a piece about 1/2" thick in 2X2, 3X3 etc. in about 15 minutes once you get everything ready..

This is what some of my home made sheet looks like...

FastOlson · Mar 3, 2014

Backing Plate thoughts

I have molded out some small parts with cloth and epoxy resin. Not having vacuum bagging means at hand I just put some plastic sheeting on top, some 1" foam, a board and about 30# (or more...) of weight. Seems to squish out the excess resin fine.

I found out years ago that for small jobs it was cheaper to just buy some G10/FR4 pre-made material, especially for stuff like flat backing plates.

For a project needing a right angle part, I bought the pre-made material from McMaster Carr. Nice guys to deal with and the price was right.
If I buy locally I even have a plastics supplier that will cut to my specs with their diamond-blade saw for no extra cost.

As Maine pointed out, there's no strength at all in casting something with resin with a bit of fiber thrown in.

Just my .02.

Loren

Bill Roosa · Mar 3, 2014

is there something wrong with a piece of wood?
A good 3/4" piece of oak is what I use. home depot has them in stock and they are pretty easy to shape.
It does not hold the boat together and just needs to be able to take somebody standing on the thru hull and not break.

FastOlson · Mar 3, 2014

Bill Roosa said:
is there something wrong with a piece of wood?
A good 3/4" piece of oak is what I use. home depot has them in stock and they are pretty easy to shape.
It does not hold the boat together and just needs to be able to take somebody standing on the thru hull and not break.

Wrong? No... but what with the chance of some outside water someday seeping in around the thruhull or some inside water (condensation, or whatever) slowly getting into the wood, it'll rot someday. Nice to do it the best way in the first place, IMHO.

Loren

shemandr · Mar 3, 2014

I'm going to install a swim ladder on my runabout this spring. I weigh 250 lbs and all of that will pull on the ladder mountings. Any suggestions for backing plates? Oh since the bolts will have to be as low as possible on the transom to get two steps underwater, the backing plate will have little meat to the waterline side.

gettinthere · Mar 3, 2014

I take the piece of wood one step further. I soak it with penetrating epoxy, sealing out that moisture.

25yearslater · Mar 3, 2014

Mainesail has the same method I used to plug all the holes YOT accumulated over the years, Jonny. I used biaxials and epoxy for everything and am happy to report that everything is performing without problems. You may recall I was plugging above and below the waterline and incorporated a few nifty rabbets to seat everything. My mainsheet chainplate has a 3/16ths biaxial backing plate just for good measure and no cracks or otherwise.

thinwater · Mar 3, 2014

What Mainesail said. There are many variations, all of them cheaper, faster, better looking, and stronger.

The only exception, for me, would be an area so curved I could not bed the FRP plate. In that case I simply hand lay some glass on the inside, perhaps including some prelaminated FRP as well. I've done this for bobstays.

Bill Roosa · Mar 3, 2014

Olson
Ok wood rots, Care to comment about wooden boats and their rot problems?
I mean seriously Olson. What kind of moron do you take me for? Of course you are going to water proof the wood.

Maine Sail · Mar 3, 2014

Bill Roosa said:
Olson
Ok wood rots, Care to comment about wooden boats and their rot problems?
I mean seriously Olson.

Come to Maine and visit any of our wood boat shops and you will see they make a mint keeping these boats afloat. Six and seven figure rebuilds due to rot are not uncommon at all..

Bill Roosa said:
Of course you are going to water proof the wood.

Just too bad the vast majority of boat builders never did that.. One of the biggest reasons I replace or re-install seacocks is not corrosion or wear but rotted wood backing plates...

BTW this is a $200K+ boat and the photo is recent... Think this customer got their 200K+ worth...? Bare Home Depot grade ply...??

wufibugs · Mar 3, 2014

What about using starboard for this application? Or is the problem that unless you use the special cement, you can't get the stuff to stick to anything?

Maine Sail · Mar 3, 2014

wufibugs said:
What about using starboard for this application? Or is the problem that unless you use the special cement, you can't get the stuff to stick to anything?

Problem #1 very little strength, flexes easily.

Problem #2 nothing likes to stick to it.

Sprega · Mar 3, 2014

A well designed, well built, well maintained wooden boat will have very little problem with rot.

Brian S · Mar 3, 2014

So sorry, JonnyQuest, that article on backing plates was in the March/April (current) issue of Small Craft Advisor, not Good Old Boat. I get my 2 primary sailing mags confused from time to time

Oh, and the article was about proper backing for deck fittings, not through-hulls. Sorry about that. Capt'n Pauley's main point was to taper the edges of the backing plate. He says Starboard cold flows under pressure. Maine says nothing sticks to it, which pretty much confirms for me that it is just a high modulus or ultra-high modulus polyethylene product.

Ralph Johnstone · Mar 3, 2014

Maybe .........................

Maine Sail said:
BTW this is a $200K+ boat and the photo is recent... Think this customer got their 200K+ worth...? Bare Home Depot grade ply...??

.......................... if he was willing to spend $200,000.25, he might have received some decent pipe dope on the theads of the various pipe fittings. They're all leaking due to cheap brittle pipe dope.

If you suffer from obsessive compulsive disorder (OCD) as I do, you'll use 3-4 wraps of teflon tape followed by wiping the surface of the tape with Permatex #2 sealant on below waterline threaded pipe fittings.

Maine Sail · Mar 4, 2014

Sprega said:
A well designed, well built, well maintained wooden boat will have very little problem with rot.

By well built and designed and maintained does a Concordia count?

Other than some rotted frames and back bone this boat had been exceptionally well maintained by even the most critical wood boat standards..

This repair exceeded the cost of this boat when she was new, by a long shot.. Course if you can afford to own a Concordia...... A repair like this is probably like you or I buying a can of varnish..

Making your own backing plates?

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