Backing Plates

[JohnnyC]

Its time to replace some deck hardware and I am looking for advice.

Will aluminum make good backing plates or would stainless be a better choice?? Which alloys?

I suspect the aluminum would be easier to work, but don't know if it will be as durable or as strong. Don't have any real experience working with metal.

Thanks for any advice you can offer.

John

[FrankZ]

I had to redo some backing plates that had been done in plywood. I opted for 16 gauge stainless (304). One was an odd shape and Metal Express cut it out to match the template I made, though had I gone thicker they said I would have to cut the shape myself as the machine they could do the shape could only handle up to 16 gauge.

Metal Express - Home

They don't do fabrication or drilling and I had to buy a rectangular piece big enough for both plates, but pricewise it was fairly cheap (about $35 and I have the scrap bits which are big enough to use in other spots). They do have shops all over and a web order system.

[JohnnyC]

Thanks FrankZ

I checked the metal express website and it looks like they have whatever I need.

Are you happy with the 16 gauge or would you like to have been able to go thicker??

John

[GordMay]

16 Gauge is pretty light stuff (< 1/16" thick) for a backing plate. I wouldn’t use anything lighter than #12 Ga. (or 1/8" plate), or thicker for structural backers.

[Pblais]

Aluminum addds an extra problem since you'll be using Stainless Steel bolts for most deck mounted items. The dissimalar metals issue just makes it more complicated. 304 Stainless would be a decent choice since you really don't need 316 SS for a backing plate application. You do need to seal the holes and bed all the items in addition to using a backing plate. It's all these things you never see that really matter most.

[GordMay]

I’ve never had a problem with galling on Aluminum Backing Plates, fastened /w Stainless Bolts & Nuts.
I oversize the holes in the backers slightly, and seal & isolate /w sealant.
Nothing wrong /w Stainless, if you can afford the slight weight penalty, and can work it (drill & cut).

[FrankZ]

Originally Posted by GordMay

16 Gauge is pretty light stuff (< 1/16" thick) for a backing plate. I wouldn’t use anything lighter than #12 Ga. (or 1/8" plate), or thicker for structural backers.

When speaking with the fellow that cut it he suggested that this should be fine based on the type of load it would take to bend it. He suggested it would take at least 5000 pounds on a bending machine.

I have a 25 boat. From the chart someone posted (could have been you) about breaking size of wire rope the plate should be stronger than the headstay, and it is fairly big (little over 1 sq foot) in the bow.

Dealing with a bigger boat I would be more apt to look into something thicker. However, I was on a Columbia 45 that appeared to use the same thickness for winch (job) backing plates with less square footage involved.

I have been keeping tabs on it during and after sails and so far it looks like it is maintaining shape.

[SkiprJohn]

Captain Kirk gave us an idea about using the thick plastic cutting board material that you find in WalMart as backing material. I'm going to do it. It certainly would not corrode and it would not rot or delaminate. All features I like but then again would it be strong enough. I think it would.
Kind Regards,
JohnL

[windborn]

G10 / FR4, a very stable industrial laminate with very high mechanical strength, works pretty well for backing plates. It is easy to work with, uneffected by moisture or temperature, and can never corrode. You can buy sheets of various sizes from McMaster Carr.

[delmarrey]

I use SS myself. There use to be alum. but you should have seen the alum. oxide that came out from under them. It swelled up so bad it left dimples on the underside of the deck. And where the alum. track use to be it left dimples on the top side of the deck.

USE SS the only way to go.

But what ever you use, here's a simple test. Put a tapered punch in the hole and hit it with a 5# hammer. That'll be about the same effect that a bolt pulling on the thing will have over time.

[JohnnyC]

Thank you to all who shared their knowledge.

This is a great place to learn.

Looks like the most trouble free, time proven solution is stainless steel at .125 inches or greater thickness. 316 grade not required for interior use.

Now its time to learn simple metal working.

Good thing working on the boat is nearly as much fun as sailing her.

John

[Pblais]

The ability to use other than 316 SS is related to how well a job you do on the bedding and sealing part of the job. There is no question that aluminum can do the job structurally but if the bolts leak you have a problem in any event. Backing plate failure isn't the only issue. 304 SS is not a bad choice but if it leaks you'll have other troubles waiting for you. With a cored deck the other troubles could be worse.

[delmarrey]

Cored decks are not much trouble if one preps them first with epoxy filler.

The trick about drilling stainless is go SLOW and use a lubricate. Colbalt drills are preferable. Cutting the plate is a problem at home. It's better to have it sheared to size. Sawing requires slow speeds and coolant. Machining on a lathe is no problem. Milling requires a coolant.

304 works up on deck OK if it's highly polished................................._/)

[FrankZ]

Originally Posted by delmarrey

Cored decks are not much trouble if one preps them first with epoxy filler.

The trick about drilling stainless is go SLOW and use a lubricate. Colbalt drills are preferable. Cutting the plate is a problem at home. It's better to have it sheared to size. Sawing requires slow speeds and coolant. Machining on a lathe is no problem. Milling requires a coolant.

304 works up on deck OK if it's highly polished................................._/)

I bought a table top drill press and used the recomendations for speed in the manual with tianium bits. Kept a bit of oil on the spot and it took less than a minute per hole (close to a minute for the 5/16th holes). I am quite thrilled I didn't have to cut it myself.

[CSY Man]

My boat came from the factory with 316 SS chainplates and Alu backing plates.
After 24 years I replaced the lot.
The backing plates were in fairly bad shape, but not completely gone.
Replaced 'em with 316. SS

That being said, I used alu backing plates for my SS cleats with SS bolts.
6 years ago and I see no problems. (Backing plates in the V-berth ceiling, I look at them every time I go to bed...err, bunk..Gave 'em plenty of caulk and paint however..Get the occasional salt water in and around the backing plates and they may go for a shorter lifespan. )