Backing Plate Recommendations

[coopec43]

[QUOTE=Bowdrie;3915956]OP, it's plain to see from the pic that the preponderance of water coming in is thru the fastener holes.
Look at the fastener holes in the stanchion bases, you'll see that the holes are at most ~3/8ths" from the edge. The flexing of the bases, (huge amounts of leverage are exerted against the bases,) leads to the water migrating from the edge of the bases to the bolt holes.
No matter what you use for an internal backing, unless you stop the water on the outside from getting to the bolts there will be leaks.
Answer: take some 3/8ths G10 and make external pads for the bases to sit on, make those pads at least 3/4" bigger all the way around than the bases.
Now with good caulk/sealant the bases will not be subject to standing water and you have a much longer pathway at deck level, (more sealant,) to resist water.
Use large washers under the bolt heads on the outside also.
It helps to have small countersinks in the deck to hold an "O-ring" of sealant.

QUOTE]


I did something very similar. I made up a sheet of f/g about 10mm thick and used it to make pads which I epoxied to the deck under each stanchion base.

No more leaks!

[Iron E]

IMO, the backing plate materials you list are fine... as is G10
If you do use aluminum with SS hardware, use Lanocote or some form of corrosion barrier.

You may have water intrusion (from your picture). I use Bed It Butyl for mounting deck hardware.
If water has made it into your core, you have another issue to address.

Of course, follow proper Potting techniques when rebedding your stanchions.

[OS2Dude]

When I backed my cleats, I also cored the holes in the deck. (Drill oversized to inner lining, fill with thickened epoxy, redrill correct size hole.) I also tapped the epoxy and the backing plate (Held in place with smaller bolts to start.) If the underside is rough glass, you will need to use something like a Dremel tool to smooth it out so the backing has a good contact.

[Cheechako]

Originally Posted by djousset

Thank you for the responses, good info.
I am not overly worried about costs, I have family that can provide/manufacture both stainless and aluminum, and I have a good source for G10. Apples to apples, what is the hierarchy of these three materials on the combo of strength and durability? One stanchion in particular at the starboard side gate gets a lot of activity.

Aluminum is far more flexible than SS. It's Modulus of Elasticity is roughly 1/3 of SS. A backing plate tries to spread the load over a wider area, thus avoiding point loading. The more it flexes the less well it would do that. So stiffness is probably more important than strength, especially if it's over an cored area.

I dont know the modulus for G10 though.

All this is probably overkill for a stancion with 4 bolts. I'd probably go with 1/4" Aluminum for ease of fabrication and call it a day. Thicker the better if there's room to avoid flexing the deck. Or G10 if it has good Modulus numbers.

[torrmundi]

Originally Posted by Cheechako

Aluminum is far more flexible than SS. It's Modulus of Elasticity is roughly 1/3 of SS. A backing plate tries to spread the load over a wider area, thus avoiding point loading. The more it flexes the less well it would do that. So stiffness is probably more important than strength, especially if it's over an cored area.

I dont know the modulus for G10 though.

All this is probably overkill for a stancion with 4 bolts. I'd probably go with 1/4" Aluminum for ease of fabrication and call it a day. Thicker the better if there's room to avoid flexing the deck. Or G10 if it has good Modulus numbers.

I found online references of about 28Mpsi for 316 Stainless and 2.2-2.7Mpsi for G10, depending upon the direction of strain.