Another metalurgy question...

[merttan]

Hi everyone,
I'm going to add stanchion base support plates below deck. What do you use for support plates? I thought of wood plates but why add another another rotting material in cabin?
What are your advises?
The boat has washers as stanchion supports now and stanchions move when I push them hard enough...

[T34C]

Wood is only a "rotting material" in the cabin if it gets wet. If done well there shouldn't be any water intrusion that would create the problem.

[DrB]

I know that there are some instances where wood is used as a backing plate material, but for stanchion backplates, stick with stainless or aluminum.

Wood will swell and contract overtime. You want something that is dimensionally stable for your backing plates and also hard to really be able to tighten down on the bolts without creating indentations in the wood from the washers.

DrB

[hellosailor]

I might go with Delrin (aka UHDPE, etc.) plates, which are easy to cut and drill, and then use stainless barrel washers and nuts to secure the bolts and spread the load into the plastic. The plastic will conform somewhat to the underside of the deck, but if that's not a smooth and level surface, some epoxy putty or bedding compound might be in order as well. And a thin solid neoprene gasket under the stanchion base on deck itself, since there will always be some motion there and the gasket will help prevent both leaking and cracking when that happens.

[DrB]

And a thin solid neoprene gasket under the stanchion base on deck itself, since there will always be some motion there and the gasket will help prevent both leaking and cracking when that happens.

If it were me, I would not do this. A neoprene gasket only under the stanchion base is not any type of bond that will hold water out. It's a temporary seal at best, and not a good one for a dynamic environment. There was a thread on this a few days ago.

I would use a good bedding compound on the underside of the stanchion base

DrB

[cardiacpaul]

you could alays use these...

Catalina Direct: Stanchion Backing Plate for Trapezoidal Base ?90->

[KODAD]

Would 'starboard' be a better alternative to wood?

[Rockter]

Aluminium is very much easier to work. It is soft, can be drilled readily, and can be filed easily.
Stainless, though pretty, is hard and difficult to work.

[KeelHaulin]

I vote for aluminum also; plastics can crack and if the backing plate lets go the stanchion would be break free. The best material is probably aluminum although it will get some galvanic corrosion if water leaks. It will be sooner that you re-bed the stancions than a 1/8 piece of aluminum sheet will fail due to corrosion though.

[hellosailor]

DrB, the best advice I've probably ever seen is to use bedding compound, as you suggest, but to also use o-rings in order to ensure it cures to a certain thickness--and then go back a second time to torque it down. That's a lot of work, compared to just using neoprene gaskets. After all, even engine cylinder walls are held with gaskets, the trick is the proper installation of them.

KH-
Plastic isn't all the same stuff you know. Delrin and UHDPE can be extremely strong in compression. Perhaps more so than the decking they are bolted to. They've been used for mast steps eithout any problem, and very little else on a boat gets that much squeeze on it.