I'll be making some stanchion base backing plates for my boat sometime soon,
and was wondering what size/thickness they should be. The boat is 18', GRP,
and there are no backing plates at present (3 stanchions each side). The
bolts come through into the cabin and the plates would bear against the GRP
cabin ceiling.

The plan is to use stainless steel plate, partly for corrosion resistance,
and partly because of the way the stanchion bases were aligned when they
were originally fitted - they aren't all set out such that all through-bolts
are clear of the internal cabin wall (ie, some of the nuts are very close,
such that some plates would have a slot in the outer edge, rather than three
clear holes). I feel that a softer material, such as wood or brass, might
give at the edge and not do the intended job.

What thickness of stainless should I use? 3-4mm sounds good from a
fabrication point of view, but would it be adequate?

The bases are 62mm in diameter (about 2.4") - how wide should the plates be?
I was thinking of a rectangular shape with the long side running fore/aft.
Maybe 3" wide and 6" long.

Given that the cabin ceiling isn't perfectly flat, how should I attain a
good contact over the area of the plates? Would a layer of thin (1-2mm)
rubber help? Or should any packing be solid?

What about rotating those bases that are poorly aligned, so that all three
holes are clear of the inside wall, filling the old holes and drilling new
ones?

Any other ways to approach this? Comments invited.


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.