Mast Base

[lw395]

The deck seems solid under the mast base... no obvious signs of rot and the stainless bolts were untarnished and dry. However , as in image below, the deck is depressed about 4-5mm in the centre.

So, plan currently is not to cut the deck open....

This said, still need to figure out how best to sit a flat plate on the curved deck, due to the compression.

The timber plate was also tapered, 28mm fwd and 10mm. Assume to level the plate.

I'd drill some holes in that and see what's inside.
Maybe fill it with resin.
Mask around it, pile on some glass and resin, file flat.

 

[LittleSister]

I've seen more than one boat where the real problem is at the bottom of the post.

Yes, it's not uncommon. Some marques are particularly vulnerable because of the design (e.g. steel bracket under the post disintegrating through rust), I've also read of mysterious subsidence in seemingly solid built-up GRP.

 

[Rappey]

This will probably sound a little crazy but car body filler could be used to build up a level plinth.
I was astounded to discover that under a large heafty mast.. Seems it is very crush proof !
The concave curve of your deck under the mast says to me the substrate (probably ply) is soft and will crush when a mast is loaded on it, but when walking it will feel fine.
Put a new T bar mast base on and it will get bent again if the deck and whatever is in it gets crushed.
As a quick but not so great fix, bore lots of holes under the mast base (not penetrating the interior) and epoxy fill. Your mast will then sit on epoxy piling.. lol