As most sailboat decks are cored with balsa or some other material any area which is load bearing, or where items such as chain-plates pass through the deck, should have the core removed and the void filled with epoxy or similar. Whitby Boat Works seem to have done the job right . This is a photo of the area where the mizzen chain-plates passed through the deck. Absolutely no water in the core, because there is no core.
The bulkhead which the chain-plate was bolted to did not fare as well. Two chain-plates were secured between a grp panel and the plywood bulkhead of the heads. The plywood suffered considerable water damage where the bolts went through. As I will not be using this area as to support chain plates git-rot or similar will solve the problem. Anyone who is replacing the chain-plates on a Whitby should pay a little attention to this bulkhead.