Kurt,
the end result of your mast beam project will be zero flex of any sort.
As to the deck flexing, I believe it has to be rotton core. Right? Like 338 you may have a composit whose inner layer is damn thin. In the past I questioned whether a recore could be done from the top because the inside had little or no integrity. I found a single layer each (on the inside of the composite) of cloth and mat under the mast. Easily moved with the fingers. I've just assumed that later number boats were skimped on, but it may be individual ones.
I believe now when doing a radical coresectomy that the foredeck area should be carefully supported from inside with boards and battens or even an inflated bag or two. Cutting the deck out in small sections at a time so as not to loose the camber of the deck.
No bulkhead or knee was built-in to the underside of the deck/cabin roof in 338. Seems to be the way it was done back then. I would make sure they are well tabbed in this time so that the deck becomes part of the system, not a symptom of something wrong. How this can best be done is obviously open for discussion. The forward knees for the lowers ought to be able to support the deck. Wide tabbing and healthy core would take care of any flex in this area. No?
{The widest part of the foredeck and the rounded nose of the cabin is unsupported from inside - except by its monocque shape and the sides of the hull. Flex in this area would be strange - unless it was contributed by weakened deck.
The mast is supported by the whole top of the cabin and indeed by the whole top of the molded deck. Imco it's possible that some of the downward force of the mast could be translated into that cabin-nose/wide foredeck area. Loss of camber would be an indicator. Long straight-edge would show it.}
I managed to get glue under the liner port and starboard sides and carjack the sags and openings 338 had there up flat to the roof - I felt very uncomfortable messing with the liner so I opted for monolithic knees off the hull. I may go back and tab them in to the top. (But I might also remove them because my chainplates are going on the hull.) The liner as you know does not extend all the way out to the hull under the side decks so there is actually some prime attachment for part of the top of the aft knees (aft lowers) and the main bulkhead (or what remains of it under the decks.) Would not tab onto the liner. The knees tabbed in solid must contribute a good deal of stiff to the hull and deck in way of the shrouds what ever method of chainplate attachment.
IMHO, NOTHING should be able to move in the shroud/mast/deck/cabin/beam area. That is, nothing of the boat itself (the plastic) should move at all. The rig depends on it. The shrouds in big water can't suddenly get loose because of 'oilcanning' of hull or deck and not support the mast, both sides. Sudden loose shrouds could be a cause of the mast breaking in a knock down, doncherthink?
It does seem far fetched: but if the weight of the boat is supported by the mast (ala Sponberg) then two tons of concentrated force could do some strange distorting of plastic laminate! Would have to see it to believe it - like in frame by frame time lapse. Monocque structures can be crushed, I'd think they can be twisted on an axis, and relative flat thin planes can be oil-canned. Generally '60s plastic lams were substantial and made from excellent ingredients. That's what we gather, anyway. But composits with cores must have been fairly new and simple back then - now we know that the opposing skins must be equal in strength/thickness. David Pascoe, our favorite online marine surveyor talks about this on
http://www.yachtsurvey.com/HiTech.htm
I feel that the mast bulkhead along the hull from the deck down to the keel has to be very strong WITH WIDE TABBING. - and ideally the bulkhead should be connected across the keel, so that mast forces are shared on both sides of the boat. As above, so below. The circle must remain unbroken...in the bote, load, in the bote....
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