" With the beam above the deck, the hole in the leeward wall takes all the loads, but the outboard end sits on the bridgedeck and needs to be tied down to the side of the hull. This is the primary load and it is better if it is taken by the hull rather than the lashing. "
I was under the impression when watching the picture at 1:26 on the sol making video that the underside of the seat was also walled off on the outboard side with the cockpit entrance panel. As this panel would be bound to the inner side of the hull there is no need for a lashing as a hole can be made in that panel in much the same fashion as the one in the hull for the beam below deck.
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