Sorry wasn't very clear. The shape of a well-designed boat gives it a lot of strength (double-curvature). Early attempts to produce GRP versions of boats designed to be build in plywood were very unsuccessful as the flat areas were weak and had to be built much too heavily to (try) to make them strong enough until reinforcing with suitable materials was introducted. High-performance boats plane which needs relatively flat aft sections so the use of reinforcing (foam sandwich construction) was essential.
White decks are not popular because of the glare but white hulls are - they are easy to see when they are inverted. But dark decks are not popular either - a pale grey works well for preventing glare.
High-performance boats have massive rigging tensions and some are built round a metal monocoque frame that takes those tensions. In dinghies the frame can be seen - International 14s are a good example.
High-performance boats are cossetted. Dinghies are kept off the water and under covers except for the few hours a week they are sailed. Serious keel-racers take the boat off the water and cover it between races for a variety of reasons. Boats used by sailing schools (especially marine-based ones) look pretty tired pretty quickly.
So yes, the composite part of the structure does matter but it's by no means the only part of the story, and the forces involved are certainly not the number of Gs that quite a few gliders are designed to withstand -
Also, the consequences for most sailing types of a structural failure are nothing like a serious as those for aviators. Obviously in ocean racing it can be, though there have been some amazing rescues (Tony Bullimore for example). The element that fails most often is the rigging, not the hull.
I'm not sure how the stresses of sailing compare to flying. A common training glider will take between +6.5 and -4 g, and I doubt anything sailing ever experiences those extremes. However a prolonged upwind leg, or a planing downwind one will involve plenty of slamming if the seastate is rough and the wind is brisk. (though the bows are inherently very strong because of their shape)