It would be good if a naval architect/engineer responded to this chain. I would assume when a boat is designed, the NA and engineer design the vessel for the proper strength required for the size, displacement and performance. This would also be in relation to material being used. I would also assume regardless of the material used, the ultimate strength would be the same as that is what is required by the engineering, design and code requirements. For example, the same boat built in steel would have a 1/4" thick hull plating, or 3/8" aluminum plating or 3/4" fiberglass laminate. I do not think a vessel is deigned to be weaker than the same boat in a different material. Ultimately the vessel has to meet the engineering requirements for that code requirement, regardless of material. The materials might have advantages/disadvantages over each other, but the engineering tries to remove that in order to meet the same result in strength. I work for a company that does our own fabrication using ferrous and non ferrous materials. When we use aluminum, it is often thicker than if using steel as we need to match the strength of steel. This can be done if we go thicker. The problem with aluminum is stress over time and not being as compliant as steel (breaking instead of bending). I would assume fiberglass laminate could be made to have strength and ability to absorb a certain amount of energy before cracking. A materials expert in boat construction would be able to shed more light on this topic. This comes up quite a bit and it I have yet to see an engineer chime in.