I am amazed at some of the misconceptions being put forward here... There's nothing wrong with a cored hull, even below the water line, and in fact a properly done cored hull will have more strength and far better proprties in terms of strength, and damage tolerance than an equivalent weight solid hull. Remember that in any surface that is stressed in bending, the high stress is only in the outer fibers, the middle of the surface (or beam) is only stressed in shear. So long as the core is sufficiently strong in shear and the outer skin is strong enough to withstand local impacts a cored hull is far superior than a solid gfrp hull. Problems come in when the outer skin is not thick enough to prevent the core from being damaged by deflections of the outer skin. Look at an old surfboard and see the delaminatons from getting beat around and you will see what happens to a brittle core with a thin skin. Some builders are saving a lot by thinning out the skins, and such a hull will be stiff, but won't have the damage tolerance of a hull done right. The core material makes a huge difference too, with PVC materials like Airex being much stronger and more damage resistant than some of the cheaper materials. Bottom line is know your builder and if he uses a cored design, find out how thick the skins are and what the core material is and you will be fine.