marine craft has a crushable frontal impact protection structure , comprising transverse bulkhead protecting passenger area ; longitudinal crushable tubes ; and transverse member . webs strengthen tubes , which may be made of extruded , heat treated aluminum ; stainless steel ; or plastic . tubes are splayed to improve protection against angled impacts . the forward ends of tubes are tapered to initiate deformation . tubes may be hexagonal , round , or oval in cross - section . longitudinal bulkheads , and a transverse bulkhead may be used in place of tubes . longitudinal corrugated sheets may be mounted transversely . the bow area may be filled with deformable cellular foam to act as a buoyancy aid . side and rear impact protection is also provided .