marine craft has a crushable frontal impact protection structure , comprising transverse bulkhead protecting passenger area ; longitudinal crushable tubes ; and transverse member . webs and strengthen tubes , which may be made of extruded , heat treated aluminum ; stainless steel ; or plastic . tubes in figs . 5 to 7 are splayed , to improve protection against angled impacts c . the forward ends of tubes are tapered , to initiate deformation . tubes may be hexagonal , round , or oval in cross - section . fig . 8 shows longitudinal bulkheads , and transverse bulkhead in place of tubes . fig . 9 shows longitudinal corrugated sheets ; these may be mounted transversely . fig . 10 shows how area filled with deformable cellular foam , to act as a buoyancy aid if hull is breached . side and roar impact protection is also disclosed .