On the Seakeeping Operability of Naval Ships

The operability of a vessel in the sea environment, i.e. the capability to accomplish its mission is a major performance indicator of the vessel. It is well known that adverse sea conditions induce significant dynamic motions, velocities, accelerations and loads, which deteriorate the performance of both the crew and the various subsystems onboard, including the hull form itself. For example, the operation of medium and large naval ships e.g. destroyers, frigates and corvettes depends highly on the capability of the helicopters onboard to take-off and, more important to land. Otherwise, they are vulnerable to the attack of submarines. In severe wind and sea conditions and in order to ensure a convenient air wake field operation of helicopters, the captains use to manoeuvre their vessel so that they sail in quartering to following sea conditions. Furthermore, the specifications of the helicopters operating on board ships provide maximum acceptable values (criteria) which should not be violated in order the take-off and landing procedures are safe. Thus, the operation of the aircraft and especially the helicopters depends on the motions of the vessels in a seaway. In this paper, the current practice in the design and operation of naval ships to ensure its operational availability in specified sea conditions will be analyzed and the pertinent existing criteria will be reviewed. Additional information contained in NATO STANAG 4154 will be discussed and a framework of procedures to satisfy all involved subsystems will be proposed. Available methods to improve the performance of existing vessels or new designs will be presented and discussed.