Table 2.

Details of the physical defence subsystem of the SRMS.

Composition	A collection of hardware-based risk mitigation instruments, signs and facilities.
objective	From the perspective of physical risk mitigation, giving full play to the passive resistance of objects, reducing, delaying and avoiding possible risks, and then improving the effectiveness of water traffic risk mitigation.
function	Based on the characteristics of a physical object, playing the role of barrier, identification, and damage resistance of physical prevention.
characteristic	Advantage: good damage resistance (compared to humans), high permanence (24 h on duty), excellent economy (compared with personal injury), strong replaceability (replaceable after damage), strong objectivity (fixed attributes).
	Disadvantage: poor autonomy (no self-awareness), poor flexibility (almost no interaction), poor lifting performance (cured performance).