Assessment of the Required Subdivision Index for autonomous ships based on equivalent safety

In recent years, a significant amount of research has been conducted on autonomous ships. Since it is assumed that these ships will sail with a significantly reduced crew or even without people on board, the design of the ship needs reconsideration. The absence of people on board and the associated safety measures could result in a more efficient design. However, to achieve the required design freedom, the existing regulatory framework will have to be amended. In this article, we will focus on potential changes in the Convention for Safety Of Life At Sea (SOLAS) and in particular on the Required Subdivision Index. The evaluation is performed by using the principle of equivalent safety, which will ensure that unmanned ships will be at least as safe as manned ships. The index gives a requirement for the allowed probability of sinking when a ship is damaged due to collision or contact. The safety level is related to the safety of ship, cargo, environment and crew. If the crew is no longer present, the consequences of an incident will be less severe, since the probability of casualties is no longer present. If the principle of equivalent safety is applied, a lower subdivision index can be accepted for unmanned autonomous vessels. In this article, the level of risk that a manned ship is subjected to will be derived by means of a risk analysis. In this risk analysis all logical consequences of a collision will be taken into account, covering both the probability of losing the entire ship and the consequences of the cases where the ship will not sink. Thereafter, the Required Subdivision Index for unmanned ships, which ensures an equivalent safety level to an equivalent manned ship, is established. The sensitivity of the result to changes in the data is discussed as well.