Damage stability requirements 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, but amendments in the existing regulatory framework will be needed. 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 index gives a requirement for the allowed probability of sinking when a ship is damaged due to collision. 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. 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. Consequently, a lower subdivision index might be accepted for unmanned autonomous ships. In this article, the damage stability-related level of risk of a manned ship will be derived by means of a risk analysis. Thereafter, the subdivision index for unmanned ships, which ensures an equivalent safety level to similar manned ships, is established for three individual ships. The assessment shows that a reduction in the subdivision index is allowed for unmanned ships and that the reduction will be largest for smaller ships.