The research effort on autonomous ships has increased over the last years. The realisation of these ships will have as a consequence that the crew can be reduced significantly or even be removed entirely, resulting in unmanned ships. Although there is a strong belief that unmanned ships would lead to more economic efficiency, only limited research has been performed in order to demonstrate what the overall effect of the change to unmanned shipping would have on transport costs. Nonetheless, more reductions in cost or improvement of transport performance for unmanned ships would make them more attractive and economically viable.
The design of a ship is subjected to regulations and requirements that limit the design freedom, but it increases safety. Removing the crew from the ship reduces the risk of shipping, under the assumption that the probability that an incident occurs does not change, since the lives of the crew are no longer at risk. If the risk is lower, the requirements to the design of unmanned ships might become less strict, while maintaining equivalent safety. In this way more design freedom can be realised for unmanned ships, as well as more economic efficiency.
Within this report the required subdivision index will be evaluated, for it is expected that reducing this requirement can create more design freedom. Therefore, this research will focus on what reduction in the requirement concerning damage stability for unmanned ships can be allowed, if they are subjected to an equivalent level of risk as manned ships of the same size and type.

It has been found that the required subdivision index can be lowered for unmanned ships, based on equivalent safety. The contribution of the risk of losing lives to the overall level of risk is larger for smaller ships. This is reasonable, since for larger ships, the size of the crew increases with a lower rate compared to the amount of cargo, installed power or capital costs. Therefore, the allowable reduction in the required subdivision index is largest for smaller ships.
However, the size of the reduction depends strongly on missing accident statistics concerning the loss of life. The missing data results in the following uncertainties, for which further research is recommended.
Firstly, for different ship types differences in the accident statistics are present. There are significantly less fatalities related to bulk carriers and container ships compared to general cargo ships. It is expected that these differences are related to the individual ship size and crew size, for which both the correlation with the probability of losing life is unknown.
Secondly, there is a discrepancy between the theoretical probability of survival of a ship, namely the attained subdivision index, and the probability of survival that the accident data suggests. The attained subdivision index suggests that at least 30% of all accidents should lead to a total ship loss. The accident data reveals that for general cargo ships around 10% leads to a total ship loss.