Researchers in Korea have developed a new path-following technique for autonomous ships (writes Nick Flaherty).

An essential function of maritime autonomous surface ships (MASS) is the ability to follow a pre-determined path at sea, considering factors such as obstacles, water depth and ship manoeuvrability. Any deviation poses the risk of contact, collision or grounding.

Current methods for assessing the path-following performance of autonomous ships rely on simplified mathematical ship models. Unfortunately, these models cannot capture the complicated interactions between the hull, propeller, rudder and external loads of ships, leading to inaccurate estimates.

The researchers at the Korea Maritime & Ocean University used a free-running computational fluid dynamics (CFD) model combined with the line-of-sight (LoS) guidance system at low speeds under adverse weather conditions.

A CFD-based analysis of the popular KRISO container ship model, equipped with the autonomous LoS guidance system, modelled adverse weather as disturbances from the bow, beam and quartering sea waves. These three cases were studied at three different speeds to identify the effect of forward speeds on path-following performance.

Simulations showed the ship deviated from its course in all three cases. In the case of the bow and beam waves, these deviations decreased with an increase in propulsion power.

Interestingly, in the case of quartering waves, propulsion power had a negligible effect on deviation. Additionally, the heave-and-pitch responses of the ship were heavily influenced by the direction of the incident waves.

In all three cases, the roll amplitudes were consistently below 1.5o, but the team could not ascertain the effectiveness of increasing speed to improve path-following performance.

Instead, the study showed that increasing propulsive power reduces deviations from the predetermined route when the ship encounters bow and beam waves. This research contributes to improving guidelines for minimum ship powering for autonomous navigation systems when operating in poor weather conditions.