Research on the Improvement of Safety Navigation Based on the Shipmaster's Control of Ship Navigational Parameters When Sailing in Different Sea State Conditions

Shipmasters must make several quick decisions with respect to the ship’s speed and heading
when new sea conditions approach. The implications for ship stability and risky situations are known
but there are no guides on how they should be addressed in this limited period of time. In the present
paper, and from three points of view, the ship’s rolling motion in the long-term domain is analysed.
Firstly, the ship’s behaviour after the influence of a single and external force was studied. Secondly,
the influence of successive regular beam seas, with resistance and at zero-speed conditions, was
analysed. Finally, the influence of wave direction on a ship sailing at non-zero speed was investigated.
Results showed that once five minutes elapse, the rolling angle tends to be null regardless of the ship’s
loading condition and that after a certain period of time, a coupling of the ship’s rolling frequency
with the waves’ period and angle amplitude occurs. This circumstance was noted after three minutes
for all of the ship loading conditions. Finally, novel guides for shipmasters in the form of 3D maps
and polar diagrams were proposed to improve the ship’s behaviour-altering navigational parameters
(heading and ship’s speed) when sailing in changing weather conditions. Therefore, for the three
approaches, the relevant results and novel mathematical relations of linear factors were obtained
which can be considered useful and applicable by the ship operators of most fishing and merchant
fleets (regardless of their sizes) when they are operating under normal loading conditions.