Navigation

The direction in which a vessel’s head points as indicated by its magnetic compass. Compass heading includes the effect of the compass’s deviation and is converted to magnetic or true heading by applying deviation and variation with the correct signs. It is not necessarily the same as course over ground because of leeway and current.

The direction of the straight line between two positions actually reached by a vessel. It summarises the net direction of progress over the ground during the interval, regardless of steering changes between the fixes. It should be distinguished from heading, course steered and the intended track.

An angular area in which observation or a signal is obstructed or unreliable. Masts, sails, superstructure and equipment can create blind sectors for visual lookout, radar, lights or antennas. Their extent should be understood and compensated for by changing observation position, altering heading where safe or using additional sensors and lookouts.

The vessel required by the collision regulations to maintain course and speed during a specified encounter, initially. The obligation allows the give-way vessel to take predictable avoiding action, but it does not remove the need for a proper lookout or safe speed. The stand-on vessel may act when it becomes apparent the other vessel is…

A predetermined position or condition beyond which a manoeuvre or passage cannot be safely continued as planned. It provides an explicit trigger to stop, turn away or use a contingency before options become too limited. Abort points are particularly useful in pilotage, harbour approaches and close-quarters manoeuvring and should be linked to a practical escape…

The direction of an object measured clockwise from a vessel’s heading. It is normally expressed from 000° directly ahead through 090° on the starboard beam, 180° astern and 270° on the port beam. Adding relative bearing to the vessel’s true or magnetic heading, with the result reduced to 000°–359°, gives a bearing in the same…

A standard spoken instruction directing a vessel’s rudder or heading. Orders must be stated clearly, repeated by the helmsman and reported when achieved, using the terminology adopted aboard the vessel. The officer giving the order remains responsible for monitoring the vessel’s response and correcting for conditions such as wind, current and steering characteristics.

The spatial arrangement of navigation satellites relative to a receiver. Widely separated satellites generally provide a stronger position solution than satellites clustered in one part of the sky. Its effect is described by dilution-of-precision values, although signal blockage, multipath and other errors can still reduce accuracy.