This collision occurred within the pilot boarding area, just outside the dredged entrance/ exit channel to the port of Jebel Ali in the United Arab Emirates. Consequently, the claimant brought a collision action against the defendant that finally found her way to the UK Supreme Court, which had to deal with questions of real importance to mariners and to the effectiveness of the Collision Regulations in preventing, as far as possible, collisions at sea. As usual in such cases, the judge at first instance and the Court of Appeal sat with Nautical assessors (Elder Brethren | Trinity House); their role was to advise on matters of navigation and seamanship.
This post only refers to a part of the Judgement that helpfully explains the vessel’s heading, course and bearing. The following extract is taken verbatim from the Judgement.
“It will be necessary in what follows to make precise use of the words heading, course and bearing. None of them is expressly defined in the Collision Regulations. They are however words with a relatively settled meaning among mariners, as may be gathered from published nautical manuals and glossaries, and which it may be supposed that the Rules take for granted. The usage which follows has been checked with, and confirmed by, the Nautical Assessors, and is not a matter of controversy between the parties (see para ).
Sometimes heading and course are used interchangeably, as meaning the direction in which the vessel is being steered. But for present purposes we think it better (and the Nautical Assessors agree) to distinguish between them as follows. The heading of a vessel is the direction (expressed as a point or number of degrees on a compass) in which she is pointing at a particular moment in time. So, for example, a vessel is on a heading of north if a horizontal line projected from a compass on her centre point through her bow points north. Used in that sense, a vessel does not have to be moving to have a heading (see para ).
The course of a vessel is the direction, again expressed by reference to the points or degrees of a compass, in which she is moving. This may be through the water or over the ground. Course over the ground is sometimes called the course made good, so as to distinguish it from her course through the water. The judge uses course over the ground and course made good interchangeably. It is the course over the ground rather than the course through the water that matters for present purposes, as para 70 of the judge’s judgment makes clear. We use “course” in that sense. Where there is no wind or current the course of a vessel both through the water and over the ground may well be the same as her heading. She simply moves in the direction in which she is pointed. But this will not necessarily be so, as the Nautical Assessors have confirmed and the present case illustrates. Tidal stream, current, surface drift and wind, if present, will or may cause her course over the ground to be different from both her heading and her course through the water. Thus a vessel heading north in an easterly current will be on a course over the ground which is east of north, the amount of the easterly element being the product of the ratio between her speed (through the water) and the rate of the current. Broadly speaking, the slower the vessel’s speed and the faster the current, the greater will be the difference between her heading and her course over the ground….(see para )
Similarly, a wind may cause a vessel to make leeway, that is, to slide a little sideways through the water. This is almost invariably true of a sailing vessel (unless the wind is blowing from right astern) but can also be true of power-driven vessels such as high-sided container ships.. Since wind is described (unlike current) by reference to where it is coming from, a vessel heading north may have her course deflected east by a westerly wind. Leeway will produce a difference between a vessel’s heading and her course through the water. Sometimes leeway and current will act together to increase the difference between heading and course over the ground. Sometimes they may cancel each other out (see para ).
Course used as above may describe the direction of movement of a vessel at a particular point in time. More generally course may be used to describe the overall progress of the vessel over a period of time, which may accommodate changes in her heading and speed. As explained below a vessel may be said to maintain her course despite significant changes in heading and speed, measured at particular moments in time.. (see para )
The bearing of a vessel, as that concept is used in the Collision Regulations, is quite different from her heading or her course. Bearing is an expression with various maritime meanings, but for present purposes compass bearing is the meaning which matters. It is the direction in which one vessel appears when viewed from another at a particular moment in time, expressed again in terms of the points or degrees of a compass…As the Nautical Assessors have confirmed, the compass bearing of one vessel from another may generally be measured with reasonable precision, by day or by night by radar and, when the vessels are in sight of each other, assessed visually by using a compass (see para ).
Compass (or absolute) bearing is to be distinguished from relative bearing. This is the direction in which one vessel appears from the other, measured (usually now in degrees) as an angle from the viewing vessel’s heading, from zero (dead ahead) to 180 (dead astern)… (see para )”.
Case: Evergreen Marine (UK) Ltd v Nautical Challenge Ltd  UKSC 6 (19 February 2021)- See here: Evergreen Marine (UK) Ltd v Nautical Challenge Ltd  UKSC 6 (19 February 2021) (bailii.org)