At first glance, the question of who has right of way in an overtaking situation at sea seems like a fairly straightforward question, but on closer scrutiny, there are ambiguities: For example if you are on a converging course with a boat slowly passing on your starboard bow are they overtaking or simply on a converging course? Who gives way?
The last place you want to start racking your brains about who is in the right is as you converge with a large tanker. With this in mind, Tim Bartlett's International Regulations for Preventing Collisions at Sea is an invaluable guide, breaking the text down into easy to understand sections and hopefully this excerpt on overtaking will clarify matters.
Overtaking is rule 13 in the IRPCS and overlaps nicely with rule 18 which outlines the responsibilities between vessels. These two rules, between them, set out a clear “pecking order”. In open water, you must keep out of the way of anyone that is higher in the pecking order than you:
Rule 13: Overtaking
(a) Notwithstanding anything contained in the Rules of Part B, Sections I and II, any vessel overtaking any other shall keep out of the way of the vessel being overtaken.
(b) A vessel shall be deemed to be overtaking when coming up with another vessel from a direction more than 22.5 degrees abaft her beam, that is, in such a position with reference to the vessel she is overtaking, that at night she would be able to see only the stern light of that vessel but neither of her sidelights.
(c) When a vessel is in any doubt as to whether she is overtaking another, she shall assume that this is the case and act accordingly.
(d) Any subsequent alteration of the bearing between the two vessels shall not make the overtaking vessel a crossing vessel within the meaning of these Rules or relieve her of the duty of keeping clear of the overtaken vessel until she is finally past and clear.
It is impossible to overstate the significance of the first dozen words of this rule, which set out its clear and absolute priority over all the other “steering and sailing” rules apart from Rule 19.
So far as the skippers of small craft are concerned, it means that a fast-moving sailing vessel may well be required to give way to a slow-moving motor boat – particularly in and around harbours, where powered craft are often subject to speed limits that sailors may not even know about.
The idea that the vessel which is overtaking has to keep clear is simple and familiar: it’s just the same on the road. Ships and boats, however, are not confined to narrow ribbons of tarmac, so at sea, you are regarded as “overtaking” if you are approaching another vessel from anywhere within an arc of 67.5° either side of dead astern.
Of course, as the overtaker pulls ahead, the relative bearing between the two vessels is bound to change, but paragraph (d) makes it clear that this doesn’t alter their relative status: the overtaking vessel is still obliged to keep clear of the other until she is “finally past and clear”.
This obligation does not give the vessel that is being overtaken the right to alter course into the path of the overtaker. Rule 17 imposes important responsibilities on the “stand-on” vessel, of which the most important is to maintain her course and speed.
This makes it important to get into the habit of looking astern before altering course. Motorcyclists call this quick look over the shoulder the “lifesaver”.
It is just as useful at sea.
A changing situation
The situation shown in fig 1. in which it appears that the overtaking vessel has ignored Rule 13: she was the overtaking vessel at first (B) but then, as she drew alongside the slower vessel (A), she altered course to port – presumably intending to pass ahead.
But suppose we had only seen the latter stages of the manoeuvre? In that case, as in fig 2, there’s no reason to assume that (B) was overtaking. Instead, she appears to be a “crossing vessel”, and (A) is the one that has to give way.
In spite of the Rule 13d, the fact that you may once have strayed into someone’s overtaking arc does not mean that you are bound to give way to them to the end of time!
The key factor is when the change from “overtaking” to “crossing” takes place, and how far apart the two vessels are at the time. Various court cases seem to suggest that if the change from overtaking to crossing takes place while the vessels are two or three miles apart, it should be regarded as a crossing situation, rather than as overtaking.
These legal precedents, however, concern ships, rather than small craft. For smaller or more manoeuvrable vessels the critical distance could be well under a mile, and might even reduce to a few boat lengths.
It is never enough to “just miss” another vessel. Rule 8 specifies that any action taken to avoid collision should result in the vessels passing “at a safe distance”.
This is particularly true when a large vessel is overtaking or being overtaken by a much smaller one, because it is under these circumstances that interaction – caused by pressure waves around their hulls – is likely to occur.
After the fatal collision between the dredger Bowbelle and the disco boat Marchioness, the Marine Accident Investigation Branch report said: “… when a relatively large ship is overtaking a smaller one, the latter will tend to sheer across the bow of the former. Where the two vessels are very close, the effect can be so great that the smaller vessel loses all control. It is highly likely that this effect was a cause, probably the major cause, of Marchioness sheering across the bow of Bowbelle”.
A much less subtle kind of interaction almost certainly accounted for the loss of the sailing yacht Ouzo and her three crew, after what was widely reported as a collision with the ferry Pride of Bilbao. The formal report, however, suggests that it was probably a very near miss, rather than a collision, and that Ouzo was swamped or capsized by the ferry’s wash.