Chapter 9: The Tensions in the Rules, and Why They’re There
A reader coming to the Rules closely for the first time will sooner or later catch them apparently contradicting themselves. One rule seems to demand what another forbids. A threshold that decides who must give way is never actually stated. An obligation written as an absolute turns out to bend in practice. The natural reaction is to assume the drafters were careless. They were not. The collision regulations are among the most heavily litigated and carefully revised legal instruments in existence, and the tensions in them have survived a century and a half of amendment because they are doing a job. They are not all of one kind. A few are genuine contradictions, where two rules pull against each other over the same water. More often they are undefined thresholds the text deliberately refuses to fix, or hard structural edges where one regime hands over abruptly to another. This chapter argues that almost all of them, whatever their kind, are deliberate places where the drafters declined to prescribe a fixed answer and handed the decision to the mariner instead. It then works through the most important of them.
Why a careful text leaves gaps on purpose
The drafters could have closed most of these gaps with a number. They could have defined a head-on situation as a meeting within a stated number of degrees, fixed a close-quarters situation at a stated range, or set the moment a stand-on vessel must act at a stated distance. They chose not to, and the reason is the same one that runs through the whole instrument. A fixed threshold that is safe for a manoeuvrable warship is dangerous for a loaded tanker, and one that is prudent for a tanker is absurdly early for a patrol boat. Any number the drafters wrote down would be wrong for most of the vessels most of the time. So at each point where the right answer genuinely depends on the vessels and the circumstances, the Rules deliberately stop short of an answer and require judgement, bounded by the purpose of the Rules and held to the standard of good seamanship that Chapter 10 sets out. These tensions are not holes in the text. They are the text declining to pretend it can do the mariner’s thinking for him.
What follows are the tensions an OOW is most likely to meet, with the Rules in conflict, the gap each leaves, and how it is resolved in practice. None of them has a tidy textual answer, and that is deliberate.
The nearly reciprocal problem: head-on or crossing?
The sharpest tension is between Rule 14, the head-on situation, and Rule 15, the crossing situation, because misclassifying the encounter is itself dangerous. Rule 14 applies when two power-driven vessels meet on reciprocal or nearly reciprocal courses, and requires both to alter to starboard for a port-to-port passing (MISCPUB 0127, Rule 14(a)). Rule 15 applies when they are crossing, and burdens only one of them, leaving the other to stand on. The boundary between “nearly reciprocal” and “crossing” is nowhere defined. Rule 14(b) offers a visual test, that the situation is deemed to exist when a vessel sees the other ahead or nearly ahead, by night the masthead lights in a line or nearly in a line and/or both sidelights (MISCPUB 0127, Rule 14(b)). But “nearly in a line” is itself undefined, and because each sidelight shows across an arc that reaches the bow, both sidelights are visible across a spread of approaches that extends into what might geometrically be a crossing.
The danger is real and not theoretical. If one master reads the meeting as head-on and alters to starboard while the other reads it as crossing and stands on, their two correct-feeling decisions combine into a collision. The Rules resolve the ambiguity not by defining the boundary but by removing the doubt: when a vessel is in any doubt as to whether a head-on situation exists, she shall assume that it does and act accordingly (MISCPUB 0127, Rule 14(c)). The conservative response is always to treat it as head-on and turn to starboard. The cost of getting this wrong is on the record. In Sea Star–Horta Barbosa, 1976, two vessels on reciprocal courses were closing to pass starboard to starboard when the Sea Star made a late, substantial alteration to starboard. She sank with loss of life and was found mainly to blame for attempting to cross ahead at close range (cited in Cockcroft & Lameijer, 7th ed, comment on Rule 14). The lesson the case teaches is exactly Rule 14(c): resolve the doubt early and in favour of the port-to-port passing, not late and against it.
When an overtaking becomes a crossing, and when it does not
Rule 13 settles the overtaking relationship with unusual firmness: a subsequent alteration of bearing does not make the overtaking vessel a crossing vessel or relieve her of the duty to keep clear until she is finally past and clear (MISCPUB 0127, Rule 13(d)). The classification, once it attaches, is locked. The tension arises at the edges of that lock. If a faster vessel comes up from astern, draws ahead, and the geometry then shifts so that she is crossing the bow of the vessel she passed, can a fresh crossing situation under Rule 15 begin? The answer turns on whether risk of collision ever existed during the overtaking geometry. If it did, Rule 13(d) holds the vessels in an overtaking relationship until they are finally past and clear. If it never did, the encounter rules never engaged, the vessels merely happened to lie in an overtaking aspect at distance, and a crossing situation can develop fresh once risk of collision arises in the new geometry. In Auriga–Manuel Campos, 1977, the vessels began in an overtaking aspect but on courses diverging by several degrees, shaping to pass about three miles off, so no risk of collision existed during the overtaking phase. The crossing rule was held to apply to the later close-quarters situation (cited in Cockcroft & Lameijer, 7th ed, comment on Rule 13). The resolution is supplied by case law because the text alone does not say it.
How close is “coming up with”?
Rule 13 carries a quieter ambiguity. Unlike Rules 14 and 15, it contains no “so as to involve risk of collision” trigger. On its face, any vessel coming up from more than 22.5 degrees abaft the beam is overtaking, with no distance qualifier at all (MISCPUB 0127, Rule 13(b)). Read to its literal limit, a vessel forty miles astern on a fractionally faster course would already be the overtaking vessel and the ship ahead already the stand-on vessel, which is plainly unworkable. The Court of Appeal closed the gap in Olympian–Nowy Sacz, 1977, by reading the words “coming up with” as carrying an implied requirement of proximity: the overtaking rule begins to operate before there is risk of collision, but only once it can properly be said that one vessel is coming up with the other, which does not apply at any distance however great (cited in Cockcroft & Lameijer, 7th ed, comment on Rule 13). So Rule 13 engages earlier than the risk-of-collision rules but not infinitely early, settling at a working proximity rather than a fixed range. The exact distance, predictably, is left to judgement and to the speed differential involved.
“Finally past and clear” has no number
The phrase that ends an encounter, finally past and clear, appears in Rules 8(d) and 13(d) and is left entirely qualitative. “Finally” demands that the encounter be genuinely over with no realistic prospect of re-engagement. “Past” demands that the geometric relationship has resolved and the other vessel is well abaft. “Clear” demands that there is enough separation that no reasonable mariner would still treat a collision-avoidance relationship as running. No distance is attached to any of the three, and deliberately so, because any fixed figure would be dangerous for one vessel and absurd for another. The practical catch is that the threshold can only be judged with certainty after the fact. A master who treats the encounter as finished and alters across the other vessel, but is later found not to have been finally past and clear, was in breach from the moment she altered. The defence is conservatism: do not treat an encounter as over until it unmistakably is.
An unqualified “shall”: course and speed through a long overtake
When a vessel is being overtaken she is the stand-on vessel, and Rule 17(a)(i) requires her to keep her course and speed, an instruction written as an unqualified “shall” (MISCPUB 0127, Rule 17(a)(i)). In a crossing this obligation lasts minutes. In a long overtake between vessels of similar speed it could run for an hour, during which the stand-on vessel may have entirely legitimate reasons to alter: a waypoint to round, a channel to enter, a current to allow for. The text provides no navigational exception. The tension resolves through three sources read together. Rule 2(a) means a vessel cannot slavishly hold course into danger merely to comply with Rule 17, since that would itself be a neglect of good seamanship. Rule 13(d) protects her, because the overtaking vessel remains burdened even if the stand-on vessel alters. And the courts have never read the obligation as a literal freeze: in Windsor–Roanoke, 1908, a stand-on vessel that stopped her engines to embark a pilot was held justified despite the duty to keep course and speed (cited in Cockcroft & Lameijer, 7th ed, comment on Rule 17). What the rule actually demands is predictability within the collision-avoidance relationship, not an absolute ban on all navigation.
DRAFTING ISSUE: a navigational alteration that creates new danger
The gap the text leaves open is what happens if the stand-on vessel’s legitimate navigational alteration brings her closer to the overtaking vessel. Rule 13(d) keeps the overtaker burdened, but Rule 2(a) could fix the stand-on vessel with fault for creating the danger. The text allocates no clear answer, and a court would likely apportion blame. The practical protection is to make any such alteration early, make it obvious, and where possible signal it, so that the overtaking vessel can accommodate it.
When may the stand-on vessel act, and when must she?
Rule 17 builds in a three-step escalation, and the triggers between the steps are judgement calls with no quantitative criteria. The stand-on vessel keeps her course and speed under 17(a)(i). She may take action by her own manoeuvre as soon as it becomes apparent that the give-way vessel is not taking appropriate action, under 17(a)(ii). And she shall take such action as will best avoid collision when she finds herself so close that the give-way vessel’s action alone cannot prevent it, under 17(b) (MISCPUB 0127, Rule 17). The danger is in the gap between “may act” and “shall act.” A stand-on vessel that acts too early under 17(a)(ii) can confuse a give-way vessel whose own manoeuvre is just developing. One that waits too long sails past the 17(b) threshold and arrives in extremis with no sea room left. Neither trigger is a number, and that is the difficulty rather than an oversight, because the right moment depends on the closing speed, the room available and the manoeuvrability of both ships. Even the action permitted is constrained: a power-driven vessel acting under 17(a)(ii) in a crossing should not, if circumstances admit, alter to port for a vessel on her own port side (MISCPUB 0127, Rule 17(c)). That both vessels can end up at fault, the one for failing to give way and the other for failing to act in time, is on the record in Statue of Liberty–Andulo, 1970, where blame fell on both the give-way and the stand-on vessel (cited in Cockcroft & Lameijer, 7th ed).
Two regimes over one waterway: Rule 9 and Rule 10
Rule 9 governs conduct in narrow channels and Rule 10 conduct in traffic separation schemes, and both can apply to the same stretch of water at once. In the ordinary case they pull the same way, but they conflict at the edges. For a crossing vessel, Rule 10(c) directs a crossing as near to a right angle as practicable, while Rule 9(d) says she must not cross if to do so impedes a vessel that can only navigate within the channel, and the two do not say which yields. For a vessel joining or leaving, Rule 10(b) calls for as small an angle as practicable, while Rule 9(a) calls for keeping to the starboard side, and depending on which side she enters from, those can point in different directions. The Rules supply no explicit hierarchy between the two. In practice the conflict is resolved below the level of the Convention, by local regulation, by VTS direction, and by the IMO routeing publications, with the routeing measure generally taking priority for lane discipline while Rule 9’s keep-to-starboard governs conduct within the lane. This is one place where the resolution is convention rather than text, and an OOW needs to know that the answer lives in the local instructions, not in the COLREGs alone.
The instantaneous switch: out of the fog and into Section II
Chapter 5 set out that the visibility state decides which rules govern. The drafting tension that creates is at the boundary. In restricted visibility Rule 19 governs and there is no stand-on or give-way vessel. The moment visual contact is established the encounter falls under Section II, with its give-way and stand-on roles, and that switch is instantaneous (MISCPUB 0127, Rule 19(a); and see Chapter 5). There is no graduated transition and no grace period. A vessel that has been manoeuvring lawfully under Rule 19 can find herself, at the instant the fog thins, the newly designated give-way vessel in a crossing with almost no time or sea room to discharge the obligation, and possibly already heading the wrong way for it. The Rules contain no provision to soften this. What they do instead is hedge against it in advance: Rule 19(d) directs a vessel taking action against a radar contact to avoid, so far as possible, an alteration of course to port for a vessel forward of the beam (MISCPUB 0127, Rule 19(d)(i)). That restriction exists precisely so that a vessel is less likely to be caught, when the fog lifts, in the unfavourable port-to-port-crossing geometry the sudden transition could otherwise produce.
Overtaking in restricted visibility: the regime that disappears
There is a further consequence of the visibility-state structure that an OOW must see clearly, because it takes away a tool he leans on heavily in clear weather. The whole overtaking regime of Rule 13, the firm allocation that the overtaking vessel keeps clear, the lock of Rule 13(d), and the overtaken vessel’s entitlement to stand on, belongs to Section II and applies only to vessels in sight of one another (MISCPUB 0127, Rule 11 and Rule 13(a)). In restricted visibility it does not exist. BR45 states the point flatly: Rule 13 does not apply in restricted visibility, where Rule 19 is paramount (BR45 Vol 4, para 1006a).
So when you come up on a slower vessel from astern in fog, holding her only on radar, there is no overtaking rule governing the closing. No vessel is obliged to keep clear and none is entitled to hold her course. Both ships are governed independently by Rule 19, each required to take avoiding action in ample time on her own assessment of the contact (MISCPUB 0127, Rule 19(d)). The overtaken vessel may never know she is being overtaken at all, since she sees only a contact closing from astern, and she carries no stand-on duty that would make her behaviour predictable to you. The clean, one-sided overtaking relationship that clear visibility hands you disappears exactly when reduced visibility makes the closing hardest to read, which is why this is a genuine problem and not a technicality.
The Rules acknowledge overtaking geometry in restricted visibility in only one place, and it is easy to miss. Rule 19(d) tells a vessel taking action against a radar contact to avoid, so far as possible, an alteration of course to port for a vessel forward of the beam, but it carves out one exception: “other than for a vessel being overtaken” (MISCPUB 0127, Rule 19(d)(i)). That is the text conceding that overtaking is the single case where a port alteration toward a forward contact is sound, and permitting it. But it is a permission about which way to turn, not a restoration of the overtaking regime. The clear allocation of responsibility that Rule 13 provides in sight has no equivalent in fog. In restricted visibility, overtaking is just another closing that both vessels must resolve independently under Rule 19.
How to resolve a contradiction: structure, definitions, purpose
When you meet one of these tensions on watch, the way out is not to hunt for a rule that settles it, because often none does. It is to apply, in order, the three things Part I has been building. First the structure, from Chapter 5: establish which Part and Section govern, because that alone disposes of many apparent conflicts, as the fog-transition case shows. Then the definitions, from Chapter 7: pin down the state each vessel is in, because most ambiguities are really classification questions in disguise. Then the purpose, from Chapter 1: ask what predictability requires here, and choose the action that the other bridge is most likely to read correctly. Behind all three stands Rule 2 and the standard of good seamanship from Chapter 10, which is the measure your judgement will be held to when the text has run out.
This is why this chapter and Chapter 10 are two halves of one idea. These tensions are the places where the Rules deliberately hand you the decision. Good seamanship is what they expect you to do with it. An officer who has only memorised the text arrives at exactly these points with nothing to apply, because the text has, on purpose, given the problem back to him. An officer who understands why the gaps are there meets them already knowing they are the moments the whole instrument was pointing at.
A short worked case: the meeting that could be either
You are closing another power-driven vessel at night, fine on your own port bow, her range decreasing and her bearing barely changing. By her lights you can see both her sidelights, but she seems a touch to starboard of dead ahead, so a starboard-to-starboard passing looks tempting and a crossing reading would let you stand on. Apply the method. The structure puts you in Part B, Section II, vessels in sight. The definitions ask whether this is a head-on or a crossing, and the honest answer is that it is genuinely ambiguous, both sidelights showing on a near-reciprocal course. That ambiguity is itself the trigger: Rule 14(c) requires that in any doubt you assume a head-on situation exists (MISCPUB 0127, Rule 14(c)). Purpose confirms it, because the port-to-port turn to starboard is the manoeuvre the other bridge is most likely to expect and read. So you alter boldly to starboard in good time for a port-to-port passing, and you do not reach for the starboard-to-starboard passing that Sea Star reached for too late. The contradiction did not have a textual answer that named a boundary. It had a method, and the method resolved it.
See also: Ch 1 (predictability as the test of last resort), Ch 5 (the structure that disposes of many apparent conflicts), Ch 7 (the definitions that most ambiguities really turn on), Ch 10 (Rule 2 and good seamanship, the standard your judgement is held to), and Part II, where each of these tensions is taken up again at the rule that creates it.