KVR explains: When the obligation to give way and the obligation to keep to one’s course come into effect

A balmy summer’s night on the Baltic Sea; the gentle breeze carries the sailing boat along almost silently on a half-wind course. Apart from the magnificent starry sky, only a single green light can be seen ahead on the port side. A harmless neighbour or a potential adversary? For experienced skippers, the ‘rules engine’ in their heads kicks in automatically in such situations: What type of vessel? From which direction? Which rule applies? Who must give way? In fact, however, there is another question that comes first: Is there even a risk of collision?

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Probability of a hit

As in the first part on Responsibility and presumed right of way under the KVR As explained, the International Regulations for Preventing Collisions at Sea (KVR) do not recognise the concept of right of way. They only set out obligations and provide for a division of roles amongst the vehicles involved, distinguishing between road users who are obliged to give way and those who are obliged to maintain their course.

A common misunderstanding is to assume, as soon as another vessel comes into view, that this automatically triggers the allocation of roles. However, if, as in the opening example, two sailing boats or two motorboats encounter one another, an additional condition must be met: the allocation of roles under the KVR only applies once they are ‘approaching one another in such a way that there is a risk of collision’.

​According to the KVR, the risk of collision begins with the bearing measurement

That is why Rule 7 of the KVR requires every vessel to first check ‘by all available means’ whether there is a risk of collision. This goes beyond simply keeping a lookout, as required by Rule 5: as soon as another vessel is sighted, an analysis of the situation is also required. Rule 7 also specifies what needs to be checked in this context, as it states that a risk of collision must always be assumed whenever the compass bearing of an approaching vessel does not change noticeably – in short, when the bearing remains constant.

The first question is therefore: is the green light actually getting closer, and is its bearing remaining constant? Of course, in practice, it never hurts to run through a possible evasion scenario in your head, just in case. However, the two vessels are only obliged to give way or to maintain their course once the bearing remains constant. If the position lights of several vessels are visible, this gives rise to corresponding priorities: Which situation could become critical? Which of them is approaching the fastest?

Useful tools

Some people make do with taking a bearing using a railing post or similar object. A marine telescope fitted with a bearing compass provides more reliable results. Compared to a hand-held bearing compass, it offers the advantage of magnification: this means that, with larger ships, a specific feature can be used as a bearing mark – such as the bridge, the bow, the funnel or a navigation light.

If I take a bearing on this marker at 300 degrees the first time and at 310 degrees a few minutes later, this indicates that there is no immediate danger. If, on the other hand, the bearing hardly changes and the ship appears to be getting larger at the same time, I must assume a potential collision course. In heavy seas, I take my cue from the range within which the bearing fluctuates. If it is initially between 305 and 310 degrees and, a short while later, between 310 and 315 degrees, I can breathe a sigh of relief for the time being.

Of course, the other vessel should still be kept under observation. Particularly in the case of very large vessels and those that are close by, a bearing that appears to be drifting away can give a false sense of security, as Rule 7 also points out. In cases of uncertainty, it also provides a clear guideline: In case of doubt, one must always assume a ‘worst-case scenario’, i.e. an imminent risk of collision. If, for example, the green light in the opening example were to swing back and forth sharply and elude a reliable bearing, the roles would still be assigned accordingly.

Keep an eye on everything

Rule 7 cites radar as a further aid. It is set out in Section I of the Rules on Manoeuvring and Navigation, which, according to Rule 4, applies in all visibility conditions. The use of radar is therefore also intended for use even in the best visibility conditions. This raises the question: what can radar, a lookout and a bearing compass not also achieve in good visibility?

The answer is: forward projection. How close are we likely to get to the other vessel, and how much time remains until then? By analysing the radar image, it is possible to determine the so-called Closest Point of Approach (CPA) and the Time to Closest Point of Approach (TCPA) – that is, the point of closest approach between the two vehicles and the time until the minimum passing distance is reached. The TCPA is calculated from the distance and approach speed and, in turn, determines the priorities: which vehicle with a critical CPA requires immediate action?

This evaluation procedure is known as plotting and is explicitly mentioned in Rule 7. Whether this is done manually or using an electronic MARPA function (Mini Automatic Radar Plotting Aid) is irrelevant. Especially as this section does not concern a radar-based evasive manoeuvre. Provided visibility is not impaired, evasive action is generally taken based on visual observation. After all, the radar cannot identify the type of vessel involved.

​CPA and TCPA

Calculating the CPA and TCPA makes it easier to assess the risk of a potential collision. This involves projecting the future approach to another vessel based on the movement data observed by radar or AIS. The diagram shows a forecast of the situation at 10:00 for the following 15 minutes. Accordingly, the closest approach does not occur only when the leading line is crossed at 10:15, but after just 11 minutes (TCPA). The minimum passing distance is 0.6 nautical miles (CPA).

Lookout vs. screen

So does the radar always have to be running? According to Rule 7, its purpose is to provide ‘early warning’. It can also be used to clarify ambiguous situations. For the early warning function, however, the radar’s reliable target detection would need to extend significantly further than the lookout can see. This is by no means always the case on pleasure craft. Moreover, with their limited resolution and screen size, basic yacht radar systems do not always provide a more reliable analysis than visual observation.

In short: it depends on the circumstances in each individual case. Especially as there is no general obligation for pleasure craft to carry radar equipment that defines corresponding minimum requirements. Anyone who is unsure whether their own radar system is providing reliable results should, in unclear situations, assume there is a risk of collision straight away. After all, Rule 7 also states that no conclusions should be drawn from inadequate radar information.

The situation is different for some ‘large vessels’, which, due to their restricted bridge visibility, are reliant on additional radar image analysis even in the best of weather. When dealing with such vessels, it is essential to ensure your own visibility by fitting a suitable reflector and/or an AIS transceiver, whatever the visibility conditions.

Unclear data situation

In addition to radar, the Automatic Identification System (AIS) also provides information on surrounding traffic – including CPA and TCPA. Yet the KVR make no mention of it whatsoever. This may be because, with the AIS, there is always some residual doubt as to the timeliness and accuracy of the information available.

Furthermore, only vessels that transmit the relevant data appear on the AIS – and that is by no means all of them. Nevertheless, the AIS can be helpful in collision avoidance, for example when assessing a vessel’s size and manoeuvrability. Furthermore, in unclear situations, it provides the opportunity to make direct contact.

Incidentally, reservations are warranted even regarding the reported vessel type. A sailing yacht that identifies itself as a ‘Sailing Vessel’ in the AIS is not necessarily actually sailing. This can only be confirmed by visual observation: the single green light visible on the Baltic Sea at night definitely belongs to a sailing yacht – even if it appears on the AIS as a pleasure craft.

Keep your distance

The correct course of action in the event of a risk of collision is set out in Rules 8, 16 and 17. According to Rule 16, the vessel obliged to give way must ‘act as early as possible and decisively’. In practice, this means: do not wait to see how the situation develops – but take evasive action immediately as soon as it is clear that you are obliged to do so. This is particularly important as an evasive manoeuvre should not only prevent a collision but, according to Rule 8, ‘result in a safe passing distance’. This requirement goes significantly further – it means that a vessel obliged to give way must, as a general rule, keep clear of the immediate vicinity of the other vessel. Skirting closely past the stern would therefore not constitute behaviour in accordance with the rules. Passing just in front of the bow would also contravene the duty of care set out in Rule 2.

The point at which a CPA is deemed to constitute a critical proximity depends, in turn, on the individual circumstances. In some sections of the sailing area, a certain degree of proximity cannot always be entirely avoided. Out on the open sea, however, one should give vessels maintaining their course as wide a berth as possible. A evasive manoeuvre must also be so distinct that it is immediately and unambiguously recognisable by the other vessel ‘visually or by radar’. If a vessel obliged to give way is merely heading towards the stern of another vessel, it continues to present its bow – or, at night, its two side lights – to that vessel. At the same time, the radar would issue a persistent CPA alarm. Everyone should ask themselves whether this can be recognised beyond doubt by the other vessel as a manoeuvre to give way.

Play or Pause

Similarly, one should refrain from ‘edging in’ by making constant, small adjustments to course or speed. Ambiguities can also arise if the evading boat yaws sharply in rough seas or regularly luffs up and falls off in gusty winds. As a general rule: it is better to keep too much distance than too little. After all, if you saw a single green light in the dark of night, you couldn’t be sure whether you were dealing with a small sailing boat or a large four-masted barque.

However, a wide-ranging change of course requires sufficient clear space. Alternatively, in accordance with Rule 8, a complete stop might need to be considered. I have often temporarily turned my sailing yacht into the wind in order to fulfil my duty to give way. This is not an unusual manoeuvre, particularly on busy waterways such as the Lower Elbe. Incidentally, the duty to give way only ends once the other vessel is ‘definitively past and clear’. To determine this, one must put oneself in the position of the vessel maintaining its course: from their perspective, when would the situation be definitively resolved?

At the last minute

Meanwhile, under Rule 17, the vessel holding the right of way is obliged to maintain its course and speed. As explained in the first episode, it does not, therefore, have a ‘free pass’. There is only one exception to this obligation: if it becomes clear that the vessel required to give way is failing to do so.

A mere assumption is not sufficient for this. Clarity can be achieved by alerting the vessel in question to its duty to give way. This can be done by means of an acoustic signal – at least five short blasts in succession – or by a call via marine radio. If the other vessel still fails to respond, the vessel keeping the course may take action itself to defuse the situation. This is also known as a last-minute manoeuvre. However, the vessel on course is not obliged to do so – unless the two vessels come so close to one another that the vessel obliged to give way can no longer effectively prevent the collision on its own. Even if they were to take evasive action at this point, a collision would still occur. In such cases, the vessel in command is obliged to take evasive action themselves – using what is known as the last-moment manoeuvre.

The so-called 'Premier League'

In addition to vehicles required to give way and those maintaining their course, Rule 8f introduces a further special category: vehicles whose safe passage must not be obstructed. Some place them at the very top of the hierarchy. In fact, however, the KVR does not grant these vehicles any special rights – it merely imposes obligations on other vehicles. Thus, vehicles whose safe passage must not be impeded remain obliged to follow the KVR’s rules on giving way if there is a risk of collision. However, other vehicles are required to behave in such a way that a division of roles between those maintaining their course and those obliged to give way does not arise in the first place.

If, as a pleasure craft, you encounter such a vessel, there is therefore no need to first assess whether there is a risk of collision – in such cases, you must always give way and keep clear. And you should not allow any ambiguity to arise in this regard. After all, even the mere possibility of a collision would trigger the appropriate allocation of roles. You should therefore, for example, not sail in front of such vessels – not even when tacking. Similarly, you should avoid overtaking too closely, as this too could trigger the allocation of roles.

According to Section 18d, this category includes all vessels with limited draught. No other vessel may obstruct their safe passage, unless it is itself unable to manoeuvre or is restricted in its manoeuvrability. Sailing vessels and motorboats under 20 metres in length must also not obstruct the safe passage of ships in narrow fairways – nor that of motorised vessels using a traffic separation scheme (TSS).