KVR in practice: How motorboat skippers can recognise the risk of collision
Sven M. Rutter
· 25.09.2026
Whether another vessel is merely passing by or becomes a potential collision risk is not determined at the moment of first visual contact. Motorboat operators must assess the bearing, rate of approach and available on-board technology together before the obligations to give way or hold course come into effect. This allows the course or speed to be adjusted clearly and in good time.
During a night-time voyage on the Baltic Sea, the motorboat is travelling at a steady speed across calm waters. Apart from the starry sky, the only thing visible ahead on the port side is the green navigation light of another vessel. At the helm, several questions immediately spring to mind: what type of vessel is it, how fast is it approaching, and which right-of-way rule might apply? However, before the skipper decides on a change of course or adjustment to the vessel’s speed, a more fundamental question must be answered: is there actually a risk of a collision?
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When the duty to give way and the duty to maintain course apply
As mentioned in the article “KVR for motorboat operators: Why right of way alone does not prevent collisions” As explained, the international rules for the prevention of collisions do not recognise the concept of right of way. They allocate responsibilities and distinguish between vessels required to give way and those required to maintain their course.
These roles do not arise automatically as soon as another boat or vessel becomes visible from the helm. Even when two motorboats encounter each other, the allocation of roles only applies once the vessels have approached each other to such an extent that there is a risk of collision.
Vertical bearing as a warning signal at the helm
Rule 7 of the KVR requires every vessel to use all available means to ascertain whether there is a risk of collision. The prescribed lookout is therefore not sufficient on its own. If another vessel is sighted, the skipper must observe its subsequent movements and assess the situation.
An important indicator is the compass bearing. If the bearing of an approaching vessel does not change noticeably, there is generally a risk of collision. From the perspective of one’s own vessel, the other vessel then remains in the same direction whilst the distance between them decreases.
For the motorboat operator, the first question is therefore: Is the green light getting closer without veering off to the side? The possible allocation of responsibilities can already be considered mentally. However, the duty to give way or the duty to maintain course only become relevant if there is actually a risk of collision.
If several position lights or targets are visible, the approaches must be prioritised. The decisive factors are which vessel is likely to result in a critical passing distance and how much time remains until the closest approach.
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Check the bearing, don’t just guess it
From the helm, an initial bearing can be taken, for example, using a fixed edge of the windscreen, an instrument rack or another fixed point on board. A marine telescope with a bearing compass provides more reliable readings. Its magnification makes it easier to identify a distinct bearing marker on a larger vessel, such as the bridge, bow, funnel or navigation light.
If I take a bearing on this feature at 300 degrees the first time and at 310 degrees a few minutes later, this indicates that the danger has temporarily passed. If, on the other hand, the bearing hardly changes and the vessel is simultaneously getting larger, 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 little 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 with 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. It also provides clear guidance in cases of uncertainty: where in doubt, one must always assume a ‘worst-case scenario’, i.e. an imminent risk of collision. If, in the example given, the green light fluctuates so much that a reliable bearing cannot be determined, this must not be taken as a signal to relax. If the situation remains unclear, the motorboat operator must assume there is a risk of collision and remain ready to act accordingly.
Radar displays the distance and time remaining
Rule 7 explicitly mentions radar as an available aid. As the relevant driving rule applies in all visibility conditions, the radar system can also be used to monitor traffic conditions even when visibility is good.
Its advantage lies in its predictive capability. The analysis shows how close two vehicles are expected to come to one another and how much time remains until that point. The Closest Point of Approach, or CPA for short, refers to the minimum expected passing distance. The Time to Closest Point of Approach, or TCPA for short, indicates the time remaining until this approach.
Where there are multiple targets, these values can be used to identify which encounter requires attention first. A vehicle with a critical CPA and a short TCPA takes priority in terms of observation and situation assessment.
This analysis can be carried out visually or using a MARPA function. However, in conditions of good visibility, it does not replace visual observation, as the vehicle type cannot be reliably determined from the radar echo alone. BOOTE provides detailed operating guidance in its advice section “How to get the most out of your on-board radar”.
CPA and TCPA
Calculating the CPA and TCPA makes it easier to assess potential collision risks. This involves forecasting the future approach to another vessel based on the movement data observed by radar or AIS. The diagram shows a projection of the situation at 10:00 for the following 15 minutes. Accordingly, the closest approach does not occur 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).
Radar does not take the pressure off the skipper
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 recreational 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 the relevant 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.
Supplement AIS data, scrutinise data critically
AIS provides additional information about traffic in the vicinity and, depending on the device configuration, also displays CPA and TCPA. The system is not explicitly mentioned in the KVR. Its data must therefore not be used as the sole basis for assessing an approach.
Only vessels that transmit AIS data and are received by the user’s own device appear on the display. Furthermore, the position, vessel status and other details may be out of date or incorrect. Particularly in the case of fast motorboats, longer update intervals may result in a position that has already changed being displayed with a time lag.
Nevertheless, AIS remains a valuable addition. It makes it easier to assess a vessel’s size and movement and can facilitate direct contact. However, whether a boat reported as a sailing vessel is actually under sail can only be determined by observation. The single green light in the opening example must therefore still be classified on the basis of visual observation.
Act early and maintain a safe passing 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, ‘lead to 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 just past the stern would therefore not be behaviour in accordance with the rules. Passing close to 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. In open waters, however, one should give vessels maintaining their course as wide a berth as possible. An 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 continuous CPA alarm. Everyone should ask themselves whether this can be recognised beyond doubt by the other vessel as a manoeuvre to give way.
Change your route or cancel your journey
Similarly, one should refrain from ‘edging in’ by making constant, small adjustments to course or speed. Confusion can also arise if the boat taking evasive action yaws sharply in rough seas or regularly luffs up and bear away 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 could not be sure whether it was a small sailing boat or a large four-masted barque.
However, a large-scale change of course requires sufficient space. Alternatively, in accordance with Rule 8, a complete stop might need to be considered. I have often temporarily put 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, you must put yourself in the position of the vessel maintaining its course: from their perspective, when would the situation be definitively resolved?
If the party required to give way fails to react
Under Rule 17, the vessel maintaining course must first maintain its course and speed. This obligation is intended to make the skipper’s behaviour predictable for the vessel required to give way. It does not cease simply because the motorboat skipper suspects that the other vessel is reacting too late or inadequately.
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 making a call via marine radio. If the other vessel still fails to respond, the vessel on the course may take action itself to defuse the situation. This is also known as the ‘last-minute manoeuvre’. However, the vessel on course is not obliged to do so – unless the two vessels come so close together 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 stage, a collision would still occur. In that case, the vessel on course is obliged to take evasive action themselves – using what is known as the last-moment manoeuvre.
These vehicles need space
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 do not grant these vehicles any special rights – they merely impose obligations on other vehicles. Thus, vehicles whose safe passage must not be obstructed 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 recreational 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 ensure there is no ambiguity in this regard. After all, even the mere possibility of a collision would trigger the 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 ability to do so. 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).
Book recommendations
Rules for the prevention of collisions explains the international rules for the prevention of collisions at sea in a format designed for use on board. Numerous illustrations and clear summaries help readers to understand the meaning of lights, visual signals and the basic rules of way.
KVR. SeeSchStrO brings together the latest versions of the collision prevention regulations, the Maritime Waterways Regulations and the Ems Estuary Navigation Regulations. This volume is aimed at water sports enthusiasts who wish to consult the legal framework governing German maritime waterways.