Collision rules study overview

Apply COLREGs to meeting, crossing, overtaking and restricted visibility.

Practise observation and judgement using sailing scenarios. Interactive questions and your device-local progress load when JavaScript is available.

Study points

Rules 7, 15, 16 and 8 apply together: nearly constant bearing with decreasing range indicates risk; the vessel with the other on her starboard side keeps clear and, if circumstances admit, avoids crossing ahead. With the stated sea room, a substantial early alteration to pass astern is appropriate. Small successive alterations may be difficult to recognise, accelerating ahead creates an avoidable bow crossing, and a radio reply is not a prerequisite for action. Check that the manoeuvre actually produces a safe passing distance.
Rule 13 takes precedence over the usual sail-versus-power responsibilities in this encounter. Any vessel overtaking any other keeps out of the way. A later change in bearing does not turn the overtaker into a crossing vessel or end its duty: it must be finally past and clear, not merely have its bow ahead. The overtaken vessel still has lookout and collision-avoidance duties.
Rule 14(c) says that when in doubt whether a head-on situation exists, assume that it does and act accordingly. Under Rule 14(a), each power-driven vessel alters to starboard for port-to-port passing. Yawing or intermittent aspect observations are not a sound reason to select stand-on status or wait for certainty. Keep monitoring the other vessel and the effectiveness of your action.
Rule 3 defines a sailing vessel as one under sail whose propelling machinery is not being used. A yacht being propelled by its engine is power-driven even with sails set. Here the two power-driven vessels are crossing, so Rule 15 requires the yacht with the other on its starboard side to keep out of the way. Merely running an engine without using it for propulsion would not by itself change a sailing vessel’s classification.
Rule 9(a) requires keeping near the starboard outer limit only as safe and practicable; it does not require entering unsafe shallows. Under Rule 9(b), a vessel under 20 m must not impede a vessel that can safely navigate only in the channel. Rule 8(f) calls for early action to allow sufficient sea room. A passing agreement or a smaller size does not transfer that responsibility to the ship.
Rule 10(c) specifies a heading as nearly as practicable at right angles to the general direction of traffic flow, not a perpendicular course over ground. For north/south lanes an eastbound crossing heading is about 090° true. The tidal stream may make the ground track oblique, so plan the exit position and assess traffic separately. A perpendicular heading does not confer priority or remove the other collision-avoidance obligations.
Rule 17(a)(ii) permits the stand-on vessel to act alone as soon as the give-way vessel’s failure becomes apparent. That is distinct from Rule 17(b): when collision cannot be avoided by the give-way vessel alone, the stand-on vessel must take the action that best aids avoidance. In the earlier crossing intervention described here, Rule 17(c) says a power-driven vessel should, if circumstances admit, not alter to port for another power-driven vessel on her port side. Rule 17(d) keeps the original give-way duty in force.
Rule 6 requires a speed appropriate to actual circumstances, including traffic, manoeuvrability, stopping distance, sea state, depth and radar limitations. A local maximum is not a guarantee that its full value is safe. Neither an arbitrary half-limit nor waiting for a definite close encounter replaces assessment of detection and reaction margins. Reduce speed when necessary and continue reassessing as conditions change.

Educational revision only. Check current official rules, charts and publications before navigating.