Action to Avoid Collision & Rules of Thumb

Rule 8 — Action to avoid collision

Any action shall be positive, made in ample time and with due regard to the observance of good seamanship.

Alterations of course and/or speed shall be large enough to be readily apparent to another vessel observing visually or by radar. A succession of small alterations should be avoided.

If there is sufficient sea room, alteration of course alone may be the most effective action, provided it is made in good time, is substantial and does not result in another close-quarters situation.

Action to avoid collision shall result in passing at a safe distance; its effectiveness shall be checked until the other vessel is finally past and clear.

Rules of thumb

Alter course by at least 30° (60°–90° at close range) so the alteration is unmistakable on the other vessel's radar.

Take action by 6–8 nm in open water; never let a developing situation run inside 2 nm unresolved.

Alter to starboard by preference. Avoid altering to port for a vessel on your own port side (Rule 17(c)).

If in doubt, slow down. A reduction of speed or taking all way off is always available and is explicitly sanctioned by Rule 8(e).

Aim to open the bearing: watch the target's relative motion line move clear astern of own ship on the radar.