COLREG Lights and Shapes: Trainer and Reference

A power-driven vessel underway shows a white masthead light (two if she is 50 m or more in length, the after one higher than the forward one), sidelights — green to starboard and red to port — and a white sternlight. A sailing vessel underway shows sidelights and a sternlight, but no masthead light. Pick a vessel in the reference and rotate it to see which lights are visible from each side.

Anchor lights — an all-round white light forward and a second one aft at a lower level if she is 50 m or more — plus two all-round red lights in a vertical line. By day, three balls. What sets her apart from a vessel not under command is precisely the anchor lights.

From her sidelights and the line of her masthead lights. If you see green, you are on her starboard side; red, on her port side; both, you are almost right ahead. On a vessel with two masthead lights the forward one is lower: if they are in line, she is heading toward you or away from you; if they are apart, she is crossing, and the lower light shows where her bow is.

From the geometry of the encounter. The target's course is derived from bearing, range and your own speed: if the bearing does not change and the range is closing, risk of collision exists under Rule 7, and Rules 13–18 apply. If the bearing changes appreciably, the vessels pass clear, and the correct answer is "no risk of collision".

A power-driven vessel making way — one prolonged blast every two minutes; stopped and making no way — two prolonged blasts. A vessel not under command, restricted in her ability to maneuver, constrained by her draft, under sail, fishing or towing — one prolonged followed by two short. At anchor — rapid ringing of the bell; aground — also three separate strokes before and after. You can listen to all of them in the Signals tab.

No, it is synthesized. It does keep what matters for identification: the length of a short and a prolonged blast under Rule 32 and the pitch set by vessel length in Annex III — lower on a larger vessel.

No, only the international COLREG-72. Inland waterways and small craft have their own rules with different lights and shapes (such as the US Inland Rules or CEVNI), and mixing them into one trainer would only cause confusion.

As a trainer, yes — that is what it is built for. As a source of the rules, no: the text of COLREG-72 and the official publications remain the only source. The simplifications here are stated openly: for example, a dredger's shapes on the side where you may pass are not drawn.