Reading ship lights at night: how to practise what you learned for the exam

Most people learn navigation lights from diagrams in a book, pass the exam, and forget them. Then comes the first night at sea, with a red light, two whites and a confusing background of shore lights. The diagram did not prepare you for that moment, because a diagram shows you the answer, and at sea you have to find it.

Ask three questions, in this order

1. Which way is she going? A red sidelight means you see her port side. Green, her starboard side. Both together, she is heading straight at you. A white stern light on its own, you are looking at her from behind.
2. What is she? One or two masthead lights: a power-driven vessel. Extra lights show a special job, as in the table below.
3. What does it mean for me? Is the bearing changing? If it stays steady and she is getting closer, there is a risk of collision. Who gives way?

The sectors you need to know

On a large ship, the two masthead lights tell you a lot. The aft one is higher. If they are nearly in line, she is pointing at you. As they open, she is showing you her side, and you can read which way she is going from which side the higher light moves to.

The common combinations

How to make it stick

There are two steps here: recognising combinations, then doing it in context.

Step 1: drill recognition. Rules 23–31 of the COLREG exercises contain 23 recognition quizzes, drawn as the vessel looks at night: power-driven, sailing, towing, fishing and trawling, not under command, restricted in her ability to manoeuvre, CBD, pilot, anchored, aground and others. One free exercise is open in each of the seven modules, and all of them come with the simulator subscription.

Step 2: meet them when you are not expecting it. During THE BALTIC LAP a ship or two will pass your boat. At night, what can you tell from her lights alone? Do the three questions before you check her on the radar or chart. In Free Mode you can go further, with COLREG traffic that gives way as the Rules say, on a sea where navigation lights come on at sunset with the real sun.

The lights in the simulator follow the rule's sectors, so a ship's sidelight disappears as she turns away and her stern light appears. The lights, the radar picture and the chart look and behave much as they do at sea. So when you first step aboard, you won't be starting from zero, and it will show.

Be honest about the limits

A screen is clean. A real night has shore lights behind the ship, spray on your glasses, a boat moving under you and tiredness. Real sailors also make mistakes about what they see, so treat your first reading as a guess and confirm it. If in doubt, assume the worst and act early. In THE BALTIC LAP, ships keep clear and boats do not collide, so use it for identifying; practise the avoiding action in the COLREG exercises.

For the full rule text, see our article on Rule 23.

FAQ

Why does a sailing boat show no masthead light?

Because a masthead light means engine power. A sailing vessel that starts her engine becomes a power-driven vessel and has to show one.

How do I remember all the combinations?

Learn the logic first: which way, then what. Then drill a few at a time. The old memory rhymes help for some, such as "red over green, sailing machine" for the optional masthead lights of a sailing vessel.

Related reading

• Radar, AIS and chart: build the picture before you go aboard
• Think like a skipper: how an online regatta becomes virtual practice for real decisions
• What does a skipper actually think about at sea? A beginner's guide
• COLREG simulator — 54 collision-avoidance exercises on a radar, AIS and bridge-view console, in the browser
• Online sailing regatta simulator — THE BALTIC LAP, a one-design race round the whole Baltic in real wind, in your browser
• All articles · Open the simulator

Boat types are described generically; SkipperCheck is not affiliated with any boat builder or class association.