How Masthead Lights Can Help You Pass Ships at Night

Here’s another sailing tip from our friend Captain John at skippertips.com

Nightfall. Calm, peaceful, light winds from the southeast. Picture perfect with an awesome canopy of stars above your head. What was that? Just off the port bow? There it is again! Two white lights just over the horizon. A freighter? A super tanker? It’s too far away to see the side lights. It’s your call, skipper!

After sunset, will you be ready to identify ships that pass you in the night? How can you tell the difference between a meeting or crossing situation without sighting their sidelights?

During nighttime or periods of reduced visibility, ships are required to show white masthead lights. Large ships 50 meters or more in length must carry two white masthead lights, one forward and one aft and higher. You can use these two lights to assist you in determining risk of collision.

You will pick up a ship’s white masthead lights (also called “range lights”) at about twice the distance of red or green sidelights. Focus your attention on both white masthead lights to help you determine the ship’s direction of movement relative to your own boat. You will also need to shoot a series of bearings, called “drift bearings” to help you determine risk of collision (see below).

Can a Sailboat Become a “Power-Driven Vessel”?

Rule 3 (General Definitions): (b) The term “power-driven vessel” means any vessel propelled by machinery. (c)The term “sailing vessel” means any vessel under sail provided that propelling machinery, if fitted, is not being used.

As a sailing vessel (under sail alone), a power-driven vessel must stay clear of you. Common sense says that at all times when dealing with large ships at sea, you must avoid a close quarters situation if possible.

If you are under sail and power or power alone, you are considered a “power-driven vessel” in Rule 3. Turn on your masthead light in addition to side lights and stern light. As a power-driven vessel, you are on the same part of the “pecking order” as any other power-driven vessel (ships or small craft) and should maneuver as shown in the situations illustrated below.

Make Your Presence Known

Call the ship upon first sighting on the radio-channels 13, 16, (or channel 70 using the DSC function). Verify that they see you both visually and on radar. Do not assume that they can see your navigation lights. Make it clear to them whether you are under sail alone or under sail and power.

Make yourself highly visible to others at sea. Hoist radar reflectors high in the rigging and clear of sails or obstructions if possible. When in sight of another vessel, draw attention to yourself by shining a light on your sails or in the direction of the ship (but not into their pilot-house; this could “blind” the watchstanders).

Find Bearing Drift

When you first sight a ship on the horizon, take a series of compass bearings with a hand bearing compass onto some part of the vessel. For example, you could take a bearing to a white masthead light. A few minutes later, take another bearing to the same masthead light. Take a third bearing to the same masthead light a few minutes after the second bearing.

Determine whether those bearings are steady, or moving to the left or right. Steady bearings or slow bearing drift (moving at a slow rate to the right or left) indicate a high risk of collision. Fast changes in bearings, called fast or rapid bearing drift, indicates a minimum risk of collision. You want those bearings moving at a substantial pace. The faster the bearings change, the less the risk of collision between two vessels.

Note in some cases, bearings will change fast and risk of collision can be still be quite high. This can happen when you are close to another vessel, close to a large vessel, or close to a vessel engaged in towing.

Does Risk of Collision Exist?

Follow these examples that show you how to use bearing drift along with masthead lights in a meeting or crossing situation to help determine risk of collision. Note that the examples shown are for situations between power-driven vessels (see the referenced Rule in italics above the explanations below).

In this article, we will discuss power-driven vessels that are in sight and ahead of you or off your bow. “In sight” means that you can see them visually–not just on radar or AIS. Overtaking situations will be discussed in a future article.

Remember this is just one of many ways to determine if risk of collision exists. Use all means available, which includes radar, AIS, or other installed electronics along with visual bearings.

Ship Sighted Ahead – Masthead lights in line

International Rule 14(a)-(Head-On Situation): “When two power-driven vessel are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision each shall alter her course to starboard so that each shall pass on the port side of the other.”

Steady bearings, called steady bearing drift, with both masthead lights in line indicates a high risk of collision. If you have determined that risk of collision exists, you need to take action right now. It could take you a long time to clear out of the way of a fast moving ship. Alter course to starboard by a substantial amount (i.e. 90 degrees) and increase speed. Continue to shoot bearings. When the bearings show a rapid rate of drift, risk of collision will be at a minimum.

Ship Sighted off Our Starboard Bow

International Rule 15 -(Crossing Situation): When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel.

We sight this ship off of our starboard bow. Take a series of bearings as described earlier. Steady bearings or bearings that change at a slow pace indicate a high risk of collision. In a crossing situation with a ship off our starboard bow and if we have determined that risk of collision exists, we are the “give-way” vessel. That means we must change course, slow down, or stop to allow the ship to pass ahead of us.

Ship Sighted Off Our Port Bow

International Rule 15 -(Crossing Situation): When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel.

We sight this ship off of our port bow. Take a series of bearings as described earlier. Steady bearings or bearings that change at a slow pace indicate a high risk of collision. In a crossing situation with a ship off our port bow and if we have determined that risk of collision exists, we are the “stand-on” vessel and we must maintain course and speed. The other vessel will be the give-way vessel and should stay out of our way. But…

If it becomes apparent that the other vessel will not give way to allow you to cross ahead of them, then you must take action to avoid collision. Remember that all action to avoid collision must be substantial, so make any course or speed change large enough so as not to confuse the other vessel.

As a sailing skipper, you need to be able to determine within seconds how a ship will pass your small cruising sailboat at night. Use these simple methods to keep your sailing crew safe and sound when sailing near the busy shipping lanes of the world.

Captain John’s Sailing Tip
Choose a handbearing compass that can be read in the dark. This often requires a bright light to ‘charge’ the compass element that emits the light. Use a small flashlight, cupped in your hand to protect your night vision. Keep your handbearing compass on deck, ready for instant use.

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