Understanding navigation lights

Navigation lights are divided into two sets. The first set define the type and size of the vessel and are ALWAYS present, whatever type of work the vessel was built for. The second set of lights defines the work the vessel undertakes or temporary factors affecting its manoeuvrability such as being in a channel.

The first set is designed to allow you to determine which way the vessel is facing and whether it is very large. To do this, they are designed in to be seen in certain directions only e.g. the arc of visibility of the white light at the stern of the vessel should only be visibly to someone approaching the vessel from behind so the light is constructed so to can only be seen if you are well aft of the vessel.

The second set tell you what the vessel is currently doing and these lights are designed to be seen from all angles i.e. they are all round lights. (There are one or two exceptions and I will come to those later).

So, to begin to understand what you are seeing at night, begin by learning the first set of lights as these are by far the most important. (It is good to know that a vessel is temporarily constrained by her draught because she is in a channel, but first I want to know whether she is moving and which way she is pointing).

Is she moving?

Fig 1. A single all round white light is used to indicate that vessel of less than 50 metres is at anchor i.e. not moving.

Single white light for vessel of less than 50m at anchor.

Fig 2. Two all round white lights indicate the same thing but for a vessel of more than 50 metres.

Two white light for vessel of 50m or more at anchor.

Fig 3. A vessel that is not at anchor may still not be moving, or making way as its called, and in this case it will have its port, starboard and stern navigation lights on. No other navigation lights will be on. So, a vessel you can see that is showing a single green light is a vessel not at anchor, so defined as underway, but not moving or making way and you are looking at its starboard side and it is pointing to your right. If you see a single red light, then she is pointing the other way.

Vessel underway but not moving.

If you see a single white light, then you cannot tell much because that may be a stern light of a stationary vessel, or a moving vessel or, indeed, an anchor light or the only light on a boat of less than 7 metres doing anything it pleases at any speed.

Vessel actually moving

Vessels show one or two steaming lights to indicate that they are making way. One light is mandatory for vessels under 50m and two for vessels over 50m. Vessels less than 50m may show two if they wish. So vessels that are actually moving will show their port and starboard navigation lights, a stern light and one or two steaming lights, the furthest toward the stern of the boat being higher than the second.

Because they are navigation lights, they all have restricted arcs of visibility as follows:
  1. Port and starboard lights, red and green 112.5° Visible from dead ahead through to 22.5° astern past 90°
  2. Stern light, white - 135° (Making it visible up to 67.5° either side of the middle of the stern.
  3. Towing light at the stern, yellow 135° as per the normal stern light.
  4. Steaming light, white - 225°, 112.5° either side of centre line.

It is these visibility restrictions that make it possible for you to determine what angle you are to the vessel. If you can see a white light high up and a green and red light on either side, then the vessel is both moving and coming towards you (Fig.4).

The following diagrams show what you would see from each angle:

Fig 4.Vessel heading right for you head on.

Vessel underway coming towards you head on.

Fig 5. Vessel heading in same direction.

Vessel underway in front of you and heading in the same direction (or at anchor).

Fig 6. Vessel approaching, presenting their port side to you (moving right to left).

Vessel approaching, presenting their port side to you, moving right to left.

Fig 7. Vessel approaching, presenting their starboard side to you (moving left to right).

Vessel approaching, presenting their starboard side to you, moving left to right.)

Fig 8. Vessel over 50m approaching, presenting their starboard side to you. Vessels over 50 m have to display two white lights, the stern one being higher.

Vessel over 50m approaching, presenting their starboard side to you.

Fig 9. Vessel over 50m approaching you head on.

Vessel over 50m approaching you head on.

Fig 10. Vessel over 50m approaching, presenting their port side.

Vessel over 50m approaching, presenting their port side.

Having covered the basics of vessels at anchor or underway, the second thing you need to know is … is she doing anything.

Working Lights

Vessels engaged in work at sea such as fishing, dredging, towing, piloting and even mine clearance use special lights at night to let you know the extra navigational hazard they represent to other shipping.

Vessels that are constrained in some other way, such as by draft or being aground also show lights to let you know their situation.

These lights are additional to the compliment of standard lights each vessel must show. In many cases, they and the standard navigation lights are shown together. In some, however, the steaming light may be turned off while the special lights are on. Examples of this are trawling, fishing and pilot duties.

Fig 11 details the more common working light sets and their types:

Common navigation working lights.

Remember, these are working or situational lights they are on in specific circumstances. For example, the trawler will only have its trawling lights on when it is actually trawling. At all other times it will be lit as a normal vessel according to its size.

Using Fig 11 above, you can assemble the lighting for each type of work yourself. To get you started, here are some examples:

Fig 12. A vessel engaged in trawling:

Working navigation lights for a vessel engaged in trawling.

In this case, the 225 primary steaming light has been turned off and the two all round trawling lights turned on.

Fig 13. A vessel engaged in fishing:

Working navigation lights for a vessel engaged in fishing.

Fishing boats will even tell you if they have nets out more than 150m, with an additional white light on the working side and with two additional all round white lights on the mast for shooting or a white and a red for hauling.

Fig 14. A pilot boat:

Working navigation lights for a pilot vessel.

Fig 15. A more complex example a vessel constrained by its draft, coming down a channel towards you.

Working navigation lights for a vessel constrained by draft , coming down a channel.

Fig 16. Or this one this vessel is restricted in its ability to manoeuvre because it is towing another vessel:

Working navigation lights for a vessel restricted in its ability to manoeuvre because it is towing another vessel.

Fig 17. Last example This vessel is aground so it is showing its anchor lights (it is not making way nor underway) and is unable to change its situation:

Vessel aground and unable to change its situation.

In conclusion

Trying to remember by rote all the various navigation light combinations from cards works for some. An alternative approach is to remember the underlying logic of combining type of vessel, movement and working navigational lights and working out from first principles what is the meaning behind them.

You can build your own lights so have a go. Try a vessel under 50m towing another vessel over 200m, seen from astern and then in front.

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