Select Page

Sector lights, directional lights and leading lights guide vessels safely through hazardous waters or narrow channels at night. These lights are used when approaching or leaving harbours and are marked on charts and in nautical almanacs. How do they differ from one another?

A typical sector light has three arcs of light coloured red, white and green. In order to stay safe, as a vessel approaches the light it has to stay in the white sector. If the vessel moves into the red or green sectors, then this indicates that the vessel is no longer in the safe channel. If the vessel is within the IALA A system, it needs to alter course as follows:

  • red sector – indicates the port side of the channel. The vessel needs to steer to starboard to return to the white sector.
  • green sector – indicates the starboard side of the channel. The vessel needs to steer to port to return to the white sector.
  • white sector – indicates safe water.

Sector lights guide vessels through hazardous channels or into harbours with narrow entrances. The boat shown here would only be able to see a white light, as it is in the white sector. 

Sector lights are shown on charts with their light characteristics. The light characteristics in the diagram above are IsoWRG3s9m8M. This means: isophase, white, red and green, flashing every 3 seconds, height 9 metres, range 8 miles. 

Learn all about buoyage and lights in our reference app IALA Buoys & Lights at Sea for all navigators at sea. The app includes a quiz to test yourself.

Directional lights

Directional lights are similar to sector lights. A directional light guides a vessel into harbour in a very narrow channel. There is less margin for error than with a sector light as the channel is so narrow. The light beam is usually flanked by darkness rather than coloured light sectors, as is the case with sector lights.

The correct angle of approach for a directional light is given as a compass bearing on charts. Unlike sector lights, directional lights are marked on charts as single, unbroken lines, with the angle also marked on the line.

Once the navigator has seen the light, they are on the correct bearing and are safe to enter the harbour.

The directional light in the diagram here flashes on a bearing of 220.5º. Its light characteristic is Fl(2) 5s 10m 12M. This means it flashes twice every 5 seconds, is at a height of 10 metres above MHWS and can be seen from a distance of 12 miles. 

Learn all about buoyage and lights in our reference app IALA Buoys & Lights at Sea for all navigators at sea. The app includes a quiz to test yourself.

Leading lights

Leading lights are pairs of beacons that help navigators keep on the correct line of approach into harbour. They work in the same way as leading marks do during the day, where two day marks or shore features give the correct course, if lined up. 

While leading lights are excellent aids to night time navigation, it is important you have identified the  correct two lights to line up, which is not always easy.  

Leading lights show the safe line to take. Here, you are too far to port if the lower light moves to the right and so you need to steer to starboard. If the light moves to the left, you need to steer to port.

Learn all about buoyage and lights in our reference app IALA Buoys & Lights at Sea for all navigators at sea.  The app includes a quiz to test yourself.

Happy boating and stay safe on the water!

Essential Knots: Figure of eight

Essential Knots: Figure of eight Use: Stopper knot, prevents a rope from being pulled through a hole e.g. through a block or...

Repairing chips and dings in gelcoat

The gelcoat topsides of a GRP boat can be pampered and restored to their former glory relatively easily when it is ashore. Gelcoat is only a very thin outer layer of the hull, often less than 1mm thick, so you should avoid cleaning it with highly abrasive cleaners, or an-ything that could potentially damage its surface.

Tacking a sailing boat

Tacking is the sailing manoeuvre used to change a boat's direction through an oncoming wind. Tacking a sailing boat calls...

Points of Sailing

The course on which a boat is sailing can be described by its angle to the wind, not to be confused with its compass...

Essential Boat Safety Briefing

Skippers Responsibilities Skippers are obliged to give a safety briefing to the crew even if they are a regular crew. At...

ColRegs Rule 14 – Head-on Situation

  ColRegs Rule 14: Head-on Situation (a) When two power-driven vessels are meeting on reciprocal or nearly reciprocal...

Gybing a sailing boat

Gybing is the sailing manoeuvre used to change a boat's direction through a following wind. As with the tacking manoeuvre,...

Keel maintenance and Repair – Part 2

If you have ever witnessed a boat colliding with a rock or other submerged obstacle you will know that there is an almighty thump and the whole boat shakes and judders. While such hard groundings seldom result in catastrophic keel failure, something has to give and even the sturdiest keels can easily be damaged by such an impact.

Essential Knots: Clove hitch

Essential Knots: Clove hitch Use: Tying a rope to posts, bollards, rings or a guardrail. Step 1. Make a turn around the object and lay...

Galvanic and electrolytic corrosion

Galvanic corrosion is an electrochemical reaction between two or more different metals, in the presence of an electrolyte (note salt water is a good electrolyte).

Safety Briefings – leave nothing to chance

Before giving your crew a safety briefing, it is worth considering the specific circumstances of the planned trip, the...

The give-way hierarchy at sea – who gives way to whom?

Whatever their size or type, all skippers have a responsibility to avoid collisions with other boats at sea.  It is...

Light characteristics – how do navigators identify lights at night?

How do navigators identify the different types of light around our coasts at night and what are their characteristics?Navigating at...

Antifouling for leisure boats – Part 4

Applying antifouling. Antifouling is best applied on a dry, calm day. It is best to apply the antifouling in the middle of the day to ensure the hull is dry and as warm as possible.

You Need To Understand The IRPCS ColRegs To Pass Your Yachtmaster, Master of Yachts and Coxswain Certificate of Competence

IRPCS ColRegs Rules of the Road at Sea and Yachtmaster Learning, understanding and remembering the International Regulations...

Essential yacht tender safety for skippers and crew

Essential yacht tender safety - the dangers inherent in using a dinghy to get ashore from a moored or anchored yacht are all...

Rudders and steering systems – Part 3

In the third of our three blog articles on rudders and steering systems, we look at how to replace rudder bearings and repair a water-saturated core.

Essential Knots: Reef knot

Essential Knots: Reef knot Use: Tying two ends of rope together, often used for tying up a bundle of loose sail around the boom. Step...

Boat Engine Failure – what to check

Engine failure If your engine fails or is overheating there are a number of things to check immediately: • Air filter...

Peer to Peer yacht charter – How can you monetize your boat?

There is a growing trend in peer to peer yacht charter. How does it work? People already rent rooms, cars and bikes from one...

Distress flares – which flare, how & when to use?

How to use distress flares at sea Flares should be kept in a waterproof container in an easily accessible location such as a...

Understanding marine sealants & adhesives

Sealants, adhesives and adhesive sealantsThere is a bewildering variety of sealants, adhesives and even adhesive sealants available for...

Steel hull maintenance

A steel boat owner’s biggest enemy is corrosion. You don’t have to worry about osmosis or rotting timbers, instead rust is the number one issue that will keep you awake at night.

Boat maintenance log

Keeping a boat maintenance log is an ideal way of reminding owners what needs to be done to a boat and when. Read on for some tips,...

Boat Handling – anchoring

Anchoring your yacht or motorboat Anchoring is one of the most important boat handling skills. If you can set an anchor...