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!

Learn ColRegs: Traffic Separation Schemes

Learn ColRegs Rule 10: Traffic Separation Schemes. (c) A vessel shall, so far as practicable, avoid crossing traffic lanes...

Dripless shaft seals

Dripless shaft seals are designed to completely stop water from entering a boat’s hull via the stern tube. There are two main types of dripless seals known as face seals and lip seals which many boat manufacturers now fit to production boats.

Seasickness – how can you prevent it?

Seasickness is a common problem at sea and affects both seasoned sailors and novices. What are the causes and symptoms of seasickness?...

Hull inspection – the annual checks

With the boat ashore for the winter it is time to do a hull inspection - the annual checks. Are there any scratches and chips in the...

How diesel engines work

The basic principle of a diesel engine is less complex than that of a petrol engine. No spark plug or ignition system is needed, making the basic diesel engine a comparatively straightforward system that results in fewer faults and has lower maintenance costs than a petrol engine.

Understanding your mast and rigging

The rig of a sailing boat is put under huge stresses and strains so it is important for inspections of a yacht's spars and rigging to be...

Marine engine oil system maintenance

The regular maintenance of a marine diesel is key to preventing engine failure at sea. This means doing regular checks of the fuel, cooling, electrical and oil systems.

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.

Capsize – understanding the risks

A skipper should know how their boat will cope with rough seas. By working within known limits and understanding the risks,...

Cleaning & polishing painted topsides

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.

Propeller care and maintenance

Propellers are complicated and repairs should be done by specialists but owners can carry out checks and some routine maintenance themselves when the boat is in the boatyard. A propeller is critical to a boat’s performance, fuel consumption and ride, so it makes sense to keep a propeller in good working order.

Boat ownership

Owning a boat is a big commitment that should bring no end of satisfaction for the owner as well as the owner's family and friends. In...

Weather forecasting tips

Most weather forecasts present a general picture of what to expect in your area over a given period of time. We rely on such...

Understanding boat engines

Irrespective of what kind of engine a boat is equipped with and who does the work, the regular care and maintenance of a marine engine is essential. The most common cause of marine engine failure is widely known to be lack of maintenance.

Leaking decks

Leaking decks are perceived as a nuisance by some boat owners, but if leaks are ignored a much more serious situation may well be developing, especially in the case of boats with balsa or plywood deck cores. So deck leaks do need to be investigated and dealt with.

Wooden Hull Repairs

While wooden boat hull maintenance is mostly straightforward, it is always a good idea to take expert advice on any repair job needed doing to a wooden boat, unless you have done the job before and know what you are doing.

Sterndrive maintenance

Sterndrives are a popular form of propulsion in the powerboat market, but require a fair amount of care and maintenance. The main factors to be aware of are salt water corrosion, lubrication and regular inspection of the bellows, the condition of which is vital to prevent water from entering into the hull.

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...

Boat Handling – anchoring

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

Rewiring a boat – overcoming the challenges involved

Skippers need to have a basic knowledge of boat electrics, to avoid potential problems and to be able to solve them when they happen.

Boating Rules of the Road – International ColRegs

    International ColRegs Rule 7: Risk of Collision Anyone who is responsible for a vessel at sea, from the...

ColRegs when sailing single handed

  Don’t neglect the Colregs when sailing single handed Sailing single-handed represents several challenges for skippers, not least how to...

A five day sailing cruise of the Solent, UK

Welcome to our virtual Solent sailing cruise – a five day sail in the south of England from Bosham Quay in Chichester...

Pleasure craft safety equipment recommendations

Safety equipment is an important part of boat preparation and it is advisable for all pleasure craft skippers to check their vessel is...

Keel design – options to consider when choosing a yacht

Keel design is constantly evolving and nowhere is this more apparent than in modern racing yachts such as the Imoca Open 60...