Select Page

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

Navigating at night is made possible through an assortment of navigation aids, both ancient and modern. Lights are arguably the most important of these. Therefore, navigators need to be able identify the different types of light and what they signify. 

Electronic instruments help pinpoint a boat’s position, heading and speed. However, in order to be able to steer a safe and accurate passage, navigators must look out for and recognise the lights of navigation marks, beacons and lighthouses along their route.

How are lights identified?

Trying to identify every light you see can be difficult, especially when entering a harbour at night. In order to help with identification, each type has three main features:

  • Colour – green, red and white are most common. Yellow, blue, orange and purple are also sometimes used. 
  • Character – the rhythm of the light, or the flashing pattern it makes. 
  • Period – the length of time the light’s flashing sequence takes in seconds.

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.

Light characteristics

Unless you are unfortunately colour blind, identifying the colour of lights is not too challenging. However, identifying a light’s character and the length of time its flashing sequence takes requires good night vision and concentration.

There are a number of light patterns which are used. Navigators need to learn the different types and their chart abbreviations in order to interpret charts correctly and to recognise lights. They include:

  • Fixed (F) – a single steady light. Often 2 together.
  • Occulting (Oc) – long periods of light with short periods of darkness. This has the effect of making the periods of darkness seem like flashes. 
  • Isophase (Iso) – equal periods of light and dark.
  • Flashing (Fl) – short periods of light with long periods of darkness. Eg Fl(3) flashes in groups of three and then a period of darkness.
  • Quick (Q) – quick flashes of light varying from 50 to 300 flashes per minute.
  • Alternating (Al) – a light with different colours of alternating light. Eg (Al RG) alternating red and green lights.
  • Morse code (Mo) – lights that flash a Morse code letter.

Tip: 

Time several light sequences with a stopwatch to confirm you have identified a light correctly.

Classes of lights and their abbreviations

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.

Light abbreviations

Charts, almanacs and pilot guides use abbreviations to describe lights A typical light characteristic, including its height above sea level and range is condensed into a few letters and numbers. Here is an example together with its meaning explained:

Fl(4) WRG 20s 23m 25M

FL(4)   Character of light: regularly repeating a group of 4 flashes.

WRG   Colours of light: white, red and green. If no colour is given then the light is white.

20s   Period of time taken to exhibit one full sequence: 20 seconds.

23m   Height of light above MHWS: 23 metres.

25M   Luminous range  the distance at which the light can be seen: 25 nautical 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.

Happy boating and stay safe on the water!

Stress cracks on GRP boats

It is quite common to find cracks in the gelcoat when inspecting the deck and superstructure of a GRP boat. It is important to differentiate between a gelcoat crack and a scratch.

Safety at sea principles

Safety at sea is not as simple as just spending money adding shiny new emergency equipment such as liferafts, danbuoys, distress flares, EPIRBs and so on.

Seized fixings and fastenings

Maintaining a boat can be a rewarding experience but at times it can also be frustrating. A prime example of this is when you come across a seized fixing or fastening that refuses to budge. Read our tips on how to release and fix them:

Avoiding personal dangers at sea

In order to stay safe at sea, we need to know the risks we are facing and to be aware of any personal dangers we could possibly encounter. Here are six of the most common potential dangers individual crew members should be aware of.

Learn ColRegs: Traffic Separation Schemes

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

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...

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.

How to Avoid Collisions At Sea With The ColRegs

      Every Skipper Needs Accurate Knowledge of the IRPCS ColRegs As a responsible skipper it is every skipper’s duty to learn and apply the IRPCS...

How to read nautical charts

Whilst most sailors today rely on GPS to find their way at sea, nautical charts are a crucial tool for any sailor to navigate safely and effectively. Here is a reminder of some of the basic steps involved in reading a nautical chart:

Sailing Safely at Night – Best Practice

Sailing at night can be a magical experience – the peaceful solitude, starry skies, and gentle lapping of waves create an unforgettable atmosphere. However, nighttime sailing also presents unique challenges and risks that require careful preparation and vigilance. This comprehensive guide will cover essential safety practices to ensure your nocturnal nautical adventures are both enjoyable and secure.

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...

Boat interior varnishing

Most boat interiors have a combination of varnished and painted surfaces including solid wooden joinery, plywood laminates with thin hardwood veneers and glass reinforced plastic. When making your assessment of what you are going to do, bear in mind that the varnishing process consumes a lot of time, especially if the existing surfaces are in poor shape.

Right boat vs Wrong boat – Over 30 Ways to Cut the Cost of Your Sailing and Cruising

Sailing and cruising offer unparalleled freedom and adventure, but they can quickly become costly. Fortunately, there are numerous strategies to help you enjoy the open water without breaking the bank. Here are over 30 practical ways to cut your sailing and cruising costs.

Care of boat batteries

Boat batteries need to be kept properly charged, which means never allowing the batteries to discharge below 50 per cent of their total charge. As well as the batteries themselves, keeping a boat’s charging systems in good shape will also help to keep batteries topped up to a higher level of charge.

Rudders and steering systems – Part 1

Rudders and steering systems. A rudder is one of the most critical parts of a boat. Rudder failure is a common occurrence on neglected or overworked boats and a very unpleasant and potentially dangerous thing to happen when you are out at sea.

Safety Equipment Checklist for Boats

Safety Equipment Checklist for Boats   Liferaft line attached The liferaft will not work unless the trigger line is...

Stern gear maintenance

The stern gear of a boat needs to be checked carefully when the boat is ashore as this is something that can only be done when it is out of the water. The same applies for any maintenance and repairs that may need doing, so it is best to check it all over as soon after an end of season lift out as possible.

Boat engine cooling systems

Some boat engine breakdowns are unavoidable but those caused by lack of maintenance or regular checks can be avoided. Failure to maintain an engine’s cooling system is a well known example of this, so it is well worth spending time checking over the cooling system both when the boat is ashore and afloat.

Fixing position at sea using traditional methods

This post looks at some traditional methods used for fixing a vessel’s position at sea, within sight of land. Electronic fixes using chart plotters are very straightforward to record, but if for some reason a vessel’s electronics are faulty it is essential that a skipper knows how to use traditional methods.

Essential boat engine checklist

Boat engine checklist Engine oil level check Even if you have checked it previously, confirming the engine oil level is up...

Preparing for sailboat cruising

Preparing for a sailing trip entails a lot of planning. In this blog, we take a look at some of the many safety aspects that a skipper needs to consider before heading off on a cruise.

Going aground – what to do if it happens to you

When a yacht runs aground, it can be a stressful situation, especially on a falling tide in an exposed position with a swell running. There are several steps you can take to address the situation in order to ensure the safety of your vessel and its occupants. Here are some tips should this happen to you.

Sailing into fog – being prepared and staying safe

Most skippers will sensibly delay their departure, if fog is forecast. However, if fog begins to form when you are at sea it is important to be prepared, and know what precautions to take, to help make your vessel detectable or visible in fog and keep the crew safe.

Boat decks and superstructure

The deck of a boat is constantly exposed to the elements and should be inspected on an annual basis. Particular attention needs to be given to the overall condition of deck fittings such as the stanchions, cleats and chainplates.

Winch Servicing

It is not essential to service the winches when a boat is ashore, but if time allows I prefer to do this maintenance job when the boat...