Select Page

Most sailors today rely on GPS to find their way at sea. While GPS has helped to make finding your way at sea far easier than in the past, sailors still need to study charts before they embark on a passage and to use them en route to check and record their progress.

Failure to study and understand charts covering their proposed course could potentially put a sailor’s vessel in danger. For example, while a GPS might automatically pinpoint a sailor’s position it will not alert them to potential hazards along a route, such as shallow water or hazards beneath the surface, such as rocks.

Nautical charts are therefore 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:

  • Understand the symbols: Nautical charts are full of symbols that represent different features and hazards on the water and below its surface. Before you start using a chart, you should familiarise yourself with these symbols and what they mean. Most charts will have a key that explains the symbols used but there are also books and apps available that explain all the symbols and abbreviations used.
  • Determine the scale: The scale of a nautical chart refers to the ratio between the size of the chart and the size of the actual area it covers. For example, a chart with a scale of 1:50,000 means that one unit of distance on the chart represents 50,000 units of distance in the real world. Knowing the scale is important for calculating distances and planning your route.
  • Locate your position: Once you understand the symbols and scale, you can start to locate your position on the chart. Take bearings of visual landmarks and navigational aids such as buoys, lights and shapes to help determine where you are on the chart.
  • Plan your route: Nautical charts show depths, shoals, rocks and other hazards, so use this information to plan a safe route. Look for deep channels and avoid shallow areas. Be aware of navigational hazards such as rocks, reefs, and wrecks.
  • Check tides and currents: Nautical charts often include information about tides and currents, which can have a significant impact on your route and speed. Make sure to factor in these variables when planning your journey.

Overall, reading a nautical chart takes practice and familiarity with the symbols and conventions used. It’s important to approach chart reading with care and attention to detail to ensure a safe and successful voyage.

Variation

Variation is an important factor to consider when using a nautical chart for navigation. Variation is the difference between true north (which is the direction of the North Pole) and magnetic north (which is the direction of the earth’s magnetic field).

Magnetic north is not fixed and can change over time due to shifts in the earth’s magnetic field. This means that the magnetic north pole is constantly moving and can be different from true north at any given time and location.

When you’re using a compass for navigation, it’s important to account for this difference between true north and magnetic north. This is where variation comes in – variation is the angle between true north and magnetic north at a particular location.

On a nautical chart, variation is indicated by lines of isogonic variation, which show the difference between true north and magnetic north for a particular year. For example, a chart might show a line labeled “2023 Variation 6°W”, which means that the variation for that location in 2023 is 6 degrees west of true north.

To use a compass effectively for navigation, you need to adjust for variation by either adding or subtracting the appropriate amount from your heading. This will ensure that you are actually travelling in the direction you intend to go, even if your compass is pointing slightly off of true north due to magnetic variation.

It’s important to note that variation changes over time, so you should always consult the most up-to-date chart and navigation information to ensure accuracy in your calculations.

Compass deviation

Another factor that needs to be considered when using a compass for navigation is compass deviation. Compass deviation refers to the error in a magnetic compass caused by the magnetic fields of a vessel’s own structure and equipment. In other words, a compass will not necessarily point to true north or south because of the magnetic influence of the vessel itself.

This deviation can be caused by a variety of factors, such as the presence of steel or iron in the vessel’s hull, or by the presence of electrical equipment that creates a magnetic field. Deviation can also vary depending on the vessel’s orientation with respect to the Earth’s magnetic field, so it may be different when the vessel is heading north compared to when it is heading east or west.

To correct for compass deviation, a vessel will typically use a compass deviation card or table that lists the deviation values for different headings. This information can be obtained by swinging the compass, which involves turning the vessel in a complete circle while comparing the compass reading to the known true heading at each point. Once the deviation is known, the compass readings can be adjusted accordingly to provide more accurate navigation.

Summary

These are just a few reminders of how to read a nautical chart. There is no mention of the traditional methods and instruments used to plot a course. It is also a reminder that it is not prudent to place blind faith in electronics without having a good understanding of navigation skills, as well as seamanship and meteorology.

 

Take a look here at our Chart Symbol apps:

 

For all sailors who use paper nautical charts or electronic ones – with these apps you’ll have all the chart explanations to hand!

Boating App – Chart Symbols & Abbreviations

   

Boating App – Electronic Chart Symbols (ECDIS)

  

 

 

 

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.

Weather forecasting resources and tips

All competent sailors need to have a good basic understanding of how to interpret a weather forecast. They also need to be able to interpret the actual conditions they are experiencing.

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.

Antifouling for leisure boats – Part 3

Antifouling is one of the least pleasant boat maintenance jobs to do, but it has to be done. The very worst job of all is removing the old antifouling as this can get seriously messy and is very hard work.

How to operate a winch

Winches are drum shaped mechanical devices used to handle halyards, sheets and control lines. One of the important crew...

Five dangers a vessel may encounter at sea

What are the main dangers a vessel may face at sea and what should skippers do to reduce the risk of these happening?

Narrowboating on the Kennet and Avon Canal

A recently cancelled sailing event I was due to take part in left us with a free weekend in the diary. Given that my wife and I were celebrating a bumper wedding anniversary and the weather forecast was for fine weather, we decided to hunt around for a last minute canal holiday.

How to predict wind direction and strength by reading a weather chart

Weather charts, also known as surface pressure or synoptic charts, contain a lot of information that helps weather...

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.

Saildrive maintenance

There are less maintenance tasks to carry out on a saildrive transmission than on a traditional inboard shaft drive system with its associated stern gear. However, there are a few critical things that require maintenance, as recommended in detail by the engine manufacturers, and should be adhered to.

Sailing at the touch of a button

Easier and more controlled sail handling can also be achieved by powering up a furling mast. I came across some interesting solutions at the Southampton Boat Show this week on the Selden Mast stand, where they were running demos of their E40i electric winch and SMF furling system.

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.

First aid at sea – four common emergencies

In this blog we look at what to do in the event of a crew member choking, drowning, or suffering from hypothermia or fatigue. Knowing how to cope with them could well save a life, while not knowing could result in an avoidable tragedy.

Boat batteries

Under-sized battery banks are one of the key factors behind power failure at sea, as well as the premature failure of batteries, so make sure that your boat battery measures up to the use you want to put it to.

Understanding your boat’s compass

Article submitted by Mike Rossiter, Certificated Compass Adjuster. Since the magnetic compass was first used by the Chinese...

How to improve a yacht’s upwind performance

There are several ways to improve the upwind performance of a sailing yacht. Read on for some useful tips including headsail reefing, heavy weather jibs and motor sailing.

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).

How to tackle osmosis

Many owners of old GRP boats live in fear of osmosis, but what exactly is osmosis and what can be done about it? Osmosis comes about...

Essential Knots: Round turn and two half hitches

Essential Knots: Round turn and two half hitches Use: Tying a rope to a pole or a ring. Step 1. Pass the end around the object. Step 2....

Boat Improvements

My Boat - practical improvements Author - Mike Rossiter Most boat owners who have had their craft for any length of time will have made what they...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 6 – Communications

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the sixth of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

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.

Engine failure at sea – keeping the boat safe

If the engine stops when you are underway, or your have to shut it down when a warning buzzer sounds, you also need to make sure the boat remains safe. It’s important therefore to recognise situations in which the boat would be immediately put in danger if the engine were to fail.

Boat Engine Safety Checks

  Boat Engine Safety Checks Every skipper needs to make regular essential boat engine safety checks. Below you will...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 7 – Motivation

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the seventh of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.