Introduction

Coastal and Offshore Navigation is designed to raise the game of a basic inshore pilot to a fully fledged offshore navigator capable of handling any passage short of an ocean crossing. The book follows on from its companion work Inshore Navigation whose brief is to prepare a navigator for short inshore passages executed in daylight. That definition sits comfortably with the RYA ‘Day Skipper’ and ‘Basic Navigation’ syllabi. The outcome of this volume is navigation at RYA/MCA ‘Yachtmaster Offshore/Coastal Skipper’ level. If you have no interest in certification, rest assured that it contains what you need to stay safe using techniques from non-electronic essentials through to the latest in electronic chart plotters.

Because this is a stand-alone unit, there is some repetition of core material already discussed in the previous book. Readers who have recently taken a Day Skipper qualification or who have started out with the inshore book will find this a reassuring recap. For the rest, that information will serve to confirm the ageless foundations of marine navigation in a world where change is everywhere.

Tom Cunliffe

1   Charts, publications and essential chartwork

In the long twilight that preceded the general availability of good navigational charts, our coastal waters teemed with small craft operated by fishermen. These remarkable seafarers would not have recognised an Admiralty Chart if you had given them one; many would have been unable to read the words on it in any case, yet most of them stayed out of difficulty for a lifetime. They did their navigation by the same rule-of-thumb pilotage tricks that we use today – and a whole lot more we’ll never know about. The chart was there all right, but it wasn’t made of paper and they carried all its data in their heads.

Although it did not matter to them, most of these fishermen only had a very small folio of mental charts. Two, or maybe three, was their lot. Take them a hundred miles from home, send them off to sea and they’d have been in deep trouble. Today, we are lucky. By using readily available charts we can relate what we see above the water to what lies beneath its surface anywhere on the planet. As a result, we are able to perform almost as well as the fisherman, not only on his home ground but anywhere we choose to operate.

Charts may form the basis of our navigation, but to use them fully, further information is required. Tides and other ephemeral data are found in almanacs. The bare essentials of the charted data are expanded and given vital colour by pilot books. Today’s almanacs are highly comprehensive and supply some basic pilotage information. While useful, however, this is no substitute for the real thing.

Paper Charts and Their Use

While many sailors navigate exclusively on electronic charts accessed via a PC or hardware plotter, many still prefer to use paper charts as their primary system, backed up by GPS and perhaps a small chart plotter. Even if electronic charts are the preferred first port of call, everyone must still have full paper backup for the gruesome day when the volts gurgle down some unexpected electronic plughole or the GPS system is switched off at source, for reasons we at the moment can only guess at. In other words, paper charts confer navigational independence. They remain the bedrock of our security and we all must retain a full understanding of what they offer.

Admiralty Charts

These are produced in all the different scales required to navigate successfully in British waters. They are available for most foreign waters as well but, in some cases, the locally produced charts are better for detailed navigation. If you were proposing to visit France, for example, you would be well advised to get hold of the French charts for the area you are intending to sail. Admiralty Charts, see Figure 1-1, will get you to most places and take you safely into the main harbours, but not even the UK Hydrographic Office can produce large-scale charts for all the inlets and anchorages of every coast upon Earth. Be aware of this if you are going beyond home waters and make suitable enquiries before you leave.

Standard Charts

The full-sized charts containing all the information available from the latest surveys are called Admiralty Standard Charts. These are sold by official chart agents and are up-to-date at the point of sale. The physical size of them can make for awkwardness on a small yacht’s chart table but, with practice, folding them is less of an issue than it may at first appear.

Leisure Editions

Leisure Edition Charts are sold already folded up in individual plastic wallets. They feature exactly the same information as the equivalent standard Admiralty Charts, but are printed on water-resistant paper said to withstand more rigorous use than the cartridge paper of the Standard Chart. Each Leisure Edition Chart is republished with a new edition to coincide with the Standard Chart on which it is based.

Figure 1-1 A UKHO Admiralty Chart of Northern France. In many ways these are the best charts for the yacht sailor, although they are not necessarily the best value for money.

Leisure Folios

The UK Hydrographic Office (UKHO) also produce charts suitable for small craft in Leisure Chart Folios. These are A2 size which works well for the average chart table. Each folio comes in a robust plastic wallet and typically contains 17 charts, all you need for its area of coverage.

These folios are undoubtedly very good value indeed, although a lack of overlap at the ‘joints’ can be a nuisance. It must also be said that a certain amount of fine detail is sometimes missed off which might be found on the equivalent Standard Chart. This discrepancy should be of interest to sailing schools and race navigators. It is less likely to bother a cruising sailor of modest navigational ambitions. Leisure Chart Folios carry a considerable amount of information on their reverse sides, which can include tides, radio services, symbols and abbreviations, as well as the IMO table of Life Saving Signals.

Commercial charts

In addition to charts published by the Admiralty, one or two commercial companies are also in the market place. Their charts are designed for yachtsmen from the outset, and sometimes include additional tidal, passage and pilotage information that can be very helpful. Imray charts are notable, adding value by including many plans, or blow-ups of harbours and other ‘hot-spots’ along the coast. Whether you use these or stick with the official publications is entirely a matter of taste, but an Imray chart of medium scale, complete with its inset plans, can offer a highly cost-effective compromise when it comes to backup for an electronic navigation system.

Figure 1-2 Part of an Imray chart, designed for small-boat navigation. Compare with the Admiralty Chart shown in Figure 1-1 and note the differences in presentation – colours, visual representation of light sectors, and so on. Note also the added value in the useful plans, of which a number are to be found on this and most Imray charts. Like Admiralty Leisure Editions, these charts are folded like road maps.

Admiralty Chart Number 5011

It is assumed that readers have some basic grounding in chart work, so no space is wasted on describing what the various symbols mean. Nobody, however, can carry the full list of chart symbols in their head. For that reason, every yacht should be equipped with a copy of Admiralty Chart Number 5011. This excellent publication which, incidentally, isn’t a chart at all, rather more of a booklet, lists the whole lot. Buy a copy and keep it in that small room which most sailors visit once a day. Necessity can then be turned into the virtue of time well spent studying its colourful pages.

The Admiralty Chart Atlas

This useful publication is available for study at all chart agents, or you can buy one for yourself. If you intend to sail in many different areas, the investment is well worthwhile.

The information is presented as a single-line map of the coast. The charts covering it are marked and indexed clearly so that by glancing at the atlas you can see immediately which ones you are going to need.

Paper chart requirements for a passage

Admiralty Charts are available in various scales. They range from overviews showing the complete North and South Atlantic Oceans on one sheet, down to harbour plans depicting every pile driven into the seabed. With a selection like this to choose from you should be able to find what you want, but with boating costs being what they are, the question often asked is, ‘What charts do I actually need?’

Since charts are far from cheap, nobody wants to buy more than is necessary, but there are few feelings worse than plunging up a narrowing channel with the tide behind you wishing you had bought that last harbour chart instead of last night’s bottle of port. In order to make a coastal voyage, the first chart is an overall passage chart. This should have on it both the departure point and destination. It is upon this that you will draw up approximate courses to steer, and work out a passage plan.

If the voyage is going to be a long one, the detail on the passage chart may well prove insufficient to allow you to plot progress satisfactorily. If so, a series of coastal charts on which to work as you go will be needed. For the arrival, a harbour chart to guide the yacht through the intricacies of the entrance and up to her berth may well make all the difference. If the passage looks like passing close to the shore at some point, make sure there is a chart available to give as much detail of that area as may be needed, see Figure 1-3.

Figure 1-3 Sections of three charts for a voyage along the South coast of England from The Needles to Poole harbour: an overall passage chart (Scale 1:150,000), a zoom-in of a coastal chart for the run-in to Poole entrance (Scale 1:75,000), and a tight crop of the harbour chart for Poole showing all the details at the harbour mouth (1:12,500).

Paper chart plotting tools

■ Pencils

In order to be able to plot courses, bearings and distances successfully on the chart, you’ll need a few simple tools. The first is a soft, well-sharpened pencil (2B grade is about right). Soft pencils make a solid black line and, because you don’t have to press down hard on them, they don’t score the surface of the paper. This means there are no marks left on the chart after a line is rubbed out. It is a false economy to use any old pencil; treat yourself to a box of decent ones, and keep a small, sharp knife in a special place. Its sole job is to hone up the chart table pencils, so clap in irons the man who uses either your sharpening knife or pencils for anything other than their true purpose.

■ Eraser

The second implement is a clean, gentle eraser. Charts are beautiful things. Don’t mess them up with a dirty old eraser palmed from your youngest child’s pencil case. Keep the ship’s in a safe place.

■ Dividers

When it comes to measuring distance, dividers should be as large as convenient and, preferably, of the ‘one-handed’ bow type. It takes very little practice to be able to use them with one hand, leaving the other free to grope for the plotter, your hip-flask, or just simply to hang on. Distances, of course, are always measured from the latitude scale at the side of the chart and not the longitude scale at the top.

■ Parallel rulers

These are the traditional way of transferring a line from anywhere on the chart to the nearest available compass rose. Unfortunately, in a small yacht, they give rise to a number of difficulties. For example, just as you are making the final ‘step’ with the rulers, one leg will run into the fiddle on the edge of the table or fall foul of the cable dangling from the radio mike, and you’ll have to start again. Infuriating on the third successive occasion.

Parallel rulers aren’t much good on commercial charts either, because every time you step across one of the many fold lines in the chart, the rules will slip. You don’t need this additional aggravation when feeling seasick. They also require the use of both hands, but when a yacht is heeled at thirty degrees and bouncing from wave-top to wave-top, it takes at least one fist to keep you in the seat. All in all, parallel rulers are about as much use in a small sailing yacht as an umbrella.

Fortunately these problems are all easily solved by using one of the many plotters on the market. By far the best and most common are those designed along the lines of the ‘Breton Plotter’.

■ The Breton Plotter

The Breton Plotter first appeared in the 1970s. It rapidly established itself as the instrument of choice for the thinking small-craft navigator and now has many imitators, most of which do the job equally well. Because the electronic chart plotter is now established, we have two completely different items with the same general name, so for the purposes of this book I shall refer to the chart plotter (as in ‘plastic device for measuring angles and lines on a paper chart’) as a ‘chart protractor’.

These chart protractors incorporate a 360° circle which can be swivelled to any angle. The main body of the tool has a black line running down its long axis and through the middle of the circle which can be thought of as a compass rose. To use the instrument, the compass rose is orientated with the north-south, east-west grid lines you’ll find on any chart, and the main body is swung ‘underneath’ it to line up with the course or bearing being measured. The black line on the protractor body now cuts the rose at the angle you’re looking for, see Figure 1-4.

Breton plotters usually carry a variation scale which can be marked up for the present location, thus enabling you to read off the course as either magnetic or true. Being old-fashioned and British, I’m a lot more comfortable working in true, but I know my colleagues in the United States prefer to think in magnetic all the time. Whilst recommending you to follow my example (and that of the Royal and Merchant Navies), I can live with the other method, so long as one remembers that all transits and bearings on the chart are given in degrees ‘true from seaward’.

Figure 1-4 To determine a course or bearing, a Breton Plotter is laid along the line you’ve plotted (A) and the grid on the central rose is aligned with that of the chart (B). The bearing is read off against the mark indicated (C). Note that you can use magnetic or true, once you’ve entered the variation onto the plotter scale.

Electronic Charts

Electronic charts are now in common use, either in stand-alone ‘hardware plotters’ of the type you see on the bulkhead of many yachts, or as the display part of a piece of software embedded in a PC. These charts come in two formats.

The Raster chart

A Raster chart can be thought of as a scan of an equivalent paper chart, see Figure 1-5. It works within the same boundaries and has the same serial number. Most Raster charts are based on those issued by the national authority. This is the UKHO in Britain, and the charts featured are Admiralty Charts. The private cartography company Imray also issues its charts as Raster scans.

For the conservatively minded, Raster charts have the benefit of looking just the same as charts have always done, and all their data are visible while they are up on the screen. This means that unlike their Vector equivalents, the operator doesn’t have to work at a series of buttons to reveal everything they have to tell him. As you zoom in and out on a given chart, nothing changes except the size of the image. There are no surprises.

Figure 1-5 A Raster chart from the Admiralty Raster Chart Service (ARCS).

One drawback of Raster charts is that unless the ‘kit’ is blended together electronically (sometimes called ‘quilting’), you have to decide personally which chart to use and switch from one to another. I don’t mind this a bit myself, but some do. The other downside is that they generally need a PC plotter to run them. This can be a laptop which most people now have, so it’s only a problem for a few.

Vector Charts

These are built up by a different process from the raster scanning with the result that what you see doesn’t look at all like paper charts created from the same set of data. At extreme zoom out, you’ll find no detail of any sort beyond some basic outlines, as in Figure 1-6. Zoom in and interrogate the chart with the buttons supplied, however, and every scrap of available information can be accessed at will, so long as you’ve found out how to do it, see Figure 1-7.

Figure 1-6 A Vector chart zoomed out.

Figure 1-7 The same Vector chart zoomed in to a workable scale equivalent to the Raster chart in Figure 1-5.

The zooming process is seamless and the borders of the various charts that went into creating the flash card or chip will be invisible unless you choose to display them. Thus, the whole of the British Isles, for example, can appear as one single chart.

Vector charts issued on flash cards or some similar medium are the charts of choice for hardware plotters, but they can also be found on CD-ROM for use on PC-based plotter programs. Their great drawback is that, unless you zoom well in, you might want more details than you’re getting, but if you go in tight enough to see all you need, you’ve kissed the vital overview goodbye.

Chart Corrections

Whether you buy them or borrow them, it is your responsibility to see that your charts are up to date. A new Standard Chart from a recognised chart agent will be corrected up to the day of purchase. This is part of the service. Others may not be so up to date, although Imray’s charts come with a correction slip as new as they can possibly make it.

Notices to Mariners

Every week the Admiralty publishes Notices to Mariners (NMs) online. All Admiralty Charts which require correction are listed with details of the necessary corrections. However, while these might be of great value to a world cruising yacht fully equipped with charts and able to get hold of the Notices regularly (a very rare bird indeed), most of the information they contain is of no interest to the home waters yacht navigator. Being aware of this, and because of the growing numbers of small vessels, the Admiralty now issues a Leisure Edition of the Notices at www.admiraltyleisure.co.uk/NMshome.asp. The Small Craft Notices do not generally concern themselves with depths greater than seven metres or with other items not considered to be of interest to the operators of small craft, but they are free, highly accessible, and a great service to use.

Recording corrections

Each NM carries a serial number. When it is applied to a chart, the convention is that it will be noted in the bottom left-hand corner so that any user can see how current the chart is. A chart that has been corrected by the printer carries the same data, see Figure 1-8. Note also the date of issue.

Figure 1-8 Part of a Standard Chart showing any corrections. The chart should be up to date when you buy it, but keeping it up to date is your responsibility.

New editions

Every so often, when the number of corrections on a chart gets out of hand, the Admiralty will issue a new edition to supersede the old one. The Notices to Mariners will advise when this is about to happen.

Navigation Warnings

These are issued daily by Coast Radio Stations, so if you are monitoring your VHF channels or have a Navtex machine they will keep you right up to date with what is going on in your sea area. Buoys off-station, lights temporarily out of order, dredgers dredging, cable ships to be given a wide berth and so on are all mentioned. The Notices to Mariners can be accessed via the Internet, but Navigation Warnings are instant, so keep abreast of the latest developments by listening at least once a day.

Projections

Because the survey data that make up a chart are printed on representational pieces of paper rather than etched on sections of a globe that is the spherical reality, some distortion of scale is inevitable. The bigger the area covered by the chart, the greater this will be. Only if a chart depicts a vicinity small enough to be considered flat is there no distortion at all.

The Mercator projection

The Mercator projection is the workhorse of the navigation table. The vast majority of charts used today are built on it. With a Mercator projection, all the meridians of longitude are parallel, see Figure 1-9