How to Read a Nautical Chart

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How To Read A Nautical Chart by Nigel Calder is not a normal book.Most of us sailors think that we can read a nautical chart. Nigel states in his introduction that after thirty years of reading and collecting nautical charts, he thought he pretty much knew how to read a chart. After doing the research for this book, he learned a whole lot more about reading charts. And this is from a man who has created charts of Belize and Cuba for his cruising guides.He starts by delving lightly into the history of charts, and then covers how charts were made before aerial and later satellite photography. He point outs out that old-time surveyors could, if they took their time and cared about accuracy, could produce amazingly accurate charts and maps. A survey made of the US in 1927 is never inaccurate by no more than 160 feet from Kansas to the East coast!He then points out that while new charts are often ‘corrected’ by aerial or satellite photography, the survey work (i.e. depth soundings) are often ancient. For example, the ‘newest’ soundings of Honduras were made in 1835, 26 years before the War Between the States! In fact, the only soundings ever taken in most of the Indian Ocean were made by Captain James Cook in the 1700’s. Even today, more than 50% of the soundings on charts issued by NOAA and the British Admiralty (the two main providers of nautical charts) are taken from sounding poles or lead lines, not sonar. This means that projections can be sticking up that are not found until someone hits them. This happened to the liner Queen Elizabeth 2 in 1992, when she hit an unmarked seafloor projection off the US coast. He also points out that things change over time. For example, most coral reefs grow about 16 feet vertically every 100 years, meaning that with many soundings over 100 years old, depths in tropical regions are often very inaccurate today!Another interesting item Nigel brings up is that some hydrographic agencies (British Admirality, Canadian, and Cuban, for example) require that companies that sell their charts bring them up to date before sale, while others, like NOAA, have no such requirements.Nigel then provides an interesting discussion of the limits of accuracy, both vertical and horizontal, and even a full page discourse on why your GPS says you are 24 feet below the earth when you are sailing along the surface. Lastly in this section, he talk about the different projections used in making charts, Mercator and Gonomic, and when to use which. He also talks about the differences between NOAA charts, NIMA charts (US charts of foreign areas), British Admirality charts, and the privately made charts of Stanfords and those made by Imray, Laurie, Norie and Wilson. Lastly, and most importantly, he describes why Latitude and Longitude readings from your GPS sometimes differ from those shown on charts.In the next section, Nigel introduces us to some of the symbology used in charts. He especially points out that no country or company (except the French) completely follows all the standards devised by the IHO (International Hydrography Organization). However, as the IHO standards allow for ‘national requirements, reflecting a country’s needs or preferences, to introduce minor variations into the specifications’, this is acceptable. For example, NOAA charts are still largely produced in imperial (feet and/or fathoms) units rather than metric. Also, many charts use a different color coding system to identify shallow or deep water, rather than the IHO standard.Now, Nigel comes to the meat of the book. The IHO specifies that all chart symbols are divided into sections, labeled A through T. Section A is called the General section, and this covers the non-cartographic information on the chart, such as title, numbering scheme, margin notes, and notes on the charts. Section C deals with nautical features, Section I with depths, section Q with bouys and beacons, etc. Nigel discusses each section in detail, with examples from real charts plus the symbology used on all the major ‘brands’ of charts.All in all, I found reading How To Read A Nautical Chart a very interesting and valuable experience. I would rate it 4.75 stars (out of 5), the only thing lacking was a way to better correlate his text to the associated maps, and a side-by-side comparison of a NOAA, British Admiralty, and possibly a private chart of the exact same area.

A good lesson in this book that might possibly have saved the Costa Concordia.With the extreme accuracy of modern GPS systems it is sometimes tempting to go close to various types of marine hazards. However the charts , even those used for navigation systems, are not always so recently surveyed and their accuracy might not match those of your boats systems.It so well presented interesting book packed with useful information and items of general interst

Since the current U.S. Administration saw fit to cease publication of CHART NO. 1, the government's own guide to reading maritime maps, back in 2000 (maybe they figured Dubai might pick up the slack around our harbors), HOW TO READ A NAUTICAL CHART is an absolutely crucial educational volume for those of us new to reading charts.It's all here. Nigel Calder does a splendid job of taking the esoterica of chart symbolism and language and turning it into something any boater can understand in everyday terms. He also does a fine job delineating the differences between harbor charts, large area charts, GPS readings and so on, all of which have their own internal but non-complimentary logic.If you leave the dock, knowledge of and familiarity with charts can avoid costly errors, save your boat, and literally save your life. HOW TO READ A NAUTICAL CHART is a reference you must have.

This book has really helped me with my RYA studies and has also helped to explain some of the mystery of nautical charts. I would seriously recommend this book for anyone studying the RYA excams at any level. The book is clear & concise in its explanations.