As we approach the holiday season, I’d like to suggest two reference titles that might make perfect presents for the professional mariner in your life.

The first is the second edition of “How to Read a Nautical Chart” by Nigel Calder. The subtitle, “A Complete Guide to Understanding and Using Electronic and Paper Charts,” defines the broad scope of the subject. I can just hear the groans and see the rolling of eyes from fellow mariners in the towing industry. I’ll bet the initial reaction was, “I’ve been doing this for a long time and I know how to read a chart!” But do you? Or, more to the point, how well do you know how to read a chart? The question doesn’t have a simple answer. 

There are many shades of gray here and I think that any professional mariner probably has room to improve in this fundamental and extremely important subject. It’s dangerous and foolish to assume that you already know all you’ll ever need to know about charting. 

Furthermore, our reliance on GPS and the various electronic charting programs has its drawbacks. To quote Calder, “In this age of satellite positioning systems and pinpoint navigation, the tools with which we navigate are significantly more accurate than those used to conduct most of the surveys on which our charts are based. Our tools may also be more accurate than the tools and techniques used to draw those charts (paper or electronic).” 

Another book for the professional mariners on your holiday gift list is “Beyond the Moon: A Conversational Common Sense Guide to Understanding the Tides” by James Greig McCully. Why would anyone but a rank amateur need to read a book like this? As McCully writes, “The world is full of people who use the tide tables every day but do not understand the forces of nature that generate the tides.” The book was published in 2006, and when I read it, I wished it had been published sooner. It hits the sweet spot between too much techno-jargon that can’t be followed by a non-scientist and the overly simplistic explanations that are offered virtually everywhere else. 

Because of its sometimes mind-blowing complexity level, I doubt that it’s possible to completely understand the phenomenon that is the tides. But that shouldn’t prevent us from trying to do better, nor should it prevent us from dispelling some of the common confusion between tides and tidal currents. The short version is that tides are the apparent vertical movements of the sea level, in response to the gravitational pull of the moon and to a lesser extent the sun, and the movement of the earth. It should be expressed as rising, falling or standing. Tidal currents are the horizontal movements of the water induced by the tides, and should be expressed as flooding, ebbing or slack, and occasionally as rotary. So there’s really no such thing as a “flood tide” or an “ebb tide.” It’s a misuse of the terms that mariners commonly indulge in. 

Of course, this is a vast over-simplification, but the book delves into it deeply enough to satisfy nearly anyone’s curiosity. In addition to the aforementioned forces, there are nearly 400 other factors that affect the tides to one degree or another. But most of them aren’t significant except in the aggregate, and McCully does an admirable job of distilling all of this complexity down into something that’s understandable and usable for the average mariner.