Circles of Uncertainty

Electronics — April 2005
By Ben Ellison

Circles of Uncertainty
An encounter with electronic chart skeptic Nigel Calder.

 More of this Feature

• Part 1: Circles of Uncertainty
• Part 2: Circles of Uncertainty
• Electronics Q&A
• Simrad Navstation
• Lightning Guard 200
• RAM Mount
• Airmar

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Yeeeee-ha! As I write this I’ll soon be jetting from the dark of a Maine winter toward a Miami boat show aglow with bright new electronics. I’m particularly psyched to get a first look at two major new chart-card formats called C-Map MAX and Navionics Platinum. One or the other, or both, can purportedly put photomaps, nav aids that blink realistically, 3-D land and/or bottom contours, coastal roads, and much more onto a new generation of supercharged plotters. Look for complete coverage in our June electronics issue, but from what I understand thus far, enjoying the sublime freedom of the sea—the ability to nose around anywhere there’s enough water to float our boats—is about to get even easier. Meanwhile, wouldn’t you know it, I’ve just been persuasively reminded about some niggling electronic chart issues.

The agent of persuasion was a chap named Nigel Calder. First, a quiet blizzard-bound boat show allowed me to really pay attention as Calder delivered a cautionary seminar based on his fine book How to Read a Nautical Chart. Then a cancelled mutual flight led to our sharing a rental car for a somewhat desperate eight-hour night passage back to Maine, giving us plenty of time to argue about his digital chart reservations and share some sea stories, too. Allow me two observations about Calder before we get to the issues: One, he is possessed of a sharply inquisitive and methodical intellect; two, he’s also a “full-speed ahead, damn the torpedoes” kind of guy who’s gone aground more times than any other skipper I know!

Calder, already the author of several respected books about boat systems (see “Q&A,” this story), originally figured he could knock off How to Read a Nautical Chart (International Marine, 2003) in six weeks. The goal was an expanded version of what NOAA used to publish as Chart #1, a sort of detailed dictionary of all the symbols and nomenclature used on U.S. and international charts. Part two of Calder’s work is exactly that, Chart #1 greatly enhanced with added illustrations and real-world explanations, and it’s invaluable whether you’re using traditional paper charts or their digital translations. It’s what’s lost in that translation that sidetracked Calder, leading to months of research, visits to various hydrographic offices, and part one of his book.

If I had to boil down Calder’s analysis of what’s gone missing during our high-speed voyage from traditional navigation to GPS plotting, the phrase might be “a sense of uncertainty.” In the old days a navigator’s relatively poor tools and resulting caution usually more than made up for typical chart inaccuracies. Now, notes Calder, “Our tools are much more precise than our charts.” The navigation proposition has inverted! Not only do we have WASS GPS plotting our vessel every second to around ten-foot accuracy (most of the time), but the actual data on our spanking new chart may be quite antique. I understood this general situation but was still fairly shocked to discover—prodded by Calder—that extensive areas of my local charts are sourced from a “pre-1900 survey, partial bottom coverage.” That means guys getting soundings with lead lines and positions by triangulating shore features!

Old data may explain certain anomalies I’ve…err…run into out there, and it certainly explains the January tragedy in which a U.S. nuclear attack sub—cruising at 33 knots, 500 feet deep in waters near Guam that were charted at 6,000 feet—slammed into an undersea mountain now estimated to be almost a mile wide and topping out at 100 feet deep. It was later reported that the peak appeared in 1999 satellite photographs, but no agency had had the resources to use them for chart updating. Lest you think this is only a submarine problem, check out Calder’s illustration showing a 1835 sounding of an 18-foot deep coral head that’s still on the charts but has grown, as coral does, darn close to the surface (something he knows…bump…for sure). In the book he also reproduces a “sobering” IHO graphic indicating that at least half the surveys used in many parts of the world, including ours, are less than adequate by current standards. Those standards are high but dreamy, as Calder believes that the actual resources going into new surveying are at a several century low, largely because they’re being eaten up by the switch to digital cartography.

Next page > Part 2: So-called “overzooming” on our plotter or PC may make the details easier for us to see, but doesn’t improve the accuracy a bit. > Page 1, 2, 3, 4, 5, 6, 7

This article originally appeared in the April 2005 issue of Power & Motoryacht magazine.

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