Features October 1, 2003 Issue

Offshore Log: Back to School

We harp on the theme of learning and maintaining piloting skills. People tire of it, but it must be done. Here's another example.

By Nick Nicholson


You're tearing along at seven knots, trying desperately to reach harbor before total darkness. Suddenly you're aware that visibility is deteriorating—your running lights are reflecting back at you, and it seems darker than it should be for this time of day. It's not just getting dark—it's getting foggy. Visibility must be a lot worse than you thought, and your palms feel cold and wet, much more so than justified by the weather.

Don’t let your electronic love affair diminish your real affection for charts, log-keeping, and piloting. There lies the way.

You're not worried, though. The autopilot is driving the boat, leaving you plenty of time to look around. Waypoints in the GPS are controlling the autopilot.

Suddenly an electronic alarm pierces the quiet of the cockpit—the autopilot is not happy. Glancing at the computer screen, you see a red box on the menu, glowing its frightening message: "No GPS." Another alarm sounds. It's the GPS itself this time, confirming your worst fears: "No GPS position," it taunts.

What's going on? Are you panicked, or relatively calm? When was the last time you wrote down a position? Do you even know what direction the autopilot was steering? Do you know where you are?

Can't happen to you? Hate to disappoint you, but it happens all the time. Here's a recent real-life example.

On July 8, Temptress was closing in on the finish line of the Marblehead-Halifax Race. Visibility had been limited for much of the last 24 hours, and was now approaching zero. We weren't really sure how bad it was until a fishing boat appeared out of the fog, no more than a few boatlengths away. His low-slung wooden hull had not shown up on our radar, even though I had the range set to three miles, frequently toggling up to six-mile range and down to 1.5-mile range to try to pick up anything that might either be farther away or so close it couldn't be seen on the three-mile scale.

As often happens, the target lit up when the radar finally painted it a quarter mile away—after our close encounter. This is not an unusual scenario. Small boats—particularly low-profile wooden or fiberglass boats, and more particularly if there is any sea running—make lousy radar targets. They may disappear in the trough of a wave just as your radar is scanning that sector, or they simply may not reflect your radar's signal well.

Just a week after this race, in the same area and identical conditions, a big southbound Swan collided with a northbound Hinckley, resulting in serious damage. Both boats were keeping radar watch, and neither had seen the other. Miraculously, no one was injured. Both boats made port safely.

From Bad...
In our own case, darkness was falling, and with it any remaining shred of visibility vanished. I stayed below, glued to the radar, the computer screen with the charting and instrument panel programs running, and the GPS. Every 15 minutes I updated the position in the hand-written log, and every hour I plotted the position on the paper chart as a backup to the charting software. As we got within four hours of the finish—moving onto a larger scale paper chart—my manual plotting interval was reduced, first to a half hour, then to 15 minutes when we were within two hours of the finish.

The waypoints entered in the GPS and charting program were also plotted on the paper chart. As a precaution, I had not only taken the mark positions provided in the sailing instructions, but had lifted the positions directly from both the electronic charts (Canadian government raster charts) and the paper charts.

What I had discovered was far from reassuring. Positions derived using the three methods differed from each other by as much as several hundred yards. Which one was right, and how much difference did it really make? Unfortunately, it could make a lot of difference. Several of these marks were keep-offs that marked dangerous shoals, not to mention the fact that they were marks of the course that had to be observed. With zero visibility—and a racing boat moving at eight knots—there would be little time for making corrections.

Fortunately, all these waypoints coincided with aids to navigation. Would it be possible, then, to make corrections using the radar? Yes, but there's a big caveat here. If the radar is not perfectly aligned with the fore and aft axis of the boat, it will give you a false impression of the position of the target. In addition, if the radar is linked to an electronic compass, any errors in that compass will creep in if you're using a compass bearing rather than a relative bearing on the radar screen, especially when you're calling out steering corrections to the helm.

In our case, I knew that the radar was not properly aligned. The boat was new, and a quick check on some targets during a delivery showed a significant radar offset, but one that we had not had a chance to eliminate. The normal correction routine would be to point the boat directly at a visual target that would also be a good radar target, then check the relative bearing of the radar target. Virtually every radar has an internal alignment program to correct installation errors, but the function is often buried deep in the installer's setup routine to prevent accidental changes by the operator.

Even the best professional installations may well be misaligned, as the final corrections can only be done underway. In our case, my rough eyeball correction was 10°. Later, doing the correction routine properly, we discovered that the actual error was closer to 14°.

...To Worse
So here we are: zero visibility, inconsistent plotted positions of important marks, and a radar with an uncorrected alignment. Oh yes, there was also a race to win, so simply stopping to sort things out was not an option—at least not an option that would stop the crew from lynching me. Could anything be worse?

Sure. About this time, the "No Position" GPS alarm went off. The GPS re-acquired, then lost position again.

I went instantly to the log (on the table in front of me), pulled the last position, plotted it on the paper chart, then ran the dead reckoning forward by the boatspeed, elapsed time, and course steered. Within a minute or so I had a new estimated position. Here was a good example of why we keep logbooks, and keep time, and have calculators on board.

By the time I had done the manual plotting, the GPS was happy once again, and we were tracking, still without any visual reference whatsoever, towards the finish. But with renewed realization of the fragility of electronic navigation, I continued the constant manual plotting all the way to the finish.

Halifax has a traffic separation zone, complete with a vessel control system. We had already checked in with Halifax Traffic, which had listed commercial traffic which might affect us. After more than two days of racing, we knew that the only racing boat anywhere near us was about two miles ahead, and therefore not a problem. The course should be clear of mobile obstacles.

But which of our waypoint positions would prove correct? Lacking a visual reference, there was no way to know until the marks popped up on the radar, and even then the reference had to be taken as relative rather than absolute.

Hedging my bets by deliberately aiming slightly to one side of the waypoint—knowing full well that the crew would kill me if they knew we had sailed even a few extra yards—I made sure that we would pass on the safe hand of the marks, but we had to be close enough for positive identification in the fog. When the first mark popped up on the radar at a range of about a half mile, I tweaked the course a couple of degrees to close the mark. When we finally saw its glow, very briefly, we estimated visibility at about 25 yards. The tactician in the rear of the boat twigged to what I had done, and chewed me out for sailing extra distance. I was too busy to argue much, but did suggest he perform a physically improbable and morally questionable act on himself.

The finish itself was much the same: zero visibility, a mark on the radar that did not coincide exactly with any of the charted positions. It was not a casual conclusion to a relaxing race.

As wonderful as they are, today's electronics are increasingly complex and interdependent. Inexpensive radar, chartplotters, and GPS receivers have led to an alarming decrease in piloting skills, at the same time they have taken much of the anxiety out of navigation.

I am no Luddite, bent on wrecking labor-saving machinery to save my job as a navigator. Nobody loves electronics more than I do. But the fact remains: The prudent navigator never relies on a single method to determine position. Navigation is the art and science of safely conducting a boat from one point to another. You may think your most important navigation tools are electronic, but they may really be a paper chart, a straight-edge, and a pencil.

Comments (2)

Totally rely on GPS offshore? Hell, it makes me nervous to be in a car without a paper map but my girlfriend seems to get lost with her GPS on a regular basis.

I ALWAYS have current charts with me on my sailboat - a Bavaria-44 (6.5' draft)- the following story would not have been possible with my sailboat.

The most intense GPS situation I've ever had was idling (literally) at about 2 knots southbound down the ICW in the fog in my PDQ-34 power cat (~2.5' draft). I was on the far right hand side of the channel and passed passed several bosts going northbound with at least 50' between us. I never felt unsafe, or even uncomfortable, but you can bet your ass that I was paying close attention to the charts and my position.

I was navigating using "Offshore Navigator Lite" on my Dell notebook computer. This program has significantly more detail than my on-board GPS and presents everything in many more colors.

But, I crosschecked our position at every channel marker and we were never more than about 10' off. I believe that we were so close because of the very high rate of GPS position update relative to boat speed.

Posted by: Max Pucker | May 23, 2011 9:39 AM    Report this comment

Racing into danger, for a few yards...

Posted by: San Juan Sailor | May 22, 2011 8:55 AM    Report this comment

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