The other day I was driving along I-95 just west of New Haven (on a stretch once described to me by a long-haul trucker as "the worst piece of road on the continent, including Baja.") in moderately thick traffic that was moving along at about 60 miles an hour. I was in the right lane, with a lot of space between me and the car in front.
A huge SUV (I don't know what it was - a Ford Tyrant, Oilman's Edition? A GMC Compensator?) came charging down an open space behind me at about 80, swerved into the left-hand lane, hit the brakes, and then camped on the rear bumper of the last car in line there. In the course of the next several minutes, this SUV changed lanes several times, was never more than about four feet away from the car in front of it, and by dint of some breathtakingly risky maneuvers, got about a quarter-mile ahead of me before taking its exit. I took the same exit - about 15 seconds later.
I'm sure I ended up just as stressed as whoever was in the SUV, because I have a severe adverse reaction to people who have no clue about the relationship of speed, time, and distance.
Sailors know the equations: Time x Speed = Distance. Distance / Time = Speed. Distance / Speed = Time. Convert to and from decimals as needed.In a watery world with no roadsigns and few distinguishing marks, these equations - or at least the import of them - become deeply ingrained, such that one eventually becomes aware of the relationships in all situations, no matter what vehicle or medium one is traveling in. Good racing sailors have a well-tuned sense of these things - they can judge the distance to a starting line or the time to a layline with remarkable accuracy. Practiced long-distance navigators are similarly accurate, whether they're Polynesians using the movement of stars and the cadence of wave sets, or Joshua Slocum using a wind-up clock, or Horatio Nelson using a timer and logline.
The original Dutchman's log was just that - a piece of wood that the navigator tossed off the bow. He walked aft, counting the seconds until it reached the stern, then divided distance by time to learn the speed of the vessel. For example, say a 60-foot vessel takes 5 seconds to sail past the log. That's 12 feet per second, 720 feet per minute, 43,200 feet per hour, divided by 6,076 (the number of feet in a nautical mile) - or 7.1 knots. (Of course a smart navigator on that 60-footer would develop a simple reference table.)
In 1637, Engish navigator Richard Norwood figured out a system composed of a line knotted every 47.25 feet and a 28-second sand timer: If the first knot in the line passed through the mate's hand just as the sand ran out, the ship was going 6,076 feet per hour, or one knot. After that, presumably, the oceans became less littered with wood chips.
We spend a fair amount of space in this publication discussing the need to keep manual navigation skills tuned up, even as we welcome cool developments in electro-navigation. It's not just about safety, simplicity, expense, electrical demands, water-resistance, and all that. Some ingrained practices lead to better awareness of surroundings, of what's possible and impossible, practical and impractical, maybe even wise and unwise. If we can just stay familiar with the relationship of speed, time, and distance, maybe we won't end up like the driver of that SUV - stupider than a moth flinging itself against a lightbulb.
In the October 15 issue we're going to look at some marine wristwatches - a sampling of the big selection out there. In the meantime, here are a couple of Web addresses that will help you tune up your timepiece: http://nist.time.gov (from the Time and Frequency Division of the National Institute of Standards and Technology) and http://tycho.usno.navy.mil (from the U.S. Naval Observatory Master Clock.)