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One
of the most unforgettable moments—highlights would be the wrong
word—at the annual NMEA conference last fall was a boating accident.
A bunch of us were enjoying an alfresco breakfast at the Sanibel Harbor
Inn and Resort in Fort Meyers, Florida, when the balmy peace was disturbed
by a loud crash coming from the little marina. It was closely followed
by shouts and then sobs. A few of us investigated. I even took a picture
of the incident (above) and for the first time felt like a predatory journalist,
because what we saw was a traumatized skipper and his family in a scene
of the yachting dream gone suddenly sour.
All
this man had tried to do was back off a pier onto a flat-calm Sanibel
Sound. What he had not figured in was the roughly 1 1/2-knot current quietly
pushing him onto the dock, and—much worse—onto the sharp bow
of a big steel tour boat tied up beyond. Then he’d compounded his
mistake by trying to power out of it. It must have been an excruciating
moment when that steel bow blew through the big starboard window and into
the main cabin where his teenage children were gathered, and then ripped
the cabin corner post out of his vintage sportfisherman.
Now
let me emphasize that I have no desire to embarrass this man. In fact,
I regret to report that, judging from his family’s response to the
accident, his dream boat is probably finished. Sure, he should have been
aware of the current, but I bring the whole subject up because I fear
that he’s just one of too many new boaters who’ve failed to
develop a solid sense of the fluid dynamics that can so affect close-quarters
boat handling, not to mention offshore navigation. And a prime culprit
is our wonderful electronics! I’ve observed even experienced skippers
having trouble understanding where current fits into all the readouts
on their bridge.
So
let’s step back a moment to the days before Loran or GPS could constantly
plot our true position. Back then, anyone who ventured beyond the horizon
or into a fog bank soon developed a gut-level understanding that the water
they were moving through might very possibly be simultaneously moving
them somewhere else. They sought guidance from current tables, even though
such data is pretty spotty, particularly along coasts complicated by islands
and capes. And, since current activity is invisible without a fixed reference,
they were always eyeballing the subtle wakes around navigation buoys and
the like (lobster pots, pesky as they are, work nicely for this).
Such
pencil-and-chart navigators learned to think in terms of the vector math
that is considered grade school stuff today. Vectors are simply graphic
expressions of direction and speed that can be added together to figure
out the true motion of something that is traveling in two directions at
once. At the heart of traditional navigation is a holy triangle of such
vectors. One describes a boat’s heading, or course, and speed through
the water and is the essence of dead reckoning, or DR. Another defines
the direction and velocity of the water itself, known as set and drift
and usually caused by tidal forces. And the third, their sum, shows what
the boat is actually doing; i.e., course and speed over ground (COG and
SOG).
The
illustration on page 46 shows how an old-school navigator might guesstimate
a current vector to correct his DR and figure out where the heck he really
is. There are more elaborate techniques for adjusting course to compensate
for set and drift, but they hardly matter these days. A GPS can deliver
accurate (at least on average) COG and SOG every second and, better yet,
can constantly plot your real track over the ground on a digital chart
while displaying spot-on bearing and distance to a desired waypoint. Keep
your boat in the middle of that nice highway display, and you don’t
really need to know beans about current.
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