Dead Reckoning

Fog – my Dad used to take off pell-mell into the thick of it, armed with only a chart, parallel rules and sharp ears. Pre-electronics, the process was to lay a course from where you were to some mark, and then ‘walk’ the parallel rules across the chart to the compass rose to get the magnetic course. The chart course would be accurate (if you were strict with the parallel rules and checked your work), but was your own compass as accurate? given that large bits of metal like the engine could throw it off.

(There were compass adjusters in those days who would carefully take your boat in all directions, comparing your compass to their shielded one. They would then fasten magnets in odd places on your boat to compensate – it was an art to get it within a couple of degrees of accuracy the compass ‘round.)

In this process of ‘dead reckoning’, the course and the compass were as accurate as it got. From here on in you made your best guesses for leeway – you lose a few degrees downwind depending on its strength – and for tide, which you measure by watching the lobster pots along your way if there are any and recalculating if you enter a contrary tidal stream.

Preferably you’re going for a ‘noise-maker – a bell, a gong, or a whistle – which widens the target circle to the diameter of the sound. The calmer it was, the smaller the radius, and the circle was offset downwind of the buoy – harder to hear them upwind. Even in the calmest seas, the clappers would hit the metal bells somewhat, but on a calm day the whistles wouldn’t even groan; they’d just sigh, and you had to be right on top of them to find them.

If you were going for a simple can or nun, the target circle was determined by the visibility, often just a few hundred feet. In a 3-mile run, it’s easy to have a few hundred yards of error. You estimated your speed, so when your 3-mile run was done and there was no buoy, your start tacking back and forth in search of it. Often enough, it simply wasn’t findable, and you would set off for the next buoy from your guestimated position.

If you were heading for a point of land or an island, whoever was on bow watch was all eyes and ears for the thunge of wave on rock or the sudden appearance of a line of surf. Having been there many times, I can tell you the fog is deceptive, and you find yourself searching the water just in front of the boat, or the sky as you gradually lose your sense of horizon, since there is none. If the surf appears unexpectedly, it is a cause for much yelling and an immediate turn of 180 degrees – at the least you know the water you came in on was deep enough.

If you were sailing, you could hear the fishing boats around you, but other sailing boats – other fools out in the pea soup – were silent, so you blew your tin foghorn every two minutes to warn others of your progress. I still have his old foghorn right in my cockpit, and although the new shrill freon horn penetrates the fog better, I still use Edward’s old horn in anything less than an emergency situation.

And I think of him as my own navigational skills fade to nothing. (He didn’t brave the fog alone much; it was at least a two-person job – can I say that in my own defense?) As Annie and I sail in a 100’ circle of grey for 15 miles from Vinalhaven to Port Clyde to find a land line for my radio interview, the boats around us are clear blips on our radar. We do have a moment when the ferries to and from Carver’s Harbor pass right in front of us as we emerge into their ‘lane’, their own deep horns signaling each other with little attention for us as they approach. The sound bounces around in the fog, leaving us feeling that they are all around us, on top of us. They seem to pass close, according to the radar, but they never loom out of the grey curtains. Our own position is clear from the GPS, and the buoys appear with reassuring regularity. These two machines have taken the anxiety out of fog work, for sure, and who wants it back? But it has removed the satisfaction of well-done dead reckoning course work as well.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: