Sunday, February 27, 2005

Navigation Past and Present

Bill's Log

When I was a youngster there were three primary aids to marine navigation: A chart, a compass and a lead line.

If the compass were to fail, judging direction would be down to observation – things like comparing the ship’s heading with the position of the sun. Being in the northern hemisphere with the rising sun dead ahead meant the ship would be sailing in an easterly direction. If that course were maintained, by mid-day, the sun would be to the south and at right angles to starboard. That’s all basic stuff, but if land were visible, guesstimates of angular direction in relation to prominent features shown on the chart such as headlands, lighthouses and buoys would be helpful in fixing the yacht’s position and course. Even the observation of transient things like wind and wave direction, and the position of clouds would be of momentary use, as would the stars at night.

The most singular and greatest loss would be the chart. Without it, the sailor would not know what to expect, unless he had sailed those waters before. Would he come to the edge of the world, only to plummet over a precipice? His understanding of the chart, its symbols, scale and orientation would be necessary for him to make best use of the information in preparation for events ahead.

An often forgotten aid to navigation is the depth sounder; in my case I have used a lead and line. By counting the number of fathom markers on the line a precise indication of the depth of water can be found. A lead has a cavity at the bottom which is for tallow (a sticky substance) so that when it comes into contact with the seabed a sample can be retrieved. Knowing if it is sand, mud, shale, gravel or pebbles etc., is useful to help place a ship in a particular spot according to information on the chart. Sadly, modern metric charts give scant knowledge of the nature of the seabed.

Over the years technology has changed the nature of navigation beyond recognition – into what would have been considered the realms of fantasy. Electronic charts, compasses, GPS and radar have revolutionised navigation, relieving the navigator of many tedious calculations and observations. Indeed, such is the state of electronic equipment that the helmsman can allocate the onerous job of hand steering to his robot Autohelm.

I confess to not being a Luddite who defiantly ignores what technology has to offer. As a result life aboard my yacht when underway is much less taxing and so much safer. My GPS is linked to a laptop computer with a large-scale electronic chart clearly indicating the yacht’s position within a few metres. That’s not to say I’ve abandoned ‘real’ charts, the ship’s compass and my faithful lead and line.

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