Many years ago, on my first Atlantic crossing, the only electronic instrument on the boat was an ancient and very
temperamental radar. It seldom worked,
and when it did, it used prodigious
amounts of electricity. Our battery-charging options were limited, so most
A magnetic compass may be old technology, but it’s still an essential navigational tool
of the time it stayed switched off, only
being brought into service in thick
weather or when we were in busy shipping lanes. Navigation was done with
a trailed taffrail log, sextant, and chart.
But the most useful item on board was
the magnetic compass. Sometimes we’d
go for days without getting a reliable
sight, so we relied on dead reckoning,
using the compass course steered and
the distance run to estimate a position.
Information about prevailing currents
and wind direction also helped.
Compasses come in all shapes and
sizes, but for the purpose of this article,
let’s concentrate on the main magnetic
steering compass and leave discussion of
hand-bearing compasses, gyrocompass-es, and other types for a future article.
A low-tech necessity
Compasses, used on boats for centuries,
work because a permanently magnetized
needle always points to north, irrespective of the position of the boat. Many
boaters think that, in these days of modern electronic-charting aids, compasses
are no longer needed. Nothing could be
further from the truth. A magnetic compass requires no electricity to operate, so
it could be the one piece of navigational
equipment that still operates on your
boat when the proverbial you-know-what hits the fan.
As the boat turns, the compass continues to point at magnetic north, and
the course is shown (relative to magnetic
north) in reference to a line, which represents the boat’s heading. A compass
has what is known as the “card,” divided
BY MARK CORKE
This exploded view
of a typical steering
rods that can be
adjusted to reduce