You’re thirty-five miles offshore in a small fishing
boat and there is only one path back to the dock.
The problem is – a big
thunderstorm has built between you and the dock.
What do you do? The decisions you make at this point
could literally save your life.
First, let’s look at some very basic knowledge
regarding offshore fishing or boating – things that
every boater should know.
The visible horizon distance on the water is
about eighteen miles at sea level. For every foot
you can get above the water, you extend the visible
horizon distance. While you may not be able to see
the shore or buildings on land from where you are,
lookouts on a passing ship’s bridge will be able to
see those landmarks. The higher you get, the more
you can see.
The same line of sight rule applies for VHF radio
waves. Short of an atmospheric anomaly called
skipping, VHF radio waves are only as good as a
straight line of sight. Skipping happens as radio
waves bounce off the atmosphere and back to earth,
sometimes several times. Where the waves return to
earth, a radio receiver can pick them up, and
sometimes that is several hundred miles away.
As with the visible horizon, the radio wave,
straight-line distance can be increased by getting
up off the water. A boat antenna needs to be located
at the highest point on the boat. That will extend
the effective distance. Couple that with a shore
antenna that is on a tower, and the radio horizon is
extended a number of miles.
Even with a good antenna, the power driving the
radio wave has to be sufficient to reach a distant
antenna. Anyone going offshore without at least a
twenty-five watt VHF is taking a big chance. Some
boats head offshore with a five-watt hand held
radio, and then wonder why they can’t raise anyone
on a radio check. Some boats take a hand held
twenty-five watt radio with a small antenna,
thinking they are covered. While those radios are
better than no radio, they are insufficient safety
devices with which to head offshore beyond the
visible horizon.
So, here we are, twenty miles offshore, and the
thunder clouds are building. As you judge the wind
and watch the clouds, you can see that the whole
system is heading right at you. In the distance,
lightning bolts are lighting up the interior of the
thunderhead, and thunder rumbles lowly. One thousand
one… one thousand two… one thousand three… You count
the seconds between the lightning flash and the
thunder rumble. Every five seconds of sound delay is
roughly one mile in distance. And still you fish.
Thunderheads that build over land along the shore
are miniature, self contained, low-pressure systems.
As they move toward you the atmospheric pressure
drops, and that drop in pressure does a couple of
things.
