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,
offshore thunderstorm has built between you and the dock. What do you do? The decisions you make at this point could literally save your life.
Basic Facts
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.
The Troubling Situation
Here we are, twenty miles offshore, and the offshore thunderstorm 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.
What Happens in an Offshore Thunderstorm
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.
- First, it causes the wind to pick up. As the pressure drops, wind begins to circulate around the system, heading down to the low pressure. In the northern hemisphere, that means a counterclockwise rotation, and the closer the storm gets, the higher the winds become.
- Second, it causes the fish to really turn on. If the air pressure drops, the relative water pressure drops as well. Fish can sense the pressure drop with their lateral lines. Knowing that the seas will soon be churning and dirty, many species, particularly shallow water and bottom fish, will “feed up” before the storm.
- It generally takes a combination of decisions surrounding the existing circumstances that lead to trouble. But fish going into a feeding frenzy, coupled with a decision to wait just “a little longer” are two that can really put a boat in jeopardy.
