Navigation by Estimation
The attention span of the average helmsman working at peak efficiency is 30 minutes, dropping off considerably until four hours, after which he is more a danger than a helping hand.
In a crossing situation with another boat at night, note the other vessel’s position relative to a low star. If the boat and star don’t separate, take evasive action.
Give ’Em the Fingers
The “three-finger rule” says that when an object, such as a lighthouse or tower, appears as tall as three fingers held sideways at arm’s length, it’s about 10 times as far away as it is tall. If the chart says the lighthouse you see is 150 feet tall, when it appears “three fingers” tall you’re about 1,500 feet or a quarter of a nautical mile away from it.
Since sound travels at a known speed, you can tell how far off an object is by timing your echo. Every second of delay equals 200 yards. Use this in fog or at night against cliffs, buildings or even large ships.
Go to the Light
White navigational lights appear first when approaching a shore at night. Red and green lights have about three-quarters of the range of white ones.
Rule of Thumb
Nautical legend has it that the phrase “rule of thumb” came when ship masters never allowed themselves to get closer to an obstacle than the width of their thumb on a chart.
Edge of the Earth
Distances over the water seem greater than on land. When standing eight feet above the waterline, as you might in the cockpit of a cruiser, the horizon is barely 3¼ miles away. At six feet up, it’s only 2½ miles.
A statute mile is the distance a Roman soldier covered in a thousand (mille in Latin) steps, which is now 5,280 feet. By convention, statute miles are used with charts of inland waters and the Intracoastal Waterway. A nautical mile is 6,076 feet, which corresponds to one minute of latitude, and so makes navigation computations easier.