Maritime log


How would seafarers measure their speed at sea?

In the past, explorers, nomads, and other seafarers had to navigate the sea for long periods of time, without spotting dry land on the horizon.

Over the years, seafarers developed different and varied ways of navigating the oceans. Starting with training homing pigeons to find land, using celestial navigation with the help of stars, measuring the angle of the sun relative to latitude, and more. As ships became more advanced, the length of sea voyages could increase, and with them the need to accurately plan the course and establish the position at sea. Otherwise, the stocks of food, medicine, and supplies would run out, sometimes while still at sea, with no assistance available. In order to improve navigation capabilities, a simple measurement tool was invented, called a chip log. The chip log was made of a small wooden board with a lead weight on one edge that caused it to float upright in the water. Attached to the board was a long rope knotted at regular intervals. To begin measuring speed, the sailors would cast the wooden board into the water, and at first contact with the surface, an hourglass on deck was flipped over. Sailors counted the number of knots that passed through their hands until the sand in the hourglass ran out to calculate the relative speed of the ship. The number of knots counted was recorded in a special book called a log, which is why ship records today are still called logs and speed at sea is measured in knots.

Since then, the field of marine navigation has improved dramatically, and automated satellite systems can track, at any given time, the location of a ship at sea. And if you ever do find yourself lost at sea, without satellite reception, you can always improvise a speedometer from a small piece of wood, a rope, and a stopwatch, and navigate to your desired destination.

Translated by Daphna Shapiro Goldberg