In order for the navigator to measure the speed of his ship, he devised the (maritime) log. As the first type of log, a simple wood must have been used, which was thrown from the bow of the ship in order to measure how long it would took for it to reach the stern, knowing the distance between bow and stern. In this way, it quickly became apparent that speed was not being measured with accuracy, both because the wood did not remain still due to the waves, but also because the distance was not enough, especially for the small ships. Thus, the first common log was invented in the 17th century, which was left at sea from the stern of the ships. The common log consisted of the spinning wheel, the delta with a pencil below in order for it to stand upright and the floor rope, which was tied up to the delta with the weights.

The log was left in the sea from the stern of the ships, and when the delta was away from the wake of the ship, the knots, which had intentionally been placed on the floor rope, passed through the stern handrail in numbers equivalent to the miles per hour of the speed of the ship. That’s the reason why in terms of the speed of the ship instead of saying ‘’miles per hour’’, we use the term ‘’knots’’. Time was measured with an hourglass.

Following came the more advanced type of mechanical trailer trolley, also known as taffrail log. It was developed in the 18th century, and in the 19th century it replaced the traditional log.

The specific mechanical log, taffrail-type, operates based on physical principles in a way similar to the car odometer. A fin or rotor is towed from the stern with a long rope. As it crawls from the rope to the sea,, its rotational speed turns the mechanism through the rope, which through an indicator shows the speed of the ship.

Since the second half of the twentieth century, the seamen use more modern mechanical and electromechanical versions, the hull odometers, permanently attached to the hull of the ship, which are based on a small propeller or paddle wheel, which is linked with (or through) the bottom of the hull, especially on smaller yachts.