patent log

navigational instrument

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Last updated

July 23, 2026

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A "patent log" is a type of taffrail log, which is a navigational instrument used to measure a ship's speed through the water. This instrument works by towing a vaned rotor from the stern of the ship. The revolutions of this rotor are then counted on a register, indicating the speed. While early methods of speed measurement involved dropping a floating object overboard or using a knotted rope with a sandglass, the patent log offered a more advanced and continuously readable method. These logs became more common in the mid-19th century, with significant refinements introduced by Thomas Walker starting in 1861.12

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…Humphry Cole, invented the so-called patent log, in which a vaned rotor was towed from the stern, and its revolutions were counted on a register. Logs of this kind did not become common until the mid-19th century, when the register was mounted on the aft rail, where it could be…
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…Humphry Cole, invented the so-called patent log, in which a vaned rotor was towed from the stern, and its revolutions were counted on a register. Logs of this kind did not become common until the mid-19th century, when the register was mounted on the aft rail, where it could be…
Read More