Definition

Noun: A patent log is a specific type of nautical instrument, typically cigar-shaped, equipped with rotary fins (or a propeller). It is towed behind a moving ship to measure the vessel's speed through the water and, by extension, the distance traveled.

Usage

The term patent log is used exclusively as a compound noun to refer to this historical mechanical device. It is a technical term from maritime navigation.

Examples

• The sailor deployed the patent log from the stern to calculate the ship's speed.
• Before modern electronic systems, the patent log was an essential tool for navigation.
• The captain checked the reading from the patent log to estimate the distance covered during the watch.

Advanced Usage

• The device is also known historically as a taffrail log, as it was often deployed from the ship's taffrail (the rail around the stern).
• The operation involves noting the rotation count of the fins over a timed interval, which is then converted into knots (nautical miles per hour).

Variants and Related Words

• Chip log (or common log): An older, simpler predecessor to the patent log, using a weighted wood chip and a knotted rope.
• Pitometer log: A later type of ship speed indicator that uses water pressure.
• Electromagnetic log / Doppler log: Modern electronic methods for measuring speed through water.

Synonyms

• Ship's log (in the specific context of a speed-measuring device)
• Taffrail log
• Mechanical log

Notes

• Patent log is a fixed compound term. The word "patent" here refers to the device being a proprietary, invented mechanism, not to the legal concept of intellectual property.
• It is distinct from the general term "logbook" (a record of events), though the data from the patent log was recorded in the ship's logbook.

Noun

1. a cigar-shaped log with rotary fins that measure the ship's speed