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Marine Chronometers Overview

Marine Chronometers Overview

A marine chronometer, also known as a deck watch or a captain’s watch, was initially designed as a precision timepiece used by seamen to locate the exact ship position in the pre-GPS era. Its basic function was in determining the longitude by comparing the Greenwich Mean Time (GMT) and the time at the current location based on positions of celestial bodies.

In order to identify the vessel geolocation in the open sea, the ship captain was supposed to know its current latitude and longitude. Whereas the latitude could be measured by the angle of the sun from the horizon in the Southern hemisphere (and the angle of the Polar Star in the Northern hemisphere), the longitude calculations required a time standard. Thus, the absence of a precise chronometer aboard made navigation more complicated and led to numerous ship wrecks and loss of lives. Therefore, the invention of the marine watch became a real breakthrough and enabled ship crews to navigate their vessels effectively during long sea voyages.

The first mention of a marine chronometer dates back to 1530, when Gemma Frisius, a Dutch scientist, proposed to employ a timepiece to determine longitude. The next effort in deck watch development is attributed to another Dutch physicist Christiaan Huygens, who invented a chronometer using a balance wheel and a spiral spring instead of a pendulum in 1675, however his clock turned out to be inaccurate at sea. Another futile attempt belongs to Jeremy Thacker and Henry Sully, whose clock was unable to keep precise on the shipboard.

John Harrison, a British carpenter, is deemed as the ‘Father’ of a precise marine chronometer. His first two prototypes H1 and H2 were introduced to public in 1735 and 1741 respectively. The clock design represented a pair of spring-connected counter-oscillating beams, so that the structure was not influenced by gravity or ship motion. However, its design was sensitive to centrifugal force, which still made the clock not accurate enough at sea. His H3 version, released in 1759, was equipped with circular balances and caged roller bearings, but was still imprecise. His fourth and the most accurate H4 timepiece model looked like a 12cm pocket watch and was provided by a fast-beating balance wheel controlled by a temperature-compensated spiral spring. This chronometer is known as the first one, which was successfully employed for longitude measurement aboard Aurore ship in 1767.

However, Harrison’s timepiece concept was not the only solution of the precision problem. The alternative pocket watch design was presented by Ferdinand Berthoud and Thomas Mudge. But the greatest step forward in development of marine chronometers was made by Thomas Earnshaw and John Arnold in 1780. The key improvements consisted in simplified spring detent escapements and modified balance spring design, which were successfully employed in deck watches until the electronic era.

Despite the different chronometer designs, all the deck watches possessed a set of the following common features: high accuracy, large dials and bold hands for better readability in poor lighting conditions, and water and shock-resistant cases to withstand the harsh sea conditions, like humidity, temperature changes and vibrations.

During the past two centuries marine chronometers were produced by a number of prominent European watchmakers, including The Marine Chronometer Company and E. Dent & Co Ltd (Great Britain), Mühle-Glashütte, WEMPE GMBH & CO and Feingerätebau K. Fischer (Germany), Autonautic Instrumental (Spain), Ulysse Nardin, Buser Frères & Cie S.A. and H. Moser & Cie (Switzerland). It is curious, that the Buser’s model is featured by John Harrison’s portrait on its caseback.

Now that the Global Navigation Satellite System has firmly entered our daily lives and there is no need for mariners to use chronometers to determine a geolocation, these vintage timepieces are still pursued by true watch collectors all around the world.