What is a Chronometer?

Written by Amit Sharma

The chronometer is an accurate time keeping instrument carried on board.  It always shows the GMT.

Use of Chronometer Onboard

The primary use of a chronometer on board of a ship is for Astro-Navigation. Sun is the most commonly used heavenly body for this purpose. The altitude of the Sun changes rapidly and  an error of  four seconds can create an error of one nautical mile in the observed position.

Accurate time is also essential for running a ships routine and a chronometer provides such accuracy.Currently the GPS is used for both these purposes, but as an alternate measure, a chronometer is still used.

Types of Chronometers
  1. The Spring Tension Chronometer (winding Type): this chronometer employed a balance wheel and a spiral spring for regulation, instead of a pendulum
    • 2-day variety
    • 8-day variety (So named because of the number of days it would work after winding once. The former is more popular on merchant ships.)
  2. Electronic Quartz crystal chronometerQuartz Crystal Chronometer is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than mechanical clocks.

Errors of chronometer

  • No chronometer is expected to keep perfect time.
  • But if a chronometer gains or loses the same amount each day (i.e., if it has a constant daily rate),
  • Daily rate may change due to temperature variation, vibration, shock, magnetic influence, irregular winding, age, etc.
  • It is suitable for navigation because the precise value of the chronometer error at any instant can be obtained by simple extrapolation.
  • The chronometer error is noted each day at sea by means of radio time signals and the error noted in thechronometer error book
  • A chronometer is landed ashore for repairs or overhaul when
    1. Its daily rate is erratic
    2. Or the daily rate of a spring tension  chronometer exceeds 6 seconds.

History of chronometer

A marine chronometer was a high tech product of its era which can be compared to other landmark inventions like the telegraph, steel making, railways, steamships and so forth. The chronometer was the life work of one man, John Harrison, spanning 31 years of persistent trial and error that revolutionized naval (and later aerial) navigation. The British beat France, Spain, Germany, Holland and Belgium as colonisers of the world because of superiority of the Royal Navy over all other navies. Royal Navy proved to be superior to other navies of the era because they always had a technological edge over the others. The Chronometer was one such invention. British fleets had the surety of navigation given by the chronometer, and their Portuguese, Dutch, and French opponents did not.

About the author

Amit Sharma

Graduated from M.E.R.I. Mumbai (Mumbai University), After a brief sailing founded this website with the idea to bring the maritime education online which must be free and available for all at all times and to find basic solutions that are of extreme importance to a seafarer by our innovative ideas.

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