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Decca Speed Trials

Published online by Cambridge University Press:  18 January 2010

J. Th. Verstelle
Affiliation:
(Hydrographic Office, Royal Netherlands Navy)
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The Decca method of conducting speed trials and its considerable advantages over other methods have been described in this Journal and elsewhere. Decca is nowadays widely and successfully used for acceptance trials (speed, calibration of (Sal) log, turning circles and (crash) stopways) by Royal and Merchant Navy ships of Britain, the Netherlands, France, Denmark, Sweden and probably of other nations.

The results of speed trials of Netherlands Merchant Navy ships are given in the present paper. Those of the equally successful turning circles and stopways are not given here, since their numerical results would be of little interest to the reader; a pictorial representation—among other things allowing for a comparison between various interesting turning habits of different ships—would be more suitable, but would occupy too much space.

Short Description of the Method. Each speed determination consists of 4 to 6 runs, alternatively in opposite directions. In each run 20 photographs of the decometers are taken at 30-second (or, for very high speeds of 30 kt. or more, 15-second) intervals and one single run therefore takes 9½ minutes. Specially calibrated Decca receivers are used to ensure a much higher accuracy than is achieved (and needed) for normal navigational purposes.

With the aid of special, large-scale, Decca charts or special tables, all these decometer readings—80 in 4 runs or 120 in 6 runs—are converted into rectangular coordinates X, Y.

Type
Forum
Copyright
Copyright © The Royal Institute of Navigation 1961

References

REFERENCES

1Verstelle, J. Th. (1953). Methods of conducting ships' speed trials. This Journal, 6, 297.Google Scholar
2Verstelle, J. Th. (1955). Speed trials with the Decca Navigator. This Journal, 8, 41.Google Scholar
3Verstelle, J. Th. (1958). The Decca system for ship acceptance trials, International Hydrographic Review, Vol. XXXVI, No. 1, July 1959 (reproduced from Netherlands Hydrographic News Letter, no. 27, March 1958).Google Scholar
4Versteile, J. Th. (1958). Accuracy of speed trials on the measured mile, International Hydrographic Review, Vol. XXXV, No. 2, November 1958 (reproduced from Netherlands Hydrographic News Letter, No. 28, April 1958).Google Scholar