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A Two-Component Electromagnetic Ship's Log

Published online by Cambridge University Press:  18 January 2010

M. J. Tucker ,
N. D. Smith ,
F. E. Pierce  and
E. P. Collins
M. J. Tucker
Affiliation:
(National Institute of Oceanography)
N. D. Smith
Affiliation:
(National Institute of Oceanography)
F. E. Pierce
Affiliation:
(National Institute of Oceanography)
E. P. Collins
Affiliation:
(National Institute of Oceanography)
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Extract

A ship's log is described which works on the principle of electromagnetic induction. The measuring head contains a coil with a vertical axis and is arranged so that voltages are picked up proportional to the two components of water flow past it. The electronic circuits are designed to give a true and stable zero by using a low-frequency squarewave energizing current. Laboratory tests show the output to be linearly related to water velocity. Because of the complicated flow patterns round a ship, the log must be calibrated in situ at sea. Calibration of the forward component meter follows the usual procedure and this meter is accurate to about ±0·1 knot or ± 1 per cent, whichever is greater. However, calibration of the athwartship component meter is difficult and time-consuming, and the sensitivity is dependent on forward speed. With care, it seems that an accuracy of ±0·2 knot or ± 10 per cent, whichever is greater, should be possible with this meter, but more experience of such calibrations is required. The paper is discussed on p. 319.

Type
Research Article
Information
The Journal of Navigation , Volume 23 , Issue 3 , July 1970 , pp. 302 - 316
Copyright
Copyright © The Royal Institute of Navigation 1970

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References

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