Towards an Improvement of Magnetic Compass Accuracy and Adjustment

Abstract

Many ship accidents have arisen from an error in course indication. Bearing in mind that the actual errors in gyrocompass and satellite compass are really minor, they may be considered valid to be input into an autopilot provided that any failure in such devices is controlled by means of a secondary heading source such as a magnetic compass. However, magnetic compass deviation may be significant and its heading should be corrected before being input to the autopilot. The errors caused by the geographic variability of the deviation should also be taken into account. Moreover, the current way to reduce the deviation requires that the ship is un-berthed to execute a complete swing. The aim of this article is to obtain a ship magnetic model by means of an algorithm based on least squares to correct magnetic compass heading input in the autopilot and to permit definitive magnetic compass compensation without swinging the ship through 360°.

Determining Residual Deviation and Analysis of the Current Use of the Magnetic Compass

“…If the compass deviation is above this value, the full formulae and the corresponding ship maneuvering method should be used [21]. This theory is also found in other studies [24,33,34]. To be widely accepted, these methods need some additional empirical evaluations and comparisons with the "classical" methods of compensation in the cardinal and intercardinal courses.…”

“…Other authors propose an algorithm to compute the latitude error while the ship is in service somewhere in the world [33]. However, all the listed improvements in compass adjustment activity are based on the ship's existing deviation table.…”

Trustworthiness of Autonomous Systems

“…So, an AS is trustworthy if we can rely on it being right. For example, a binnacle compass is trustworthy if a sailor can rely on it to accurately adjust to the rise and fall of the waves and orient to magnetic north [7]. If a sailor navigates to the wrong shore, she might wonder if her compass has become unreliable and thus she ought not trust it.…”

The Compass Error Comparison of an Onboard Standard Gyrocompass, Fiber-Optic Gyrocompass (FOG) and Satellite Compass

“…Many ship accidents have arisen from an error in course indication. Considering that actual errors in gyrocompasses and satellite compasses are very minor, such devices may be regarded as valid inputs for autopilot functions, provided that any failure in their operations is controlled by means of a secondary heading source [14]. Meanwhile, real information regarding both the character of the oscillations and the dynamics of a compass in real circumstances encounter the problem of separating the natural oscillations of the ship (yaw) from the oscillations of the compass, resulting from its design.…”