of helm in the half ahead condition are shown in Figures 4 and 5.

The availability of such velocities in real time could have important implications for modulating the paths of large vessels when disabled, as accurate and instantaneous feedback can be used to apply relatively small forces to keep a vessel from intercepting a charted object, providing sufficient time is available, as for instance in the case of the BRAER.

Figure 5: Container Ship Trials - Speeds F&A
and Athwartships at For'd and After Sensors

The predictive output of a rate aided mathematical model could have important implications for the piloting of vessels. There are indications that such models could provide relatively accurate predictions of position for several minutes into the future. This assumes that data about helm and engine setting is also available in real time.

These outputs are based on the phase change of the carrier rather than being derived from Code Phase modulation processing. As such they can also yield a certain redundancy in relative position determination or alternatively can be used as filters for providing a higher reliability of position finding, particularly in ports and harbours where the GPS position may be compromised by proximity to high land.

Conclusions

GPS derived outputs have a valuable role to play in the management of sea going craft. While current standards of available outputs may leave something to be desired in terms of accuracy

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