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A Complementary High Precision Acoustic Positioning System for Dynamic Positioning Vessels

Morten Berntsen View Supplier Profile

Originally printed in: Exploration & Production: The Oil & Gas Review - 2005

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Field Results Position Reference

The HAIN position reference system has gone through several sea trials on the Kongsberg Maritime vessel Simrad Echo. The trials are carried out for debugging purposes and accuracy analysis. A short trial on an offshore DP vessel also has to be carried out.

Figures 1a and 1b show the vessel position during the test, as logged by the differential global positioning system (dGPS).

Figures 1c and 1d show the dGPS North co-ordinate from the scatter plot on the previous slide. Figure 1c shows the HAIN position in green and the HiPAPpositions in blue. The update rate of the HiPAP positions varies between 20s and 5s. In the last 10.5 minutes there are no HiPAP positions. The update rate of the HAIN positions is 1s. The north axis in the HAIN plot has the transponder position as the origin.

Figure 1a,b,c,d

1. Sails backwards 150m with HiPAP update rate 20s; 2. Stationary with HiPAP update rate 10s and then 20s;
3. Changes heading first CCW 40° and then CW 70°, with HiPAP update rate 20s; 4. Sails a square with HiPAP update rate 20s;
5. Sails a square with HiPAP update rate 5s; 6. Removes the HiPAP position aid from the HAIN for 10.5 minutes.
DP used HAIN as the reference during operation one to five. DP used dGPS as reference during operation six and just logged the drift in HAIN

The north axis in the dGPS plot is in UTM. (If more questions about the axes, tell that UTM north is not the same as geographical north and that an UTM metre is not exactly one metre.)

It can be seen that there are some wild-points in the HiPAP measurements. The position quality assurance (QA) test in the HAIN has rejected these positions in realtime. It can be seen that there is a good correlation between the plots, except during the 10.5 minute interval (6) without position aid. In this interval the vessel is stationary, as shown on the dGPS plot. The unaided HAIN position drifts 50m in a northerly direction, proving that inertial navigation alone is not ideal.

Figure 2: HAIN Position Reference Accuracy Figures

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