Everyday entropy: GPS grounding

0-0-2-Clipper 6-Clipper-0-0-Cork-1.jpg.gallery
Clipper wreck

FILE : CV4 aka CORK FILE NO. : 100163/RH REFERENCE : REGISTRAR OF SHIPPING, JERSEY SUBJECT : GROUNDING & SUBSEQUENT LOSS DATE : 24TH JANUARY 2010 1. INSTRUCTIONS Instructions were received on 16th January 2010 from the Registrar of Shipping, Regulatory Service, Jersey (the Flag State 1 ) regarding the grounding and subsequent loss of the vessel “CV4”, Registration No. 737-69, on 14th January 2010.

PRINCIPAL CAUSE OF GROUNDING

On the morning of 14th January when CV4 was approaching Gosong Mampango the wind was about 30 knots with moderate to rough seas. The radar was in use however was not obtaining a target. Soundings are relatively sparse and between 30m – 45m, with no banks to indicate close proximity to the reef. The Race waypoint was the light & Racon beacon on Gosong Mampango. The alter-course waypoint as decided by the Skipper of CV4 was approximately 1 mile 0900 (T) from the light. The course, from the south-west (0510 (T) had CPA 0.6 miles on the SE corner of the reef. The chart indicated that there was a steep drop-off from the reef. Navigation was being carried out using the electronic charts. These included details of the largest scale chart but, as far as I determined, not all the warnings outside the border of the chart. There are two principal paper charts for the area where CV4 grounded, 2872, Selat Karimata and Approaches and 3757, Gosong Aling to Pulau Pesemut. These were not provided. There is also a much smaller scale chart, 941A. This was the back-up chart provided in case the electronic chart system failed. The electronic chart contained details of the largest scale paper chart. However the second-largest scale paper chart, 2872, Scale 1:500,000 has been modified since the original print and is WGS84, that is, GPS positions can be plotted directly onto the chart. However the largest scale paper chart, 3757, Scale 1:250,000 is not WGS84 and there are warnings on the upper edge of the chart outside the border. My investigation revealed that these warnings were apparently not included on the electronic charts. All electronic charts were updated prior to departing from Geraldton on 10th January 2010. The paper chart, BA941A, last correction was 20093799 . Maritime Claims & Services Pte. Ltd. Page 22 of 28 The paper charts had the following cautions: CHARTS 2872 AND 2873 POSITIONS Positions on chart 941A differ from those on charts 2872 and 2873 by varying amounts; positions should be transferred by bearing and distance from common charted objects, not by latitude & longitude. CAUTION: SATELLITE-DERIVED POSITIONS Positions obtained from satellite navigation systems, such as GPS, are normally referred to the WGS84 Datum. The differences between the satellite-derived positions and the positions on this chart cannot be determined; mariners are warned that these differences MAY BE SIGNIFICANT TO NAVIGATION and are therefore advised to use alternative sources of positional information, particularly when closing the shore or navigating in the vicinity of dangers UNCHARTED DANGERS: Mariners are warned to exercise caution when using this chart as uncharted dangers may exist due to inadequate depth information. The aids to navigation within Indonesian waters are reported to be unreliable. They may be missing, unlit or out of position. Additionally the largest scale paper chart (3757) has the warning: POSITIONS: Gosong Mampango Lighthouse(30 35’S, 1090 10’E) approx.) and associated reefs Karang Batuan, Karang Sembar and Gosong Kelumpang, were reported to lie0.9’ further east in 1992. Gosong Aling lighthouse (30 31’S, 1100 11’E approx.) and the associated reefs were reported to lie up to 2 miles further eastnortheast. A comparison of the position of Gosong Mampango on the 2 largest scale paper charts (not provided on board however included in the Electronic Charts) is as follows: 3757 Scale 1:250,000 Racon 30 34.6’S 1090 10.2’E 2872 Scale 1:500,000 Racon 30 34.8’S 1090 10.9’E (WGS84) On the electronic chart it was visually apparent that when the scale was changed the reef position moved. There are common rules of seamanship that have been developed as innovations and advances in navigation have been made. These are incorporated in various publications. One such publication (Bridge Procedures Guide) states: Maritime Claims & Services Pte. Ltd. Page 23 of 28 “On charts whose survey source data is very old, the accuracy of those charts may be poor in certain areas: under these circumstances the OOW should not totally rely on position fixing using electronic systems, and should where possible use visual and radar navigation techniques to maintain safe distances off the land.” Chart 941A was published on 11 November 1867. Although upgraded since that time the basic chart and many of the reefs remain as charted 150 years ago. The electronic charts have been developed from the paper charts and reproduce any inaccuracies. There was no way of checking the position during the early morning hours of 14th January. There was no moon at this time (neap tides), no significant change in the soundings that would indicate a line of position and a heavy sea that would likely produce enough clutter to obscure a small echo from the reef. It would have been prudent seamanship to have 2 alternate waypoints on the Chart; a daylight waypoint and a darkness waypoint. The latter would be (say) 10 miles to the east of the reef. However there was one waypoint for daylight and darkness and that was 1 mile from the reef. As it eventuated the reef was between one-half to one mile to the east of the charted position. The reef is approximately one-half mile across. Although the yacht was initially believed to have grounded on the east side of the reef it was later visually confirmed by the skipper to be grounded on the west of the reef in GPS position Lat. 30 34.683S Long. 1090 10.583E. The light/Racon is sited in the middle of the reef and its geographical position as shown on the chart is Lat. 30 34.678S Long. 1090 10.102E. However its position varies from chart to chart as noted in the previous page. The substantial difference on the charts is principally that one chart has corrected to WGS84, that is, GPS positions can be plotted directly onto the chart and the other is originally charted by the hydrographers without the benefit of satellites. Maritime Claims & Services Pte. Ltd. Page 24 of 28 Whilst this is a significant charted error, when taking into account the navigational instruments available in 1867 this error is not surprising. Furthermore it is clearly pointed out in the warnings on the charts.

The principal causes of the grounding and loss of CV4 were – Total reliance was placed on electronic navigation. No second system of navigation was used to verify positions obtained from the GPS – Total reliance was placed on the chart, even though the survey source data was very old – Warnings regarding GPS positions and chart accuracy were disregarded, even though they clearly indicated that the charts were unreliable – The position of the reef on the chart was inaccurate, approximately 1000m east of the charted position – The navigation light and the Racon beacon were not working. (Warnings on the chart advised that the aids to navigation within Indonesian waters may be missing, unlit or out of position) – The electronic charts did not appear to contain the warnings that were shown on the borders of the largest scale paper chart, which should have alerted the skipper to the fact that Gosong Mampango was almost a mile to the east of its charted position – When the light and Racon beacon were not raised visually or on the radar no precautions were taken

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