Errors in Interpretation
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12. Errors of Interpretation
I M O
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12.1. False interpretation of data:
- ignoring overscale of the display,
- uncritical acceptance of own ship's position,
- confusion of display mode,- confusion of chart scale,
- confusion of reference systems,
- different modes of presentation,
- different modes of vector stabilisation,
- differences between true north
and gyro north (radar),
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Dangerous scale on the display
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dKart
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dKart
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12.2. Avoidance of false interpretation:- the same data reference system,
- appropriate chart scale,
- using the best suited sensor to the given
situation,
- entering the correct values of safety data,- display categories,
- proper data selection.
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The own-ship safety contour: The contour related to the own ship
selected by the mariner out of the contours provided for in the SENC,
to be used by ECDIS to destinguish on the display between the safe
and the unsafe water, and for generating anti-grounding alarms.
If the safety contour selected by the mariner is not available in the SENC, the
ECDIS should select the next deeper contour and inform the mariner.
If, when the ship moves onto a new chart, the safety contour previously in use is no
longer available or the units of depth change, the ECDIS should again select the
next deeper contour, and inform the mariner.
IHO S-52 App.2
The own-ship safety contour, selected from among the contours inthe SENC, is double coded by thic line and a prominent change in
depth shade.
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The own-ship safety depth is intended as an aid when no appropriate
safety contour is available in the SENC.
Soundings equal to or less than the safety depth selected by the
mariner are made more conspicuous than deeper soundings.
A separate set of sounding figures is provided in the PresentationLibrary
Isolated dangers (small shoals, rocks, wrecks, obstructions) of depth
less than the safety contour, and also lying within the safe water
defined by the safety contour, are highlighted by a special symbol.
IHO S-52 App.2
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Guard Vectorto set an advance time (from 1 to 15 min) for
triggering of an alarm as the vessel is approaching a Safety Contour
or Special Purpose Areas.
Guard Vectorvector displayed on the screen from ships position,
graphically presents the approach time to the Safety Contour ordeclared Special Purpose Areas.
NaviSailor 2500 of Transas Marine
Guard Ring to set the approach distance (from 0.1 to 8.0
miles) to the Isolated Danger, whether on an electronic or userchart, for the advanced triggering of an alarm.
Guard Ring ring displayed on the screen around ships position,
graphically presents the approach distance to the Isolated Danger.
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Guard Vector and Guard Ring display
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The expected learning outcome is that the trainee is able to:
1. explain the errors of interpretation due to:
- different modes of vector stabilization,
- overscale of the display,
- uncritical acceptance of own ship's position,
- confusion of reference systems,- different modes of presentation,
- automatic track-keeping features such as the continuous display of
own ships position on the preplanned track,
- differences between true north and gyro north (radar),
2. avoid errors of interpretation by verifying the selection of:- the same data reference system,
- the appropriate chart scale,
- the sensors best suited for the given situation,
- safety values,
- display categories.
12. Errors of Interpretation
