Furuno FMD-3100 Manual page 24

iii. Workaround #3
Four colour pattern is used.
Safety contour is set to the previous shallower depth contour than the safe draft. For example if the safe
depth is 13 metres and the available depth contours are 10m and 20m then the safety contour is set at 10m.
Deep contour is set to the next deeper depth contour than the safe draft. For example if the safe depth is
13 metres and the available depth contours are 10m and 20m then the deep contour is set at 20m.
Shallow contour may be set to any available contour lower than the safety contour.
Safety depth set equal to safe draft and No-Go Areas are drawn manually by the navigator.
Advantages
• Applicable isolated dangers will be shown up to the safety contour depth setting.
• Vessel will sail through 'safe' waters. This might be considered as a disadvantage as more water will
be portrayed as safe than what is actually safe but the advantage is that the navigators are getting
accustomed to how the display should look.
• Safety contour alarm will not sound without it being actually applicable.
• The navigable waters area in this case is narrower and provides to the navigator an extra visual warning
that they are approaching dangerous waters.
• No doubt about the safety of the white area (deep water area in the four colour pattern) as this area is
clearly distinguishable and contains all of the area which is deeper than the deep contour setting.
Disadvantages
• Procedure for setting depth alarm settings (safety depth, safety contour, deep contour, shallow contour)
more complicated than the procedure in workaround #1 and workaround #2
• Area portrayed as safe (area outside the safe contour) does not correspond to reality.
• Safety contour alarm will not sound at the proper depth but will sound at a later stage.
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