Equipment Guide · ECDIS
ECDIS puts an official vector chart and your live position on one screen — and because the chart is data, not a picture, the machine can check the water you haven't reached yet. But it only checks against the numbers you give it: safety depth, safety contour, look-ahead. Tap a step or press "Play" to follow the chain from the sensors to the alarm — then take the simulator, set your own safety contour, and see what happens when it is set right, set too deep, and set too shallow.
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You work out a safety depth of 14.5 m (draught 12.0 + squat 1.0 + UKC 1.5) and type it in. The ENC only carries the contours the surveyors drew — here 5, 10, 20 and 30 m — so the system takes the next deeper one and puts the 20 m contour in force. That is the machine protecting you, and the first habit is simply to check which contour it actually selected. The second habit matters more: 20 m paints a lot of coastal water blue and fires a lot of alarms, and the temptation is to override the contour down to 10 m to quiet the screen. Do that and everything between 10 m and your 14.5 m need — water that can put the ship aground — is displayed as safe and crossed in silence. Real ships have grounded exactly this way, with ECDIS working perfectly.
Press Start to run the approach — set the contour honestly and alter for deep water when the alarm comes; then Reset, drop the contour to 10 m “to cut the blue”, and watch the machine stay silent all the way to the putty.
About the simulator
The ship is running toward a charted 11 m shoal (time runs ×120). The section shows what the water is really doing; the small inset shows what ECDIS paints with your settings. Company policy needs draught + 2.5 m of water (UKC + squat margin). Set the safety contour, watch the guard zone, and when the alarm comes, alter for deep water — then reset, set the contour to 10 m "to cut the blue", and watch the machine stay silent all the way to the putty.
Charted contours in this ENC — 5 · 10 · 20 · 30 · 50 m. Your typed value rounds up to the next of these; the "contour in force" gauge shows what the machine is really checking. Shoal ahead 11 m · company need = draught + 2.5 m.
UKC = depth − draught − squat, and squat grows with the square of speed (V²/100 in open water) — slowing down buys clearance instantly. The alarm fires when the guard zone touches water shallower than the contour in force — not shallower than your ship needs. Those are only the same thing if you set the contour honestly.
Working principle — explained in our own plain words with our own schematic from general marine knowledge (not copied from any OEM manual). Conceptual; varies by ship/model. Reviewed and verified by a Master Mariner.