ECDIS exam preparation pays off when you treat the display as a connected system: contour values derived from draft and under-keel policy feed the route check, ENC quality categories set your margins, and every alarm gets a reasoned disposition rather than a silenced sound. Work through the two scenarios, complete the settings-sheet exercise, and score yourself against the rubric before considering yourself ready.
Four Contour Settings That Do Different Jobs on Screen
Safety contour, shallow contour, safety depth, and deep contour are four separate settings. Learn what each one controls visually, then derive the values from your draft, under-keel allowance, and predicted tide for each leg.
The safety contour is the depth boundary ECDIS highlights and alerts against when the route or own ship crosses it. The shallow contour sets the boundary of the lightest blue shading band, the deep contour separates the two deep shades, and safety depth is a filter that dims soundings deeper than the value you enter. They look similar on screen but do different jobs: only the safety contour triggers crossing alerts, and only safety depth changes how individual soundings are rendered.
Derive the values from your actual condition: maximum draft for the leg, added squat at service speed, and the under-keel allowance your company policy requires. Then check the ENC itself: if no contour exists at exactly your computed value, ECDIS selects the next deeper available contour, which can shift both the picture and the alerts. Confirm which contour was actually selected in the display settings, and record the reasoning per leg rather than reusing one number for a whole voyage.
| Setting | What it controls | Typical input basis |
|---|---|---|
| Safety contour | Highlighted boundary plus crossing alerts for route and own ship | Draft + squat + required under-keel clearance |
| Shallow contour | Boundary of the shallowest shading band | Same family of inputs; often set near the safety contour |
| Safety depth | Dims soundings deeper than the entered value | Chosen so soundings near your requirement stay visible |
| Deep contour | Boundary between the two deep shading bands | Orientation value; usually well below operational concern |
Reading ENC Quality Data Before Trusting the Picture
ENC reliability varies cell by cell. Zone-of-confidence categories, source diagrams, and the overscale pattern tell you how much the plotted picture can be trusted before you plan distances off dangers.
Every ENC cell carries a category of zone of confidence (CATZOC), shown in a quality-of-data diagram for the cell. Category A1 means the tightest survey accuracy, A2 and B progressively looser, C the loosest assessed category, and U means unassessed. The category bounds how far a charted feature may sit from its true position, which is exactly the margin you need when deciding how far off a shoal or obstruction your track and corridor should pass.
Two other quality cues deserve the same habit. The source diagram shows which surveys produced the data and how old they are, so you can see where depths come from an old lead-line sweep rather than a modern full-coverage survey. The overscale pattern appears when the display scale exceeds the cell's compilation scale: zooming in enlarges the geometry but does not add detail. Treat both as instructions to widen margins and cross-check with radar, not as cosmetic quirks.
| CATZOC category | Meaning for planning | Practical response |
|---|---|---|
| A1 / A2 | Tightest position and depth tolerances from modern surveys | Standard margins from your under-keel policy |
| B | Moderate tolerances; older or less complete surveys possible | Widen distances off dangers; favor radar cross-checks |
| C | Loose tolerances; large positional and depth uncertainty | Generous margins; treat charted details cautiously |
| U | Quality not assessed | Plan as if unverified; confirm by independent means |
Where Route Checking Fits in the Four Planning Stages
Passage planning has four stages: appraisal, planning, execution, and monitoring. ECDIS supports each differently, and the route check is the planning-stage tool that tests the track before you ever load it.
Appraisal means gathering the ENCs, notices, tide information, and port instructions you need. Planning means building the route with waypoints, cross-track limits, and the settings from your computations. Execution means loading the route and confirming settings at handover or before a critical leg. Monitoring means watching cross track, schedule, and alerts underway. Sorting every menu function into its stage keeps your study of the system organized instead of a list of disconnected buttons.
The route check predicts problems before departure: it tests the track against the safety contour, against no-go areas you have drawn, and against your cross-track limits, which define a corridor of acceptable deviation either side of the track. A meaningful check also reviews wheelover positions, abort points, and the scheduled arrival at critical points against tide windows. Run the check after every route edit, because a single dragged waypoint can invalidate an earlier clean result.
Worked Scenario: A Route Check Full of Contour Crossings
A route check that floods you with crossings is asking you to re-examine the plan, not to lower a setting. Walk one crossing end to end: confirm the depth requirement, check the tide window, then decide.
Suppose your maximum draft is 10.0 m, squat adds 0.5 m, and company policy requires 1.0 m under-keel clearance, so your safety contour computes to 11.5 m. The approach ENC carries contours at 10 m and 15 m, so ECDIS selects 15 m as the next deeper available contour, and the route check flags a crossing at the river mouth. The tempting move is to reset the safety contour to 10 m so the alarms stop.
The better decision keeps the plan honest: verify the predicted tide at the planned transit time, confirm that total depth supports the 11.5 m requirement with the stated clearance, adjust the ETA if it does not, and mark the shallow patch as a no-go area so the corridor reflects the hazard. Disposing of the alert by lowering the setting hides exactly the risk the check was built to surface. Record the disposition and the tidal window in the passage plan notes.
Alarms, Cautions, and Sensor Inputs You Must Validate
ECDIS separates alarms, which require action; cautions, which flag conditions needing attention; and indications, which report status. The picture itself depends on position, heading, and speed inputs that need independent validation.
Learn the alert vocabulary for your equipment class, because the same on-screen event can present as a repeating audible alarm on one system and a quiet caution on another. Acknowledgment stops the sound; it never resolves the underlying condition, which keeps running until the cause is fixed or the condition clears. The alert log remains as your record, which is why a written disposition for each alarm is a habit worth building long before any assessment.
The displayed picture is a composite of position, heading, and speed inputs, so sensor validation belongs in your monitoring routine. Compare the electronic position against radar ranges to charted objects, watch for datum-related warnings when older references are in play, and check that gyro heading, course over ground, and the charted track agree during steady steaming. A single offset sensor can draw the entire picture consistently wrong, which is far harder to notice than a frozen or blank one.
Worked Scenario: Overscale Display at Close Quarters
Close-quarters maneuvers magnify every positional uncertainty in the ENC. Before a berth approach, check the compilation scale, the zone-of-confidence category, and whether the features you steer by are visible on radar.
Picture an approach planned at a display scale of 1:6,000 over a harbor cell compiled at 1:25,000, category B. The overscale pattern shows on screen, but the rendered breakwater and buoy positions look crisp, and the plan places a wheelover 0.2 nautical miles off the buoy. The plausible mistake is treating those smoothly drawn symbols as survey-grade positions simply because the rendering looks sharp at large scale.
The better decision acknowledges what overscale means: the geometry has been enlarged, not resurveyed, and a category B cell permits positional slack that matters at close quarters. Confirm the buoy by radar before committing to the wheelover, keep the approach inside the corridor you checked at the compiled scale, and note the overscale condition in the plan. If radar and display disagree, stop and reconcile the difference before making the turn, not after.
A Preparation Sequence, a Settings-Sheet Exercise, and a Rubric
Cycle your preparation through display setup, route building, and monitoring drills, and grade each cycle against a written rubric. Readiness means every alarm has a reasoned disposition, not a silent bridge.
A realistic four-week sequence, adaptable to your available hours: week one, build a settings sheet for one port approach, computing contour values from a stated draft and under-keel policy; week two, create and check the full route, including no-go areas and cross-track limits; week three, run monitoring drills, introducing sensor faults on a trainer or on paper and diagnosing them from their on-screen behavior; week four, integrate everything into one timed scenario with a written alarm log.
For the exercise, re-run your scenario after a week and audit the alarm log: every entry should show the condition, the decision, and the justification. Score one point each for settings traceable to draft and policy, no-go areas marked at genuine hazards, cross-track limits consistent with the waterway, overscale and CATZOC margins noted in the plan, and dispositions written for every alarm. Five points is a learning milestone you set for yourself, not a prediction of any result.
- You can state, for any leg, why each contour value was chosen and which ENC contour ECDIS actually selected.
- You can explain the difference between an overscale display and a denser survey without consulting notes.
- Your route-check log shows no unresolved alarms before the simulated departure.
- You can describe how a wrongly offset position input would present on screen and how you would detect it.
- Your scenario paperwork includes a stated draft, policy, and tide assumption behind every number.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.