📚 This article is part of the “ECDIS Masterclass Series”
Part 1 | Part 2 | Part 3 | Full Guide

⚙️ Part 2 – ECDIS Safety Parameters, CATZOC, and Operational Functions

📊 10. CATZOC – Category of Zone of Confidence

CATZOC represents the accuracy and reliability of survey data used to create an ENC. It indicates how well the depths and positions are known.

CATZOC	Accuracy (Position)	Depth Accuracy	Typical Usage	Symbol on ENC
A1	±5 m + 5% of depth	1 m + 2% of depth	Harbor areas surveyed with high precision	⭑⭑⭑⭑⭑
A2	±20 m + 5%	1 m + 2%	Approaches and coastal areas	⭑⭑⭑⭑
B	±50 m + 5%	1 m + 2%	General coastal areas	⭑⭑⭑
C	±500 m + 5%	2 m + 5%	Unsurveyed or old survey data	⭑⭑
D	Worse than C	Unknown	Poorly surveyed regions	⭑
U	Unassessed	—	Data not evaluated	U

Importance:
When planning a voyage, officers must evaluate CATZOC levels along the route. Lower CATZOC means higher uncertainty, requiring increased under-keel clearance and conservative safety contours.

⚓ 11. Safety Parameters in ECDIS

Safety parameters are the foundation of anti-grounding protection in ECDIS. These settings must be entered correctly before every voyage.

Parameter	Definition	Typical Input / Guidance
Safety Depth	Depth below which navigation becomes unsafe.	Equal to vessel’s draft + UKC (Under Keel Clearance).
Safety Contour	Boundary line between safe and unsafe waters.	Closest deeper contour available greater than safety depth.
Shallow Contour	Defines the area considered definitely unsafe.	Slightly less than safety depth (often draft value).
Deep Contour	Defines deep-water zone used for open-sea passage.	Usually 2 × draft or 30 m minimum.
Cross-Track Distance (XTD)	Maximum allowed deviation from trackline.	Usually 0.3 – 0.5 NM (adjust by area).

safety contour visualization – blue safety contour line separating depths

🔹 Base, Standard, and Custom Display Modes

ECDIS provides multiple levels of chart detail:

Base Display – Minimum required objects always visible (coastlines, safety contour, own ship, scale).
Standard Display – IMO-recommended configuration for normal navigation.
All Display – Shows all chart objects including optional layers.
Custom Display – User-defined selection of layers depending on operation.

⚙️ 12. Safety Depth vs Safety Contour Example

Example Calculation:

If vessel’s draft = 14.5 m, required UKC = 1.0 m,
→ Safety Depth = 15.5 m.

ECDIS will automatically select the next deeper contour (say 20 m) as the Safety Contour.
All depths shallower than 15.5 m will appear in blue; deeper waters remain white, providing an immediate visual warning.

⚠️ 13. Alarm and Indication System

ECDIS alarms ensure navigational safety and alert the officer to potential hazards.

Category	Example Alarms	Action Required
Critical Alarms	Safety contour crossing, deviation from track, danger of grounding	Immediate navigational action
Indications	Display mode change, loss of sensor input, ENC update missing	Informational, verify input
Warnings	Route check errors, isolated dangers nearby	Acknowledge and assess

Important:
Per IMO MSC.302(87), all ECDIS must comply with Bridge Alert Management (BAM) — ensuring alarms are prioritized and audibly distinct.

ECDIS Alarm Panel %E2%80%94 Example Showing Safety Contour And Position Alarms

🧭 14. Route Planning and Monitoring

ECDIS provides two major navigation phases:

🧩 Route Planning

The process of creating a voyage route from departure to destination, considering chart scale, dangers, TSS, and safety settings.

Essential Steps:

Select proper ENC coverage for the voyage area.
Input waypoints — adjust leg types (rhumb line or great circle).
Apply Safety Parameters (depths, XTD).
Perform Route Check for dangers and warnings.
Save and approve route for monitoring.

ecdis route planning screen with waypoints and leg data

🚢 Route Monitoring

During navigation, ECDIS continuously compares own-ship position with the active route.

Functions include:

Real-time position plotting (from GPS or DGPS).
Cross-Track Error (XTE) monitoring.
Safety contour and isolated danger alarms.
Target overlay (AIS & ARPA).
ETA calculation for each waypoint.

🔄 15. Cross-Track Error (XTE) and XTD Setting

Cross-Track Distance (XTD) defines allowable deviation from the route centerline.
If the vessel exceeds the XTD limit, an XTE alarm is generated.

Formula:
XTE = Distance × sin (bearing difference)

Setting XTD depends on vessel size, maneuverability, and navigational area (e.g., 0.3 NM for coastal, 1.0 NM for ocean passage).

🗺️ 16. Map Scales and Over-Scaling Warnings

ECDIS automatically warns when charts are displayed outside the intended scale range.

Over-scale: When zoomed in beyond ENC accuracy.
Under-scale: When zoomed out and chart details disappear.

To maintain accuracy, always use the correct usage band ENC for the navigational phase (Harbor → Approach → Coastal).

✅ Summary – ECDIS Safety Parameters & CATZOC Explained (Part 2)

This section of the ECDIS Masterclass Series focuses on how safety settings and survey accuracy directly affect safe navigation. It explains CATZOC (Category of Zone of Confidence)—the accuracy level of seabed data—and how officers must interpret it when setting safety depths and contours.

You’ll also learn how to correctly configure safety parameters, handle ECDIS alarms, and plan or monitor routes with proper XTD/XTE limits. Real-world examples show how small errors in settings can lead to grounding risks, emphasizing why understanding CATZOC and safety contours is essential before every voyage.

👉 Next: ECDIS Alarms & Safety Contour Settings Explained
👉 Continue with: How to Update ENCs in ECDIS Step-by-Step