Electronic Navigation

GNSS Integrity and Datum

GNSS positions are usually referenced to WGS84, but charts may have a different or imperfect datum. Modern UKHO charts are normally compatible, yet older charts, harbour plans, and some f...

• Most GNSS positions use WGS84
• Check chart datum warnings

Chart Plotter Route Checking

Audit the whole route at an appropriate larger scale that reveals the available source detail, then compare the display scale with the chart data's compilation or source scale. Zooming in...

• Check the whole route at large scale
• Zoomed-out screens hide dangers

Electronic Charts

An Electronic Navigational Chart is official vector data produced to IHO standards for use in a type-approved ECDIS. A Raster Navigational Chart is official raster data for the relevant a...

• ENC: official vector chart data
• Raster chart: image-style chart display

Alarms and Waypoint Management

Electronic alarms are useful only if they are configured sensibly and understood by the crew. Cross-track error, depth, anchor, AIS CPA/TCPA, arrival, and guard-zone alarms can all reduce...

• Set alarms deliberately before departure
• Avoid alarm fatigue

Radar Set-up and Tuning

Radar performance depends on the set-up. Range scale, gain, sea clutter, rain clutter, tuning, heading alignment, and display mode all affect what you see. A poorly tuned radar may miss s...

• Use an appropriate range scale
• Tune gain and clutter controls carefully

Radar Fixing and Parallel Indexing

Radar range is generally treated as more accurate than radar bearing on a correctly set-up small-craft set, but neither measurement is error-free. One range gives a circle of position; a...

• Radar range is often more accurate than radar bearing
• Use two or more ranges for a radar fix

Collision Assessment with Radar

A target whose bearing does not appreciably change while range decreases is a strong collision-risk warning. Risk can still exist when the bearing changes, particularly at close range or...

• Constant bearing and decreasing range means collision risk
• CPA: closest point of approach

AIS CPA and Limitations

AIS broadcasts a vessel's identity, position, course, speed, and other data. Plotters can calculate CPA and TCPA from AIS targets, making AIS extremely useful for identifying ships and pl...

• AIS helps identify traffic
• CPA and TCPA support early collision assessment

Failure Planning and Redundancy

A Yachtmaster passage plan should include what happens if the plotter, GNSS, radar, AIS, depth sounder, log, or charging system fails. The answer may be paper chartwork, backup handheld G...

• Plan for electronic failure before departure
• Carry backup position and plotting methods

Sensor Independence and Common-Mode Failure

Two displays are not necessarily two independent sources. A chart plotter, AIS overlay, DSC radio, tablet, and autopilot may all receive position from the same GNSS antenna or network. If...

• Several screens may repeat one sensor and one error
• Identify the source, power, network, and failure mode behind each value

Safety Depth, Contours and Display Configuration

A vector-chart display is a filtered view of a database. Safety depth, safety contour, shallow contour, deep contour, category layers, and scale determine which dangers are emphasised. Sm...

• Derive display settings from draught, UKC, tide, squat, and uncertainty
• Know how the fitted plotter selects and displays contours

Worked Radar Closing Assessment

A contact bears 045° relative at 6.0 NM. Three minutes later it still bears 045° relative but is at 5.0 NM. The near-constant relative bearing and decreasing range indicate collision risk...

• One nautical mile closed in three minutes equals 20 kn relative closing speed
• Five nautical miles at 20 kn gives a nominal 15-minute zero-range time

Restricted Visibility: Evidence, Rule 19 and Command

In or near restricted visibility, safe speed and a proper lookout are the starting conditions, not optional responses after a target appears. Have engines ready for immediate manoeuvre, d...

• Rule 19 governs vessels not in sight in or near restricted visibility
• Use safe speed, lookout, lights, signals, engines, radar, and position evidence together

GNSS Anomaly and Spoofing Response

Warning signs include an unexplained position jump, impossible course or speed, several vessels appearing displaced from radar echoes, a charted buoy shown on land, loss of time agreement...

• A plausible display can still contain a false GNSS position
• Protect sea room and disengage position-dependent automation first

Electronic Watch Handover and Configuration Control

A watchkeeper needs more than the active waypoint. Handover should cover the current fix and its evidence, course and speed, cross-track trend, next alteration, traffic and CPA concerns,...

• Handover the evidence, limits, alarms, defects, and call-the-skipper triggers
• Log route and sensor changes that alter the navigation picture

Yachtmaster Offshore Standard: Electronics

A Yachtmaster answer should begin with the vessel, not the screen. State the last position and time the team accepts, identify which data paths now conflict, and explain the immediate act...

Advanced Scenario Check

A fictional yacht is approaching a narrow entrance at night. GNSS and the copied route are suspect; one AIS target has stale manual dimensions; radar shows a second unlabelled echo; depth...