Module 10 – Nautical Charts & Electronic Navigation

Topic Learning Outcomes

• By the end of Module 10 students should be able to:

  • Construct a position line that clears a charted danger by a specified distance.

  • Demonstrate working knowledge of electronic charts, their components, and safe-navigation applications.

Navigational Hazard Avoidance & General Prompt

• Central guiding question posed several times: “If you are a navigator, how would you avoid dangers or hazards at sea?”

  • Encourages constant situational awareness and proactive passage planning.

  • Sets the stage for using BOTH traditional paper-chart techniques and modern electronic solutions.

True-Course Determination Examples (Visual Problems)

• Multiple slides show Istanbul Strait scenarios:

  • Narrowest point between Kandilli and Asiyan.

  • Compass roses labelled $000^{\circ},\;090^{\circ},\;180^{\circ},\;270^{\circ}$ invite students to deduce the vessel’s True Course (T.C.).

• Follow-up exercise at Yeniköy: sharp turn illustrated; again students must infer the correct $T.C.$.

• Key pedagogical angle: translating chart symbols & geographic references into numeric courses.

Bearing-Error Exercise (Course $032^{\circ}T$)

• Hypothetical: “Your course is $032^{\circ}T$ — what happens if you steer < or > than that?”

  • < $032^{\circ}T$ → risk of drifting port-side into shoal/obstruction.

  • > $032^{\circ}T$ → risk of starboard deviation, possibly traffic-lane violation.

  • Emphasises minute-to-minute correction and monitoring of compass versus intended track.

Concept of Danger / Clearing Bearings

• Definition: Danger or Clearing Bearing = a single position line intentionally drawn so that, provided the vessel keeps the object’s bearing Not More Than (NMT) or Not Less Than (NLT) a stated value, the ship will remain in safe water.

  • Reacts principally to tidal currents, set & drift, and wind.

  • Allows continuous monitoring using hand-bearing compass or radar to verify safety without plotting full fixes.

Inshore Traffic Zones & TSS Illustration

• Slide shows Traffic Separation Scheme (TSS) portions labelled A, B, C with arrows.

  • Yellow lines (except arrowed traffic lanes) likely represent clearing bearings that hug lane boundaries.

  • Navigator must recognise which lines are MANDATORY traffic-flow arrows vs discretionary danger bearings.

Leading Lines (A Special Clearing Bearing)

• Leading Line (transit line of two marks/lights) serves dual function:

  • Maintains vessel in centre of dredged channel.

  • Acts as a danger bearing — deviation = potential grounding.

• Example annotated: “Out of this bearing line … might lead your ship into grounding.”

Worked Method: Constructing & Interpreting NMT / NLT

1. Pick a conspicuous object outside danger (e.g.

   • Lighthouse, Racon buoy, church spire).

2. Identify safe vs danger water on chart.

3. Draw two simultaneous position lines:

   • Course line (track).

   • Bearing line (from vessel to object).

4. Extract numeric values at compass rose.

   • Example: Object bearing $010^{\circ}T$, ship’s course $032^{\circ}T$.

5. Set rule:

   • If instruction is NMT $010^{\circ}T$ → any reading > $010^{\circ}T$ means vessel is being set toward danger.

   • If instruction is NLT $057^{\circ}T$ → any reading < $057^{\circ}T$ is unsafe.

Visual Progression (Danger Increasing)

• Slide 18 (safe): Bearing remains <$010^{\circ}$.

• Slide 19: Bearing grows to $015^{\circ}T$ → alarm; plotted fixes (0700 → 0730) show track bending toward hazard.

• Slide 20: Bearing $020^{\circ}T$ → even closer; imminent danger.

• Alternate case (Slides 21-23) with NLT $057^{\circ}T$: decreasing to $045^{\circ}T$ then $035^{\circ}T$ similarly signals risk.

Memorised Rule-of-Thumb

• Quoted reminder: “Danger bearing is Not More Than $310^{\circ}T$; > $310^{\circ}T$ implies drift left into danger, < $310^{\circ}T$ safe.”

• Encourages helm/engine adjustments as soon as bearing trend violates threshold — do not wait.

Electronic Charts (Generic Overview)

• New technology integrating:

  • Vessel position (GNSS/GPS).

  • Aids-to-navigation, charted objects, hazards.

• Benefits:

  • Real-time situational display.

  • Operations efficiency (automated route planning, ETA, etc.).

• “More than a computer display” → requires mariners to interpret layers, not just view them.

ECS vs ECDIS vs ENC (Terminology)

• ECS (Electronic Chart System): broad term, may not meet IMO performance standards; carriage of paper charts still mandatory if ECS alone.

• ECDIS (Electronic Chart Display & Information System): IMO-compliant, SOLAS Reg. V/19 & V/27 alternative to paper charts when configured with back-up.

• ENC (Electronic Navigational Chart): vector database authenticated by Hydrographic Offices; converted to SENC (System ENC) inside ECDIS.

Raster vs Vector Charts

• Raster: Scanned images of paper charts (pixel-based).

  • Pros: looks identical to paper; minimal training.

  • Cons: no object-level intelligence; file size large; limited zoom.

• Vector (ENC): Layered objects with attributes & interactivity.

  • Pros: selective display, alarms, anti-grounding functions, scale independence.

  • Cons: initial learning curve; potential clutter if poorly filtered.

Electronic Chart Examples (Slides 26-28)

• Screenshots show:

  • Cape Cod Canal & Bay (U.S. coast) with depth contours, light lists, buoy symbols.

  • Poole Harbour / Brownsea Island (U.K.) emphasising yacht moorings, prohibited anchor zones.

  • Seattle / Elliott Bay (U.S.) dense traffic & AIS overlays.

• Pedagogical intent: students practise recognising familiar paper-chart symbology in electronic environment.

ECDIS Architecture & Integrated Bridge

• Shipboard network (Slide 35) interconnects:

  • X-band & S-band radars.

  • DGPS receivers, Gyro, Doppler log, Echo sounder, AIS, NAVTEX, Weather sensors, Auto-Pilot.

  • Conning Display & Chart Radar share data with ECDIS for holistic Bridge decision-making.

• Automatic updates:

  • New ENCs; Notice to Mariners corrections; tidal tables.

  • Continuous track & event recording for post-voyage analysis / legal evidence.

Practical / Ethical / Safety Implications

• Reliance on technology must not erode fundamental chartwork skill (manual bearings, DR, CPA calculations).

• Proper training & certification (STCW, Type-Specific ECDIS) are ethical obligations; mis-use can cause catastrophic accidents.

• Data integrity: only official ENCs guarantee accuracy; un-official charts introduce legal and navigational risk.

Evaluate (Self-Assessment Prompts)

• Explain and differentiate:

  • Danger / Clearing Lines (definition, construction, monitoring procedure).

  • ECDIS (legal status, functions, integration).

  • ECS (non-SOLAS systems, limitations).

  • ENC (vector chart standard, S-57/S-101 formats).

  • Raster vs Vector charts (pros/cons, use cases).

  • Underscale vs Overscale viewing:

  • Underscale = zooming out too far → loss of detail.

  • Overscale = zooming in beyond compilation scale → false sense of accuracy, anti-grounding disabled.

Extend (Applied Task)

• Locate any nautical chart online (e.g., Admiralty, NOAA ENC viewer).

• Plot a danger / clearing bearing using method above:

  1. Choose a hazard (shoal, wreck) & a conspicuous object.

  2. Draw bearing line on protractor tool.

  3. Annotate NMT / NLT limits.

• Document steps with screenshots & explanation for portfolio.