2.1 Bridge Layout, Compass, Helmsman Duties & Steering Orders

Bridge Layout, Compass, Helmsman Duties & Steering Orders

Safe navigation demands seamless coordination between the conning officer and the deck ratings on watch. The navigation bridge serves as the command center of the ship, housing the sensory, steering, and communication interfaces necessary to traverse open oceans, congested sealanes, and narrow pilotage waters. For a General Purpose (GP) rating, mastering the bridge equipment layout, understanding compass operation, executing precise helmsman duties, and adhering strictly to Standard Marine Communication Phrases (SMCP) are foundational professional competencies.

---

1. Bridge Layout & Key Navigational Equipment

Under SOLAS V/22, ships at least 55 m in length overall constructed on or after 1 July 1998 normally require a horizontal view of at least 225° from the conning position, extending to 22.5° abaft each beam. From the main steering position, the view must extend from ahead to at least 60° on each side. Modern wheelhouses group equipment into workstations for clear access and observation.

                               FORWARD (BOW)
      +-------------------------------------------------------------+
      |                         BRIDGE WINDOWS                      |
      |                                                             |
      |   [RADAR / ARPA]      [STEERING CONSOLE]     [RADAR / ARPA] |
      |      (X-Band)            Helm / Wheel           (S-Band)    |
      |                       Rudder Angle Ind.                     |
      |                                                             |
      |   [ECDIS CONSOLE]     [ENGINE TELEGRAPH]     [ECHO SOUNDER] |
      |   Primary Nav Display   Propulsion Control     & SPEED LOG  |
      |                                                             |
PORT  |   [VHF RADIO STN]                            [INTERNAL COMM]| STARBOARD
WING  |    Ch 16 / 13 / 6                             Talkback / PA | WING
      |                                                             |
      |   [CHART TABLE]                              [GMDSS CONSOLE]|
      |   Passage Plan / Pubs                        Distress Radio |
      +-------------------------------------------------------------+
                                AFT (STERN)

Primary Bridge Workstations and Equipment

1. Steering Console (Helm Station): Located on the bridge centerline to ensure the helmsman has an unobstructed view dead ahead. Houses the manual steering wheel, autopilot control unit, steering mode selector switch (Hand / Auto / NFU), gyro repeater, and the overhead Rudder Angle Indicator (RAI).
2. Engine Order Telegraph (EOT): Positioned adjacent to the conning position. Transmits propulsion speed orders from the bridge to the engine control room (or provides direct bridge throttle control in bridge-control mode). Standard orders include: Stand By Engine, Dead Slow Ahead, Slow Ahead, Half Ahead, Full Ahead, Stop Engine, Dead Slow Astern, Slow Astern, Half Astern, Full Astern, and Finished With Engines (FWE).
3. Radar and ARPA (Automatic Radar Plotting Aid): Vessels operate dual marine radar bands:
   • X-Band ($3\text{ cm}$ / $9\text{ GHz}$): High-resolution discrimination of small targets, coastlines, navigation buoys, and search-and-rescue transponders (SART).
   • S-Band ($10\text{ cm}$ / $3\text{ GHz}$): Longer wavelength offering superior penetration through heavy rain, snow, sea clutter, and atmospheric squalls.
4. ECDIS (Electronic Chart Display and Information System): Real-time electronic navigation workstation displaying official Electronic Navigational Charts (ENCs), continuous GPS/GNSS vessel positioning, planned route tracks, safety depth contours, and integrated radar/AIS target overlays.
5. Echo Sounder: Acoustic depth sounder measuring water depth below the hull. It can display depth below transducer, depth below keel (DBK), or depth below sea surface waterline. Equipped with visual digital depth readouts, continuous graphical history recording, and adjustable shallow-water depth alarms.
6. Speed Log: Measures vessel speed through the water (Doppler or electromagnetic sensor) or speed over the ground (dual-axis Doppler log tracking seabed acoustic reflections).
7. Magnetic Compass Binnacle: Positioned on the monkey island (compass deck) directly above the bridge centerline, viewed from the steering console via an optical periscope reflector tube, or monitored through an electronic fluxgate sensor transmitting to a digital repeater.
8. Gyro Repeaters: Electrically driven repeaters positioned at the steering stand and on the port and starboard bridge wings. Bridge wing repeaters are fitted with rotatable azimuth circles (pelorus) for taking visual bearings of terrestrial objects, celestial bodies, and incoming vessels.
9. VHF Radiotelephone: Critical bridge-to-bridge and bridge-to-shore maritime radio communications:
   • Channel 16 ($156.8\text{ MHz}$): International distress, urgency, safety calling, and initial hailing.
   • Channel 13 ($156.65\text{ MHz}$): Bridge-to-bridge navigational safety communications (inter-ship collision avoidance).
   • Channel 6 ($156.3\text{ MHz}$): Inter-ship search and rescue (SAR) coordination.

---

Chart Position, Distance and Scale

Latitude measures position north or south of the Equator, from 0° to 90°; longitude measures east or west of the Greenwich prime meridian, from 0° to 180°. Degrees divide into 60 minutes. On a Mercator chart, parallels of latitude and meridians of longitude form a rectangular grid.

To plot 19°00′N, 072°45′E, find 19°00′ on the side latitude scale and 072°45′ on the top or bottom longitude scale. Project each into the chart with suitable plotting instruments; their intersection is the position. Mark the time and the position’s source or method as instructed by the OOW. Check both hemispheres and all digits before using a reported position.

Measure distance with dividers and read their span against the latitude scale beside the area concerned: one minute of latitude represents one nautical mile. Use the latitude scale for Mercator distance, rather than the longitude scale. A knot is one nautical mile per hour; one international nautical mile is 1852 m.

Worked check: Positions 19°00′N and 19°06′N on the same meridian are 6 nautical miles apart. At 6 knots, covering that distance takes 6 ÷ 6 = 1 hour.

A large-scale harbour chart shows a smaller area in greater detail. At 1:20,000, 1 cm represents 200 m; at 1:200,000 it represents 2 km. Use the appropriate corrected chart and its symbols, notes and datum. Practise plotting and measuring under supervision; a rating reports information and follows the OOW’s instructions.

2. Magnetic Compass vs. Gyro Compass

SOLAS V/19 requires a properly adjusted magnetic compass, or approved equivalent, for heading independently of electrical power. Ships of 500 GT and above additionally require a gyro compass or approved other non-magnetic heading means, with the prescribed heading outputs and repeaters.

The Magnetic Compass

The magnetic compass is an autonomous, self-contained instrument that aligns freely with Earth's geomagnetic field. It requires no electrical power, making it the ultimate failsafe navigation reference during total blackout or electrical plant failure.

• Construction: The magnetic compass card is graduated in degrees from $000^\circ$ to $360^\circ$. The card floats inside a sealed brass bowl filled with a damping liquid—a mixture of pure ethyl alcohol and distilled water (freezing point below $-30^\circ\text{C}$, specific gravity ~0.93) to minimize friction on the iridium-tipped pivot and damp oscillations caused by ship rolling. The bowl is suspended in two concentric brass rings (gimbals) ensuring the card remains perfectly horizontal regardless of vessel motion. A fine vertical reference mark etched inside the bowl, the lubber line, indicates the vessel's fore-and-aft centerline heading.
• Variation (Var): The angular difference between the True Geographic Meridian (True North) and the Magnetic Meridian (Magnetic North). Variation is caused by the physical displacement of Earth's magnetic poles relative to its rotational axis. It changes with geographical location and drifts slowly over time; the local variation and annual rate of change are printed on the nautical chart compass rose.
• Deviation (Dev): The angular error between the Magnetic Meridian and the Compass Needle Axis (Compass North). Deviation is caused by the ship's own magnetic field, composed of permanent magnetism hammered into the hull during shipyard construction and temporary induced magnetism acquired from Earth's field, steel cargo, and heavy machinery.
• The Binnacle & Correction Components: The non-magnetic pedestal housing the compass bowl contains specialized correctors adjusted by a certified compass adjuster:
  • Soft Iron Spheres (Kelvin's Balls): Large hollow spheres of annealed soft iron mounted on port and starboard brackets athwartships. They correct for quadrantal deviation induced by horizontal transverse and longitudinal ship steel.
  • Flinders Bar: A vertical cylinder of soft iron housed in a brass case mounted forward or abaft the binnacle. It corrects for semicircular deviation induced by vertical soft iron structures.
  • Fore-and-Aft & Athwartship Corrector Magnets: Permanent bar magnets (B and C correctors) placed in horizontal internal trays beneath the compass bowl to neutralize the ship's permanent magnetic poles.
  • Heeling Error Magnet: A permanent magnet suspended vertically inside a bucket on a brass chain directly beneath the center of the compass card to counteract magnetic vertical pull when the vessel rolls or lists.

                  MAGNETIC COMPASS TO TRUE HEADING FLOW
   Compass Course (C)  -->  [ Apply Deviation ]  -->  Magnetic Course (M)
   Magnetic Course (M) -->  [ Apply Variation ]  -->  True Course (T)

   Rule: East is Least (Subtract when going True -> Compass)
         West is Best  (Add when going True -> Compass)
   Rule: Add East (+), Subtract West (-) when going Compass -> True

$\text{Compass Heading} \pm \text{Deviation} = \text{Magnetic Heading}$ $\text{Magnetic Heading} \pm \text{Variation} = \text{True Heading}$

The Gyro Compass

The gyro compass operates on the principle of a heavy, electrically driven rotor spinning at high speed ($8{,}000$ to $24{,}000\text{ rpm}$) mounted in gimbals with three degrees of freedom. Governed by the fundamental laws of gyroscopic inertia (rigidity in space) and precession, combined with Earth's rotation and gravity control, the spin axis settles continuously along the local geographic meridian, pointing directly to True North.

• Advantages: Indicates True North directly without requiring variation or deviation corrections; completely unaffected by ship's steel, hull magnetism, or metallic cargo; supplies electronic digital and analog heading signals directly to the autopilot, radar displays, ECDIS, and directional antennas.
• Limitations: Dependent on an uninterrupted electrical power supply (backed up by an emergency battery/UPS); requires 2 to 4 hours to spin up and settle if completely shut down; subject to small dynamic errors (latitude error, course and speed steaming error) which are automatically computed and corrected by inputting speed and latitude data.

---

3. Helmsman Responsibilities & Steering Gear Operations

The helmsman is entrusted with the direct directional control of the vessel. The lives of the crew, the safety of the ship, and the protection of the marine environment depend on the helmsman's unwavering concentration and precise adherence to steering orders.

Core Responsibilities of the Helmsman

1. Maintain Ordered Course: Steer the vessel precisely on the conning officer's ordered compass heading, keeping the yaw (swing) to an absolute minimum.
2. Continuous Monitoring: Frequently cross-check the steering gyro repeater against the magnetic compass heading and monitor the overhead Rudder Angle Indicator (RAI) to verify that physical rudder response corresponds to wheel demand.
3. Early Anomaly Detection: Instantly report any abnormal resistance, sluggish rudder movement, excessive yawing, or failure of the rudder to return to centerline.
4. Uncompromised Focus: Never abandon the steering wheel until properly relieved by a qualified rating in the presence and with the explicit permission of the Officer of the Watch (OOW).

Steering Modes & Manual Steering Mandate

Modern steering consoles offer three distinct steering modes:

• Auto (Autopilot): An electronic PID (Proportional-Integral-Derivative) control system that senses heading deviations and applies calculated rudder angles automatically. Ideal for open-ocean transit under stable weather conditions.
• Hand (Manual Steering): Direct human control of the wheel. The steering gear telemotor translates wheel input directly into proportional hydraulic rudder movement.
• Non-Follow-Up (NFU): Emergency or secondary steering mode using a spring-loaded toggle switch or tiller lever. Deflecting the lever energizes the hydraulic solenoids directly; the rudder moves continuously as long as the lever is held, and stops wherever it is when released. It does not return to midships automatically.

Steering Gear Changeover Procedures

Switching from Autopilot to Hand Steering (Auto to Hand):

1. Inform the OOW of the intention to switch over and obtain verbal confirmation.
2. Note the ship's current gyro heading and confirm the vessel is steady on course.
3. Check the physical rudder angle indicator to confirm rudder position.
4. Rotate the steering mode selector switch firmly from "AUTO" to "HAND".
5. Take physical grip of the helm wheel and apply a slight trial helm movement (e.g., $2^\circ$--$3^\circ$ port and starboard) while observing the rudder angle indicator to verify positive hydraulic response.
6. Steady the vessel on the ordered course.
7. Report clearly to the conning officer: "Steering manual, vessel steady on course zero-eight-five, sir."

Switching from Hand Steering to Autopilot (Hand to Auto):

1. Ensure the vessel is steady on the ordered course by manual steering.
2. Bring the rudder to zero degrees ($0^\circ$ / midships), confirmed on the rudder angle indicator.
3. Adjust the autopilot heading selector bug/dial to match the vessel's current gyro heading exactly.
4. Rotate the mode selector switch from "HAND" to "AUTO".
5. Stand by the wheel for several minutes, closely observing the rudder angle indicator and gyro repeater to confirm that the autopilot captures and maintains the heading without oscillation or hunting.
6. Report to the OOW: "Vessel switched to autopilot, steady on course zero-eight-five, sir."

---

4. Standard Helm Orders (IMO SMCP)

To prevent catastrophic navigational misunderstandings, the International Maritime Organization (IMO) established strict Standard Marine Communication Phrases (SMCP) for steering commands. Every helm command requires a disciplined, four-step closed-loop communication cycle:

   1. Conning Officer gives order  -->  "Starboard ten!"
   2. Helmsman repeats verbatim    -->  "Starboard ten, sir."
   3. Helmsman executes helm       -->  (Applies 10 deg starboard rudder)
   4. Helmsman reports completion  -->  "Rudder is starboard ten, sir."
   5. Conning Officer acknowledges -->  "Very well."

Essential IMO Helm Orders and Meaning