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Browse Nav terms for maritime professionals.

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Advance Transfer Table

A manoeuvring aid providing predicted advance (distance along original track) and transfer (lateral distance) for specific speeds and rudder angles to plan safe turns.

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Air Draft Clearance

The vertical distance from the waterline to the highest point of the vessel, used to determine safe passage under bridges or overhead obstacles.

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Anchor Aweigh Confirmation

The formal notification to the bridge or engine room that the anchor is clear of the seabed and ship is free to maneuver.

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Anchor Heave Rate

The speed at which the anchor cable is hauled in, usually measured in meters per minute, to control anchor recovery.

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Anchor Walkback Control

The controlled paying out of anchor chain in reverse (walkback) under power, used for precise anchor positioning or retrieval.

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Automatic Radar Plotting

The process by which radar targets are tracked and collision risk assessed automatically by ARPA systems, displaying real-time information on target movements and CPA/TCPA.

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Bank Cushion Effect

Hydrodynamic phenomenon where water pressure between a vessel and a nearby bank creates a cushion, pushing the bow away from the bank.

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Bank Suction Effect

Hydrodynamic phenomenon where a vessel navigating close to a bank experiences a suction force pulling the vessel toward the bank due to water velocity difference.

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Bow Tug Position

The assigned and maintained location of a tug at the bow of a vessel to provide pushing, pulling, or steering assistance during berthing, unberthing, or manoeuvring in confined waters.

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Bridge Audio Recording

Continuous audio recording of all conversations and alarms on the bridge as mandated by SOLAS for investigation and safety compliance.

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Bridge Manoeuvring Notebook

A logbook kept on the bridge for recording all manoeuvring orders, engine telegraph movements, helm commands, and critical events during a vessel's navigation and docking.

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Bridge Navigational Watch

A continuous period during which designated officers and crew maintain vigilance and operational control on the bridge to ensure the vessel’s safe navigation.

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Bridge Resource Management

The effective use and coordination of all available bridge resources—personnel, equipment, and information—to ensure safe navigation and vessel operation.

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Channel Design Depth

The minimum depth of a navigational channel as determined and maintained by authorities for safe passage of vessels, referenced to chart datum.

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Check The Swing

Helm or mooring order to observe and, if necessary, limit or arrest the vessel's swinging motion, especially when turning or anchoring.

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Clear Astern Distance

The available unobstructed distance behind the vessel, critical for manoeuvring astern.

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Conning Display Layout

The arrangement of navigation and maneuvering information shown on the conning display for optimal bridge decision-making and situational awareness.

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Course Alteration Point

A precisely charted position where a ship is required to change its course, usually as part of a passage plan.

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Course Made Good

The actual path of a vessel over the ground, as determined by position fixes, regardless of set or drift.

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Cross Track Error

The perpendicular distance between a vessel's actual position and the planned track line, used for navigation accuracy.

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Current Set Drift

The direction (set) and speed (drift) of water current affecting the ship’s course and position.

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Dead Slow Ahead

Engine telegraph order instructing propulsion at the lowest possible speed ahead, used for delicate manoeuvring or congested areas.

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Dead Slow Astern

Engine telegraph order instructing propulsion at the lowest possible speed astern, used for delicate reversing or while manoeuvring in tight spaces.

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Deep Water Route

A route within defined limits in deep water that is charted and designated for the passage of vessels requiring deep draught, providing safe clearance from underwater hazards.

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Dynamic Draught Allowance

An additional draught margin included to account for dynamic effects such as squat, trim, and vessel movement in shallow waters.

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Ease To Five

Helm order instructing the helmsman to reduce rudder angle to five degrees while maintaining course adjustment.

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Electronic Bearing Line

A digital navigational tool on ECDIS or radar for plotting and monitoring bearings to fixed or moving targets, improving situational awareness.

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Electronic Range Line

A digital tool on radar/ECDIS allowing navigators to set and measure a precise distance from own ship to a selected point or target.

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Emergency Steering Position

A dedicated station—usually aft in the steering gear room—used to control the ship’s steering in the event of bridge steering failure.

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Emergency Towing Pennant

A strong wire or rope rigged at bow or stern, readily accessible for emergency towing if the vessel becomes disabled.

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Escort Tug Connection

The established secured line or method by which an escort tug is physically connected to a vessel, typically for controlling or assisting the ship during harbour or restricted water navigation.

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Fairway Centreline Alignment

The practice of steering a vessel so that its longitudinal axis remains aligned with the designated navigational centreline of a fairway, as marked by buoys, lights, or electronic aids.

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Fairway Turning Basin

A designated widened section of a navigational fairway, specifically constructed to allow vessels to safely turn or change direction under pilotage or tug assistance.

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Full Ahead Bell

Engine telegraph order instructing propulsion at full engine speed ahead, typically used in open sea or to quickly gain speed.

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Global Navigation System

A satellite-based navigation system such as GPS, GLONASS, Galileo, or BeiDou, providing worldwide position, navigation, and timing services to vessels.

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Gyro Compass Error

An inaccuracy or malfunction of the ship’s gyro compass, resulting in incorrect heading information displayed to bridge equipment.

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Half Ahead Bell

Engine telegraph order instructing propulsion at half engine speed ahead, used for moderate manoeuvring or departure from berth.

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Harbour Pilot Disembarkation

The controlled process by which the harbour pilot safely leaves the vessel after completing the inbound or outbound passage.

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Harbour Pilot Embarkation

The procedure for safely boarding the harbour pilot at sea or at the entrance of the port using a pilot ladder or launch.

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Harbour Speed Limit

The officially published maximum speed permitted for vessels within a designated harbour or port area, set by local authorities to ensure safety of navigation and infrastructure.

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Hard Port

Helm order instructing the rudder to be put fully to port (left) for maximum turning effect.

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Hard Starboard

Helm order instructing the rudder to be put fully to starboard (right) for maximum turning effect.

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Heading Reference Failure

A malfunction or loss of accuracy in the ship’s heading reference system, such as gyro or magnetic compass, affecting navigation and safe maneuvering.

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Helm Order Acknowledgement

The required verbal response by the helmsman to confirm receipt and understanding of a helm order from the officer of the watch.

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Helm Transfer Procedure

The standardised method for transferring control of the ship’s steering from one helm station or operator to another, ensuring continuous and safe steering.

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Inshore Traffic Zone

A coastal area, adjacent to the landward side of a traffic separation scheme, intended for use by vessels not using the main traffic lanes, such as local or smaller craft.

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Integrity Monitoring Alarm

An alarm signaling a failure or inconsistency detected in the position integrity monitoring system, requiring immediate action.

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Leading Light Alignment

The process of navigating a vessel by visually aligning two or more fixed leading lights (range lights), ensuring the vessel remains on the recommended channel course.

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Leeway Angle Estimate

The calculated or visually assessed angle between a vessel’s heading and actual course over ground, caused by wind or current.

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Let Go All

Final order to release all mooring lines, allowing the vessel to depart from berth.

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Let Go Starboard

Mooring command to release or cast off the starboard (right) mooring line or cable.

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Live Pilot Plug

An active data connection port on the bridge that provides real-time navigational data from the ship's ECDIS or AIS system for the pilot’s portable unit.

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Magnetic Compass Variation

The angular difference between true north and magnetic north, affecting compass readings on board ships.

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Mandatory Reporting Scheme

A regulatory system requiring vessels to provide voyage information at specified locations or intervals, typically enforced by local or international authorities for traffic monitoring and safety.

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Manoeuvring Speed Check

The process of verifying and confirming the vessel’s speed through the water is suitable for safe manoeuvring during berthing, departure, or restricted navigation.

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Master Pilot Exchange

A formal communication process between the ship’s master and the pilot to share essential navigation information, plans, and local hazards before pilotage.

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Meet Her

Helm order given to check the vessel’s swing and prevent further turning, typically after a large rudder movement.

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Midships Rudder

Helm order to bring the rudder to the midships (zero angle) position, aligning with the vessel’s centerline.

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Minimum Breakout Speed

The lowest speed required to break the anchor free from the seabed and commence recovery.

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Minimum Steering Speed

The lowest speed at which the vessel maintains effective steering control, typically specified by the vessel’s maneuvering data.

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Overtaking Prohibition Zone

A defined sector of a channel or waterway where overtaking by vessels is prohibited for safety reasons, often due to restricted width or high traffic density.

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Parallel Index Line

A radar-derived reference line drawn parallel to the vessel's intended track, used to monitor cross-track error by keeping a chosen land echo or seamark at a constant offset.

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Parallel Index Method

A radar navigation technique in which fixed radar echoes are kept on predetermined parallel lines to verify the vessel remains on its planned track without constant position fixing.

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Pilot Boarding Ground

A designated area, marked on charts, where the pilot boards or disembarks from a vessel, usually at port approaches or fairway entrances.

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Pilot Ladder Rigged

A pilot ladder correctly secured and deployed over the ship’s side, ready for safe boarding or disembarkation of the pilot as per SOLAS standards.

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Pilotage Passage Plan

A detailed route plan, prepared jointly by the master and pilot, outlining intended track, waypoints, speed, and manoeuvres for the pilotage operation.

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Position Integrity Monitoring

Continuous verification of the reliability and accuracy of the ship’s position as provided by navigation systems.

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Precautionary Area

A defined area where vessels must navigate with particular caution, often due to traffic convergence, hazards, or complex navigation conditions. Special rules or recommendations may apply.

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Radar Echo Offset

The adjustment of the radar image to compensate for systematic error or offset, ensuring true target positions correspond to their charted locations and improving navigation accuracy.

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Radar Overlay Display

The presentation of radar information directly on the electronic chart display, enabling visual correlation of radar targets with charted features.

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Radar Plotting Manual

A publication or onboard manual containing standardized instructions, techniques, and worksheets for manually plotting radar targets to assess collision risk and avoidance actions.

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Range Light Alignment

The navigation technique of steering a vessel so that two range lights, one behind the other, appear vertically aligned, indicating the vessel is on the safe channel axis.

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Rate Of Turn

The speed at which a vessel changes its heading, typically measured in degrees per minute and displayed on the bridge instrument panel.

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Recommended Traffic Lane

A charted route within a traffic separation scheme or recommended track designed for the safe passage of vessels, but not compulsory. Usage reduces collision risk.

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Safe Water Mark

IALA buoyage mark indicating there is navigable water all around the mark.

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Satellite Position Fix

A position determined using satellite navigation signals, typically from systems like GPS or GLONASS, used for precise ship positioning.

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Single Up Lines

Order to reduce the number of mooring lines on each bollard to one, preparing the vessel for departure.

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Slow Ahead Bell

The engine telegraph order for slow speed ahead, typically used during precise manoeuvring, docking, or when entering confined waters.

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Squat Effect Allowance

The additional draught margin applied to account for the increased draught of a vessel due to the squat effect in shallow water.

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Standby Main Engines

Order for main engines to be ready for immediate use, typically before departure, arrival, or manoeuvring.

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Steering Gear Changeover

The act of switching from one steering gear system or power unit to another, often for redundancy or in case of equipment failure.

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Stern Tug Position

The designated location of a tug at the stern of a vessel, used to provide pulling or braking force during manoeuvring, berthing, or unberthing operations.

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Stop Main Engines

Engine telegraph order to cease all propulsion; used when vessel is to remain stationary or fully secured at berth.

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Terrestrial Position Fix

A position established by bearings or distances to known land features or aids to navigation, not using satellites.

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Tidal Window Calculation

The process of determining the optimal period based on tidal height during which a vessel can safely transit shallow waters or cross a bar.

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Track Made Good

The actual path a vessel follows over the ground, as recorded by position fixes, often used interchangeably with course made good.

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Traffic Separation Scheme

An internationally recognized routing measure that separates opposing streams of vessel traffic by defined lanes and rules to reduce collision risk in busy or restricted waters.

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Transverse Thrust Correction

The adjustment applied to helm or engine orders to compensate for the sideways force exerted by a propeller, especially during astern or ahead movements.

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Tug Allocation Plan

A detailed arrangement indicating the number, type, and position of tugs assigned to assist a vessel during berthing, unberthing, or transit in restricted waters.

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Turning Circle Diameter

The distance perpendicular to the original track between tangents of the vessel’s path when executing a steady-turn at a given rudder angle and speed, usually expressed in ship lengths or cables.

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Under-Bridge Clearance

The vertical distance between the lowest part of the bridge span and the highest point of the vessel, ensuring safe passage.

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Underkeel Clearance

Vertical distance between the lowest point of a vessel’s keel and the seabed referenced to chart datum; the key safety margin preventing grounding.

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Vector Chart Display

An electronic navigational chart presented in vector format, enabling interactive layers and detailed, scalable map features for navigation and route planning.

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VTS Reporting Point

A specifically designated geographical position where a vessel is required to contact and report to the Vessel Traffic Service (VTS) with position, status, and intentions.

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Waypoint Sequencing Alarm

An alarm on navigation systems indicating failure to automatically advance to the next waypoint as programmed in the voyage plan.

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Wheel Over Alarm

An electronic or mechanical alarm that notifies the bridge team when it is time to initiate the wheel-over manoeuvre, usually at a pre-set waypoint or heading.

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Wheel Over Line

A track line shown on chart or radar which, when crossed, indicates the precise moment to start the wheel-over so that the intended new course is met accurately.

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Wheel Over Point

The charted position at which the rudder is first applied to initiate a planned course alteration so that the vessel follows the intended turning track.

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Windage Area Effect

The influence of the ship’s exposed surface area above the waterline, causing increased drift or leeway under wind pressure.

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