Principles of Under Keel Clearance and Earth's Magnetism

This set of flashcards covers key concepts related to Under Keel Clearance, navigation safety, and the fundamentals of Earth's magnetism as presented in the lecture notes.

Under Keel Clearance (UKC)

The vertical distance between the lowest point of a ship's keel and the seabed.

Ship's Draft

The vertical distance between the waterline and the lowest point of the ship's hull, typically the keel.

Depth of Water

The total vertical distance from the sea surface to the seabed at a ship’s position.

Squat Effect

The phenomenon where a ship sinks lower in the water, reducing the under keel clearance, especially at higher speeds in shallow waters.

Charted Depth

The depth of water indicated on nautical charts, usually at mean low tide.

Tides

The state of the tide that affects water depth; high tide provides more clearance, while low tide reduces depth.

Safety Management System (SMS)

A formal system that ensures safety in maritime operations, which may include policies on Under Keel Clearance.

Dynamic Under Keel Clearance

A consideration of the changing depth of water under a ship based on operational conditions.

Variation

The angular difference between true north and magnetic north affecting navigation accuracy.

Deviation

Deflection of the compass needle caused by magnetic properties of the ship, which can vary with heading.

Magnetic North vs. True North

Magnetic north is the direction a compass points, while true north is the geographic North Pole.

Angle of Magnetic Dip

The vertical angle between the horizontal and a line of magnetic force, indicating the strength and direction of magnetic fields.

Isogonic Line

Lines connecting points of equal magnetic variation on a map.

Soft Iron vs. Hard Iron

Soft iron can be easily magnetized and demagnetized, while hard iron retains a significant amount of magnetism once magnetized.

Compensating the Compass

The process of correcting the compass reading to account for deviation and variation, ensuring accurate navigation.

Estimation of Squat

Factors influencing the squat effect include speed, water depth, and the vessel's shape.

Zone of Confidence (CATZOC)

A classification indicating the level of confidence in the accuracy of the depth information in a particular area.

Air Draft

The vertical distance from the waterline to the highest point of a vessel, critical for passing under bridges or overhead obstacles.

Lubber Line

A mark inside a compass bowl indicating the ship's fore-and-aft line, used to read the ship's head.

Gyro Compass

A type of non-magnetic compass that finds true north based on the properties of a rapidly spinning rotor, unaffected by magnetic fields.

Course Over Ground (COG)

The actual path of a vessel over the seabed, influenced by current and wind.

Speed Over Ground (SOG)

The actual speed of a vessel relative to the seabed, reflecting movement after accounting for currents.

Electronic Chart Display and Information System (ECDIS)

A navigation information system that displays electronic nautical charts and integrates position information, allowing for route planning and monitoring.

Automatic Identification System (AIS)

A system used by vessels and vessel traffic services to identify and locate ships by electronically exchanging data with other nearby ships and land stations.

Global Positioning System (GPS)

A satellite-based navigation system that provides location, velocity, and time synchronization.

Radar (Radio Detection and Ranging)

A navigation aid that uses radio waves to determine the range, angle, or velocity of objects.

Automatic Radar Plotting Aid (ARPA)

A radar feature that automatically tracks targets, calculates their course and speed, and predicts collision risks.

Bridge Watchkeeping

The process of maintaining a proper lookout, navigating, and monitoring the vessel's safety and operational status from the ship's bridge.

Passage Plan

A comprehensive plan detailing a ship's voyage from berth to berth, including routes, navigational hazards, weather, and emergency procedures.

IALA Buoyage System

The international maritime buoyage system (either Region A or B) used worldwide to mark navigable channels and hazards.

COLREGs (Collision Regulations)

International Regulations for Preventing Collisions at Sea, providing rules for vessel lights, shapes, sound signals, and steering/sailing to avoid collisions.

Steering Gear

The equipment used to control the rudder and thus the direction of the ship.

Propeller

A device with a rotating hub and radiating blades that propels a vessel through water.

Fathom

A unit of depth equal to 6 feet or 1.8288 meters, commonly used in nautical charts.

Shallow Water Effect

The phenomenon where a ship behaves differently in shallow water compared to deep water, including increased resistance and squat.

Dead Reckoning (DR)

A method of navigation by calculating current position using a previously determined position, course, and speed.

Estimated Position (EP)

A position determined by applying an estimate of currents and winds to a dead reckoning position.

Fix

An accurate position determined from celestial observations, electronic navigation systems (like GPS), or terrestrial observations.

Bearing

The horizontal direction of an object from the observer, usually expressed as an angle from north.

Range

The distance from the observer to an object.

EPIRB (Emergency Position Indicating Radio Beacon)

A distress beacon used to alert rescue services in an emergency.

SART (Search and Rescue Transponder)

A device that responds to radar signals, aiding in locating life rafts or distressed vessels.

GMDSS (Global Maritime Distress and Safety System)

An international system using advanced communication technology to ensure rapid relay of distress alerts.

VHF Radio (Very High Frequency Radio)

A short-range radio communication system used for ship-to-ship and ship-to-shore communication.

Magnetic Compass Rose

A circle printed on nautical charts from which bearings can be taken.

Rhumb Line (Loxodrome)

A line on the surface of the earth that cuts all meridians at the same angle, used for plotting courses on a Mercator chart.

Great Circle

The shortest distance between two points on the surface of a sphere, used for long-distance oceanic voyages.

Set and Drift

Set refers to the direction of the current, and drift refers to its speed.

Leeway

The sideways movement of a vessel caused by wind.

Anchoring

The process of securing a vessel to the seabed using an anchor and chain.

Pilotage

The act of navigating a vessel in restricted waters, typically with the assistance of a local pilot.

Berth

A designated space where a ship can dock or anchor.

Fairway

A navigable channel in a river, harbor, or strait.

Aids to Navigation (AtoN)

Devices or systems external to vessels, such as lighthouses, buoys, and beacons, designed to assist mariners in navigation.

Lights Characteristics

The specific pattern of light (e.g., flashing, fixed, occulting) emitted by lighthouses and buoys for identification.

Sound Signals

Audible signals used by vessels to indicate their presence or maneuvering intentions, especially in restricted visibility.

Ballast Water Management

The process of managing ballast water to prevent the transfer of harmful aquatic organisms and pathogens.

MARPOL (International Convention for the Prevention of Pollution from Ships)

The main international convention covering prevention of pollution of the marine environment by ships from operational or accidental causes.

SOLAS (International Convention for the Safety of Life at Sea)

An international maritime treaty establishing minimum safety standards in the construction, equipment, and operation of merchant ships.

ISM Code (International Safety Management Code)

An international standard for the safe management and operation of ships and for pollution prevention.

Watchkeeping Officer

A qualified officer responsible for maintaining a safe navigational watch on the bridge.

Lookout

A person assigned to keep a continuous watch for navigational hazards, other vessels, and persons in the water.

Port State Control (PSC)

The inspection of foreign ships in national ports to verify that the condition of the ship and its equipment complies with international regulations.

Flag State Control

The authority that a state exercises over a vessel registered under its flag, ensuring compliance with international maritime law.

Gross Tonnage (GT)

A non-linear measure of a ship's overall internal volume, used to determine regulations, manning, and safety requirements.

Net Tonnage (NT)

A measure of the ship's actual cargo-carrying capacity, used for calculating port dues and other fees.

Load Lines (Plimsoll Lines)

Marks on a ship's hull indicating the maximum depth to which the vessel may be safely loaded in various sea areas and seasons.

Draught Marks

Numerals painted on the ship's bow, stern, and midships indicating the depth of the hull below the waterline.

Freeboard

The distance from the waterline to the main deck, indicating the reserve buoyancy of the vessel.

Heeling

The temporary inclination of a ship due to wind, waves, or turning maneuvers, from which it normally recovers.