HKIE Professional Assessment - Marine & Naval Architecture Discipline key terms

The vertical distance between a vessel's centre of gravity and its transverse metacentre. A positive value indicates an initially stable ship; it governs the stiffness of roll and is fundamental to the intact stability assessment.

The horizontal offset between the centre of gravity and the line of buoyancy force at a given heel angle. Multiplying GZ by displacement gives the righting moment, and the plotted GZ curve defines stability range and angle of vanishing stability.

The virtual rise of a ship's centre of gravity caused by liquid shifting in a partly filled tank as the vessel heels. It reduces effective metacentric height and is minimised by subdivision of tanks or by pressing tanks full.

A state in which a ship with negative initial metacentric height rests at a steady heel to either side, where the GZ curve crosses zero with positive slope. Corrective action is to lower the centre of gravity, not to counter-flood high side tanks.

Assessment of a vessel's ability to survive flooding of specified compartments, showing that residual freeboard, righting energy and margin line immersion remain acceptable. It underpins subdivision requirements and probabilistic survivability standards for passenger and cargo ships.

A line drawn at least 76 mm below the upper surface of the bulkhead deck at side, used in damage stability calculations as the limit below which the vessel must remain after assumed flooding. It appears in SOLAS subdivision and damage stability criteria.

The maximum length used in subdivision and damage stability calculations, measured between the forward and aft extremities of the load waterline at the deepest subdivision draught. It sets the reference for permissible compartment lengths and floodable lengths.

The ratio of a hull's displaced volume to the volume of a rectangular block of its length, breadth and draught. It expresses hull fullness and correlates strongly with resistance characteristics and required propulsive power.

The ratio of displaced volume to the volume of a prism with the same midship section area and length. It indicates how volume is distributed along the hull and is closely linked to wave-making behaviour.

A dimensionless speed parameter equal to speed divided by the square root of length times gravitational acceleration. It governs wave-making resistance and dynamic similarity, so model tests are run at matching Froude number.

The component of ship resistance caused by energy radiated in the wave system the hull generates. It rises sharply near the hull-speed limit and is the dominant reason for the practical speed ceiling of displacement vessels.

A multiplier applied to frictional resistance to account for pressure and viscous effects of hull form beyond a flat plate. It is derived from model tests or empirical methods and used in resistance prediction.

A protruding bulb at the forward underwater end of a hull that generates its own wave system to partially cancel the bow wave. It reduces wave-making resistance over a designed speed range but can increase resistance outside that range.

Experimental towing of a geometrically scaled model in a towing tank to measure resistance, propulsion or seakeeping characteristics, with results extrapolated to full scale using Froude and Reynolds scaling laws.

The fractional reduction in water speed at the propeller compared with the ship's speed, arising from the hull's boundary layer and flow field. It is used to relate ship speed to advance speed through the propeller.

The fractional reduction in effective thrust caused by the propeller accelerating water that lowers pressure over the aft hull, adding resistance. It links measured propeller thrust to the effective thrust pushing the ship.

The ratio of useful power delivered to the ship (resistance times speed) to the power absorbed by the propeller. It combines hull efficiency, open-water propeller efficiency and relative rotative efficiency.

Formation and collapse of vapour bubbles in low-pressure regions of a propeller or pump, causing noise, erosion, vibration and loss of thrust. Avoidance requires limiting blade loading and ensuring adequate immersion.

The arrangement of hull form and rudder support around the propeller that determines water inflow quality and clearances. Adequate aperture reduces vibration, cavitation risk and uneven wake.

A resonant rolling phenomenon in following or quartering seas caused by periodic variation of waterplane area as waves pass the hull, producing large roll angles at low encounter frequency. It is a recognised stability hazard for container ships.

The ability of a hull girder to withstand bending moments and shear forces from cargo distribution and from wave-induced loading. It is checked against section modulus and permissible stress criteria in classification rules.

A geometric property of a hull cross-section equal to second moment of area divided by distance to the extreme fibre. It converts bending moment into extreme stress and is the primary measure of girder bending capacity.

The ship's hull treated as a box beam resisting longitudinal bending, comprising deck, bottom, side shell and longitudinal stiffening. Its effectiveness depends on continuity of structure and avoidance of stress concentrations.

Progressive crack initiation and growth under repeated cyclic stress, such as wave loading on welded details. It is assessed using S-N curves and cumulative damage rules, and controlled by detail design and weld quality.

An extra thickness added to structural members to compensate for expected wastage over the ship's life. It is specified in classification rules and verified by periodical thickness gauging during surveys.

Loss of stability of a slender structural member under compressive load, causing sudden lateral deflection at a load below the material yield stress. It governs stiffener and plating design for deck and bottom structures.

Inspection methods such as ultrasonic, radiographic, magnetic particle and dye penetrant testing that reveal internal or surface defects without damaging the structure. NDT is applied to critical welds and used to verify repair quality.

Fabrication of hull sections as blocks in a workshop, then joining them into larger units and erecting them in the dock. It improves access, dimensional control and productivity compared with piece-by-piece construction.

Installation of piping, cabling, ducting and equipment into hull blocks before erection, so work is done at floor level with better access. It reduces dock time and overall build cost.

Unintended deformation of fabricated structure caused by localised heating, shrinkage and residual stress during welding. It is controlled by welding sequence, restraint, heat input and fairing, and affects dimensional accuracy and fit-up.

An independent organisation that develops and administers technical rules for hull, machinery and equipment, issuing class certificates and conducting surveys on behalf of owners and flag states. Class is evidence of structural and mechanical fitness, not of statutory compliance itself.

The flag state certifies a ship against international conventions it has ratified, while port state control inspects foreign ships in port for compliance and may detain deficient vessels. Both mechanisms enforce safety and pollution standards.

A certificate issued under an international convention, such as safety construction, safety equipment, load line or MARPOL certificates, confirming compliance. It is issued by or on behalf of the flag administration, often delegated to a recognised organisation.

A structured inspection of hull structure and equipment to establish actual condition, typically involving close-up survey, thickness measurement and assessment of corrosion and cracks. Findings drive repairs, class recommendations and continued certification.

The International Safety Management Code requires companies to operate a documented safety management system covering policies, responsibilities, procedures and emergency preparedness, verified by audit. It applies to ships and their shore management.

A structured risk-based methodology identifying hazards, assessing risk, evaluating risk control options and comparing costs and benefits. It is used within IMO rule-making to support decisions on safety measures.

The requirement that risks be reduced to a level that is as low as reasonably practicable, weighing further risk reduction against cost, time and difficulty. It underpins safety case regimes and risk acceptance decisions.

Measures to prevent transfer of harmful aquatic organisms between regions, principally by treatment to an approved standard before discharge. Compliance involves an approved management plan, records and surveys.

The air pollution prevention annex of MARPOL, covering sulphur oxide and nitrogen oxide limits, ozone-depleting substances, volatile organic compounds and energy efficiency requirements. It drives fuel selection, scrubber or alternative fuel choices and EEDI/EEXI compliance.

The mass of fuel a prime mover consumes per unit of shaft work or electrical output, usually expressed in grams per kilowatt-hour. It is a key indicator of plant efficiency and directly affects operating cost and emissions.

The system transmitting torque from the propulsion engine to the propeller, comprising intermediate shafts, bearings, stern tube and propeller shaft. Alignment, bearing loads and sealing are critical to reliability and vibration control.

Periodic withdrawal or in-situ inspection of the propeller shaft and stern tube bearings to detect wear, corrosion, cracks and seal condition. It is a class requirement at defined intervals and may be extended under approved conditions.

An industrial digital controller executing a stored program to read sensors and drive actuators in machinery systems. It provides alarm handling, interlocks, sequencing and remote monitoring on board.

A class notation permitting periodically unattended operation of the engine room, requiring alarms, automatic shutdowns, fire detection and safety systems proven by survey. It depends on reliable automation and remote monitoring.

Arrangement of duplicated equipment or components so a single failure does not prevent essential functions, and design so failures result in a safe state. It is applied to steering, propulsion, power supply and safety systems.

The standards of integrity, competence, public safety, confidentiality and fair dealing expected of a professional engineer, including obligations to report unsafe practice and to avoid conflicts of interest. Breach can lead to disciplinary action.

The professional obligation to escalate serious safety or environmental concerns through appropriate channels, including outside the employer when internal routes fail, placing public welfare above commercial or personal interest.

Structured ongoing learning and reflective practice required to maintain and enhance technical competence and professional judgement throughout a career, typically recorded and reported to the professional institution.