Ship Science and Engineering

Naval Architecture glossary

The parent engineering discipline of the ship: hull geometry and hydrostatics, resistance and powering (the Holtrop-Mennen method, the Admiralty coefficient), propeller hydrodynamics and cavitation, seakeeping, maneuvering, and the design spiral. Includes structural design under the IACS Common Structural Rules, hull-girder strength and FEA, intact and damage stability under the IS Code and the Second Generation Criteria, and freeboard under the Load Line Convention.

311 defined terms.

Showing 250 on this page (page 1 of 2).

A

Added mass: Apparent increase in vessel mass due to fluid acceleration around the hull during motion.
Added resistance in waves: Mean increase in calm-water resistance caused by wave-induced motions and reflections.
Admiralty coefficient: Empirical powering relation P = (D^(2/3) V^3)/C used for first-cut shaft-power estimates.
Aframe (model basin): Carriage gantry supporting dynamometers above the towing tank.
Afterbody: Portion of the hull aft of midships, governing wake and propeller inflow.
Air draft: Vertical distance from waterline to highest fixed point of the ship.
Akima spline: Smooth interpolation used for fairing hull offsets.
Amidships: Longitudinal midpoint between the forward and aft perpendiculars.
Angle of loll: Static heel of a vessel with negative initial GM that has rolled to a position of positive righting arm.
Angle of vanishing stability (AVS): Heel angle at which the righting arm GZ returns to zero on the static stability curve.
Appendage resistance: Drag contribution of rudders, bilge keels, shafts, brackets, bossings, and stabilizer fins.
Aquaplane (rudder): Horizontal lifting surface fitted on a rudder to reduce induced drag.
Areal density (plating): Mass per unit area used in weight estimates.
Aspect ratio (foil): Ratio of span squared to planform area for rudders, foils, and fins.
Asymmetric stern: Hull form with port/starboard asymmetry tuned for propeller wake.
Athwartships: Direction transverse to the ship's centerline.
Atwood's formula: Geometric formulation of the righting arm via wedge transfer of buoyancy.
Autopilot interaction (maneuvering): Coupling of course-keeping controller with hull dynamics in standard maneuvers.
Axe bow: Vertical, deep-forefoot bow form used on offshore supply vessels.
Axial inflow factor: Ratio relating mean axial velocity at propeller disk to ship speed.

B

Bale capacity: Cargo volume measured to the inside of frames and below beams.
Ballast condition: Loading condition with no cargo, only ballast water and consumables.
Bare hull resistance: Calm-water resistance excluding appendages.
Beam (B): Maximum breadth of the hull.
Beam-to-draft ratio (B/T): Form parameter influencing stability and resistance.
Bending moment (longitudinal): Internal moment along the ship girder from buoyancy/weight imbalance.
Bentley MAXSURF: Commercial hull design and hydrostatics suite.
Bernoulli equation: Energy relation along a streamline used in potential flow analysis.
Bilge keel: Longitudinal fin on the turn of bilge to damp roll motion.
Bilge radius: Curvature joining bottom and side shell at the turn of bilge.
Block coefficient (CB): Ratio of displaced volume to L*B*T.
Bonjean curves: Sectional area versus draft used in hydrostatic calculations.
Bossing: Faired housing around shaft exit on twin-screw vessels.
Boundary element method (BEM): Panel method solving Laplace's equation for potential flow.
Boundary layer: Thin viscous region adjacent to the hull.
Bow flare: Outward curvature of the forward sections above the waterline.
Bow thruster: Transverse-tunnel thruster forward for low-speed maneuvering.
Breadth at the design waterline (BWL): Beam at design draft.
Brennan resistance components: Decomposition into frictional, residual, and air resistance.
Broaching-to: Loss of course in following or stern-quartering seas.
Bulb keel: Ballast bulb at the keel of a sailing yacht.
Bulbous bow: Forward protrusion at the stem to reduce wave-making resistance.
Bunkers (weight item): Mass of fuels carried, an input to the deadweight calculation.

C

Cargo deadweight (DWCC): Carrying capacity less fuels, water, and stores.
Catamaran: Twin-hull vessel with high transverse stability.
Cavitation: Vapor bubble formation when local pressure falls below vapor pressure.
Cavitation bucket: Pressure/angle envelope outside which a section cavitates.
Cavitation inception: Speed/loading at which cavitation first appears.
Cavitation number (sigma): Ratio of static-to-vapor pressure margin and dynamic pressure.
Cavitation tunnel: Closed water tunnel for propeller cavitation experiments.
Center of buoyancy (B): Centroid of the displaced volume.
Center of flotation (F): Centroid of the waterplane area.
Center of gravity (G): Mass centroid of the ship.
Center of lateral resistance (CLR): Effective center of underwater side-force.
Chine: Sharp longitudinal corner between hull surfaces, typical of planing craft.
Coefficient of dynamic similarity: Non-dimensional parameter ensuring kinematic-dynamic similitude in model tests.
Comstock righting arm: Cross-curves of stability for free-trim conditions.
Constant-pressure planing: Planing regime with near-uniform bottom pressure.
Container Securing Manual (CSM): Approved manual giving cargo securing forces and limits.
Container slot capacity (TEU/FEU): Volumetric carrying capacity expressed in equivalent units.
Cradle (drydock): Adjustable supports for hull during docking.
Critical speed (vibration): Shaft speed coinciding with a natural frequency.
Cross-curves of stability (KN curves): Plot of KN versus displacement at fixed heel angles.
Cubic number (CN): Product LBD used for empirical lightship and cost relations.
Curve of areas: Plot of sectional area along the length.
Curves of form: Hydrostatic curves versus draft (TPC, MCT1cm, KM, LCB, LCF).

D

Damaged stability: Stability assessment after compartment flooding per SOLAS Ch. II-1.
Damping coefficient (roll): Coefficient governing energy dissipation in roll motion.
Deadweight (DWT): Difference between loaded and lightship displacement.
Deadweight scale: Tabulation of drafts versus deadweight at given densities.
Deck wetness: Frequency of green-water shipping on deck.
Decommissioning weight: Lightship weight after stripping, used in recycling estimates.
Design waterline (DWL): Waterline at design draft.
Detail design: Engineering phase producing fabrication-ready drawings.
Deviation matrix (maneuvering): Linear coefficients of hydrodynamic derivatives.
Diffraction force: Wave force from incident waves with the ship held fixed.
Direct strength analysis: Finite-element check against IACS Common Structural Rules.
Displacement (Δ): Mass of water displaced equal to vessel mass at floating equilibrium.
Displacement-length ratio: Δ/(0.01 L)^3 in long-ton/foot units.
DNV-RP-C205: Recommended practice for environmental conditions and loads.
Doublet (potential flow): Singularity used in panel-method hull representation.
Downflooding angle: Heel at which water enters non-weathertight openings.
Draft (T): Vertical distance from keel to waterline.
Draft mark: Numerals on hull indicating draft.
Drift angle (beta): Angle between hull centerline and velocity vector.
Dynamic positioning (footprint): Watch-circle radius in DP station-keeping.
Dynamic trim: Trim variation with speed due to sinkage moments.

E

Effective horsepower (EHP): Power required to tow the hull at given speed equal to R_T*V.
Effective wake fraction (w): Reduction of inflow velocity at propeller relative to ship speed.
Eigenfrequency (hull girder): Natural frequency of vertical or horizontal hull bending.
Energy Efficiency Design Index (EEDI): IMO design-stage CO2 metric, MEPC.308(73).
Energy spectrum (sea): Distribution of wave energy with frequency, e.g., JONSWAP.
Entrance angle (half angle of entrance, iE): Angle of the waterline at the bow.
Equilibrium polygon: Polar plot of equilibrium drift versus rudder for maneuvering.
Equivalent design wave: Single regular wave reproducing a target long-term load.
Equivalent plate thickness: Smeared thickness of a stiffened panel for FE modeling.
Estimated towing tank power: EHP scaled from model tests via ITTC procedure.
Euler-Bernoulli beam: Beam theory used in classical hull-girder analysis.
Excess wave-making: Resistance beyond a frictional baseline at high Froude number.

F

Fairing: Process of smoothing hull lines.
Fatigue assessment: Cumulative damage check using S-N curves and Miner's rule.
Finite element method (FEM): Discretized PDE solver used for structural analysis.
Flare: Outward slope of side shell above the waterline.
Floodable length: Length of compartment that can be flooded without immersion above margin line.
Form factor (1+k): Multiplier on frictional resistance accounting for form effects.
Forward perpendicular (FP): Vertical line at the intersection of waterline and stem.
Frame spacing: Longitudinal distance between transverse frames.
Free surface correction: Reduction in GM due to liquid free surface in tanks.
Freeboard: Distance from waterline to freeboard deck, governed by the Load Lines Convention but referenced in SOLAS.
Freeboard deck: Uppermost continuous deck per the Load Line Convention.
Frequency-domain seakeeping: Linear motion analysis using response amplitude operators.
Friction line (ITTC-57): CF = 0.075/(log10 Re - 2)^2.
Froude number (Fn): V/sqrt(gL), governing wave-making similitude.
Froude scaling: Test method preserving Fn between model and ship.
Full-form ship: Vessel with high CB, typical of tankers and bulkers.

G

Garbage chute (weight item): Outfitting item entered in weight estimate.
GM (metacentric height): Distance from G to transverse metacenter M.
Gough-Joukowski transform: Conformal mapping used in 2D foil section analysis.
Grim vane wheel: Free-rotating downstream vane wheel for propulsive improvement.
Gross tonnage (GT): Volumetric measure per ITC 1969 GT = K1*V.
Grosvenor curves: Empirical resistance correlations for fishing vessels.
Group velocity (waves): Speed at which wave-group energy propagates.
Gyradius: Radius of gyration about a principal axis.
GZ curve: Static righting arm versus heel angle.

H

Half-breadth plan: Top view of waterlines, half-breadths shown.
Heave: Vertical translational motion.
Heel: Transverse inclination of the vessel.
Helicoidal pitch: Geometric pitch of a propeller blade section.
Helmholtz resonance (moonpool): Vertical oscillation of water column in a moonpool.
Holtrop-Mennen method: Statistical resistance and powering prediction.
Hopper (bulk carrier): Sloped lower wing structure forming cargo hold.
Hovgaard's experiment: Classical demonstration of free-surface effect.
Hughes friction line: CF formulation with form-factor approach.
Hull girder section modulus (Z): Bending section modulus at deck and keel.
Hull vibration mode: Natural vibration shape of the global hull girder.
Hydrodynamic derivatives: Coefficients Yv, Nr, etc. used in maneuvering equations.
Hydrofoil: Lifting surface that supports a hull above the water.
Hydrostatic curves: Curves of form versus draft.

I

IACS Common Structural Rules (CSR): Harmonized rules for bulk carriers and tankers.
IACS Recommendation 34: Standard wave data for North Atlantic.
IACS UR S11: Unified requirement on longitudinal strength.
IACS UR S21: Unified requirement on hatch cover strength.
Incremental hull resistance: Resistance increment from fouling and roughness.
Induced drag (foil): Drag due to trailing-vortex circulation.
Initial stability: Stability range described by GM at small heel.
Intact stability code (2008 IS Code): IMO mandatory intact stability requirements.
Inviscid flow: Idealized flow neglecting viscosity.
ISO 19030: Hull and propeller performance measurement.
ISO 7919: Mechanical vibration of non-reciprocating machinery shafts.
ITTC-57 line: International friction correlation line.
ITTC-78 powering procedure: Standard model-to-ship powering extrapolation.

J

Jet thrust deduction: Thrust loss in waterjet systems analogous to t.
Jib stay loads (yacht NA): Rigging loads transferred to deck and hull structure.
Johnson 4-parameter distribution: Statistical model used for wave amplitudes.
JONSWAP spectrum: Joint North Sea Wave Project spectral form.

K

K-omega (turbulence model): Two-equation RANS closure used in CFD.
Karman-Trefftz profile: Cusped airfoil family used as analytical NA test cases.
Keel block layout: Arrangement of keel and side blocks for drydocking.
Kelvin wave pattern: Characteristic 19.47° wake pattern from a moving disturbance.
Keuning hull series: Delft systematic series for planing hulls.
Kinematic viscosity (nu): Ratio mu/rho used in Re calculations.
KN curve: Cross-curve of stability with reference at the keel.
KORT nozzle: Accelerating ducted-propeller nozzle.
KRISO Container Ship (KCS): Benchmark hull form for CFD validation.
KVLCC2: KRISO Very Large Crude Carrier benchmark hull.

L

Lateral plan (sail NA): Underwater profile area used for sail balance.
Length between perpendiculars (LBP): Length from FP to AP.
Length on waterline (LWL): Length measured at the design waterline.
Length overall (LOA): Maximum length including overhangs.
Lewis form: Two-parameter family of cross sections used in strip theory.
Lift coefficient (CL): Non-dimensional foil lift.
Lifting line theory: Prandtl theory for slender lifting foils and propellers.
Lightship: Vessel mass excluding cargo, fuels, water, stores, and persons.
Lines plan: Drawing of body, sheer, and half-breadth views.
Load line: Statutory waterline mark per ICLL 1966.
Longitudinal center of buoyancy (LCB): Longitudinal centroid of underwater volume.
Longitudinal center of flotation (LCF): Centroid of waterplane area.
Longitudinal center of gravity (LCG): Longitudinal centroid of mass.
Longitudinal framing: Primary framing oriented along the length.
Longitudinal metacenter (ML): Metacenter for trimming moments.
Longitudinal stability: Stability for trim, governed by GML.

M

Maierform: Classic full-form hull with characteristic bow.
Maneuvering Standard (MSC.137(76)): IMO standard ship maneuverability criteria.
Margin line: Reference line 76 mm below bulkhead deck for floodable length.
MARIN: Maritime Research Institute Netherlands hydrodynamic facility.
Mass moment of inertia (Ixx, Iyy, Izz): Rotational inertia about principal axes.
Maximum righting arm: Peak value of GZ on the stability curve.
MCT1cm: Moment to change trim 1 cm.
Metacenter (M): Intersection of buoyancy verticals at small heel.
Metacentric radius (BM): I_T/V, transverse moment of waterplane area over volume.
Michell's integral: Linear theory of wave-making resistance for thin ships.
Model basin: Towing tank with carriage and instrumentation.
Modulus of section (Z): Hull-girder bending strength parameter.
Moment of inertia of waterplane (IT, IL): Used in BM and BML.
Morison equation: Drag-plus-inertia force on slender cylinders.
Multi-body hydrodynamics: Interaction analysis between two or more floating bodies.

N

Naval Hydrodynamics Symposium: ONR-sponsored series of NA conferences.
Net tonnage (NT): Volumetric earning-capacity tonnage per ITC 1969.
Newman-Tuck slender body theory: Slender-ship theory for wave-making and motions.
Noise emission to water (URN): Underwater radiated noise per DNV SILENT class.
Nominal wake: Wake measured at the propeller plane without the propeller.
Non-dimensional pitch (P/D): Propeller pitch normalized by diameter.
Norrbin's nonlinear model: 1-DOF yaw equation for maneuvering.
Numerical towing tank: Full RANS simulation of a self-propelled ship.

O

Oblique sea: Wave heading other than head or following.
Offsets table: Tabulated half-breadths defining hull lines.
One-meter trim moment: Numerical synonym for MCT.
Open-water diagram: KT, KQ, eta_O versus J for a propeller in open water.
Operability envelope: Sea-state limits for mission performance.
Orcaflex: Time-domain dynamic-analysis code for offshore systems.

P

Panel method: Discretization of body surface with sources/dipoles for potential flow.
Parabolic wedge waterline: Wigley hull form used as analytical benchmark.
Parametric roll: Resonant roll growth in head/following seas due to GM variation.
Permeability (compartment): Fraction of volume floodable in damage stability.
Pierson-Moskowitz spectrum: Fully developed sea spectrum.
Pitch (motion): Rotational motion about the transverse axis.
Pitch (propeller): Axial advance per revolution at a section.
Pitch-diameter ratio (P/D): Propeller geometric parameter.
Pivot point: Apparent center of rotation during a turn.
Planing: Hydrodynamic lift regime above hump speed.
Plate field: Stiffened-panel zone of the structural model.
Polar moment of inertia: Used in torsional hull-girder analysis.
Prandtl-Glauert correction: Compressibility correction not used in NA but in air-side analysis.
Pressure pulse (propeller): Hull-surface pressure fluctuation from blade passage.
Prismatic coefficient (CP): Volume divided by midship-section area times length.
Propeller boss cap fin (PBCF): Energy-saving boss cap with fins.
Propeller cavitation criteria (Burrill): Empirical chart of thrust coefficient and cavitation number.

Q

Q-criterion (CFD): Vortex identification method.
Quasi-propulsive coefficient (eta_D): PE/PD overall propulsive efficiency.
Quasi-static heel: Heel under slowly varying loads, ignoring dynamics.

R

Radiation force: Force on a body from its own induced waves.
Random decrement technique: Method for extracting damping from random vibration.
Rankine source method: Free-surface panel method using Rankine sources.
RAO (Response Amplitude Operator): Linear transfer function of motion to wave amplitude.
Reach (sailing NA): Geometric parameter in stability calculations.
Real-time hull monitoring: Strain-gauge-based hull-stress monitoring system.
Relative wind (sail NA): Vector sum of true wind and boat velocity.
Residuary resistance (RR): Resistance after subtracting frictional component.
Resistance coefficient (CT, CF, CR, CA): Components in ITTC-78 procedure.
Reynolds number (Re): VL/nu, governing viscous similitude.
Reynolds-Averaged Navier-Stokes (RANS): Steady or unsteady turbulent flow solver.
Righting arm (GZ): Horizontal distance between weight and buoyancy verticals at heel.
Righting moment: Δ*GZ, restoring moment at given heel.
Roll: Rotational motion about the longitudinal axis.
Roll damping coefficient: Decay parameter from inclining or free-decay tests.
Roughness allowance (CA): Correlation allowance for ship-scale roughness.

S

Sankey diagram (power): Visualization of energy losses in a propulsion plant.
Sectional area curve: Distribution of immersed area along the length.
Self-propulsion test: Model test with operating propeller measuring delivered power.
Series 60: Classic systematic merchant-ship resistance series.

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