Extended Operational and Trade Vocabulary

Propellers, Stern Gear and Shaft Lines glossary

The propeller and shaft-line vocabulary: accelerating ducts (Kort 19A), the advance coefficient J and the Wageningen B-series polynomials, acoustic signature from cavitation and blade rate, and the stern-tube, bearing, and seal terms. Grounds each term in the propeller hydrodynamics or the stern-gear arrangement it belongs to.

468 defined terms.

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

A

Abaft the propeller: Positional reference for any structure located astern of the propeller disc, including the rudder horn, rudder, and stern flap.
Accelerating duct: Annular nozzle profile (Kort 19A family) that accelerates flow into the propeller, increasing bollard thrust at low advance ratios.
Acoustic signature: Underwater noise spectrum radiated by the propeller and shaft line, governed by cavitation, blade rate, and shaft eccentricity.
Advance coefficient J: Non-dimensional propeller parameter J = Va / (n D), where Va is speed of advance, n is shaft rate, and D is diameter.
Advance ratio: Synonym for J used in open-water diagrams and Wageningen B-series polynomials.
Aft peak bulkhead: Watertight boundary forward of the stern tube compartment, supporting the inboard end of the stern-tube assembly.
Aft seal (stern tube): Sealing assembly at the propeller end of the stern tube preventing oil egress and seawater ingress.
Aft stern tube bearing: Long, propeller-side bearing that carries the bulk of the static and dynamic propeller weight reaction.
Air drawing: Ventilation phenomenon in which atmospheric air is sucked down to a lightly submerged propeller, collapsing thrust.
Air injection (rudder): Becker technique of injecting air at the rudder leading edge to mitigate rudder cavitation erosion.
Air lubrication interaction: Effect of hull air-lubrication bubbles passing through the propeller disc, altering inflow density and cavitation behavior.
Akzo Nobel Intersleek: Foul release coating frequently specified on propeller blades to reduce roughness-related efficiency loss.
Alpha Lubricator: MAN ES electronically controlled cylinder lubrication system relevant to the prime mover driving the shaft line.
Andritz Hydro: Austrian manufacturer of large cast and welded propellers and hydraulic machinery, including marine CP units.
Angle of attack (blade section): Geometric angle between the local inflow and the chord line of a propeller blade section.
Anti-singing edge: Chamfered or beveled trailing edge geometry applied to suppress vortex-shedding tonal noise (propeller singing).
Aquamaster: Original Rauma-Repola azimuth thruster line, later Rolls-Royce and now Kongsberg, widely used on tugs and OSVs.
Aramid composite shafting: Non-metallic intermediate shafting based on aramid or carbon-fiber composites used in some naval and yacht applications.
Area ratio (Ae/Ao): Ratio of expanded blade area to disc area, a primary cavitation criterion in B-series selection.
Astern thrust: Thrust generated when the propeller turns in reverse rotation (FPP) or with negative pitch (CPP).
Asymmetric stern: Hull form with port/starboard asymmetry tuned for propeller wake.
Athwartship line shaft alignment: Lateral alignment check performed in addition to vertical sag-and-gap to verify shaft centerline in plan view.
Axial bearing clearance: Permissible axial play of the shaft line at the thrust block, measured at the thrust collar.
Axial thrust (propeller): Net longitudinal force delivered by the propeller and transferred through the thrust block to the hull.
Azimuth Thruster: Propulsion unit rotating 360 degrees about a vertical axis to direct thrust in any horizontal direction.
Azipod: ABB podded electric propulsor with the motor inside a submerged pod, used widely on cruise ships, icebreakers, and shuttle tankers.
Azipod D, M, XO, XL: Specific Azipod product variants ranging from drive-through gearing (D) to direct-drive megawatt-class XL units.
Azipull: Rolls-Royce/Kongsberg pulling-type azimuth thruster with a Z-drive gearbox and a tractor propeller.

B

B4-70: Wageningen B-series propeller designation indicating four blades and an expanded area ratio of 0.70.
B5-75: Five-blade Wageningen B-series propeller with Ae/Ao = 0.75, common for merchant ship preliminary design.
Back cavitation: Vapor cavity on the suction (back) side of the blade caused by low local pressure.
Back of blade: Suction side of the propeller blade, where sheet and tip vortex cavitation usually originate.
Backflushing (stern tube): Operation of reversing or flushing stern-tube oil to clear contamination and water ingress.
Backing thrust ratio: Astern thrust as a fraction of ahead thrust at equal shaft power, typically 0.6 to 0.8 for FPP merchant ships.
Balanced rudder: Rudder with a portion of its area forward of the stock to reduce required steering torque, relevant to propeller-rudder interaction.
Bare hull resistance: Calm-water resistance excluding appendages.
Becker Mewis Duct: Pre-swirl wake-equalizing duct with internal fins, developed by Becker Marine Systems, fitted ahead of the propeller.
Becker rudder (flap rudder): High-lift articulated rudder with a trailing flap linked to the main blade, increasing maximum lift coefficient.
Becker Twisted Fin: Pre-swirl fin device installed forward of the propeller to recover rotational energy and improve efficiency.
Becker Twisted Rudder: Rudder with a leading edge twisted to match the propeller slipstream rotation, reducing rudder cavitation.
Bending moment (shaft): Internal moment in the shaft line arising from propeller weight, hydrodynamic loads, and alignment offsets.
Berg Propulsion: Swedish manufacturer of controllable pitch propellers, transverse thrusters, and propulsion control systems, owned by Caterpillar.
Bevel gear (Z-drive): Spiral bevel gear set used in azimuth thrusters and Z-drives to turn drive through 90 degrees, twice in Z configuration.
Bilge keel interaction: Influence of bilge-keel-generated vorticity on the propeller wake field, addressed in CFD wake studies.
Blade area ratio (BAR): Common term for Ae/Ao, the expanded blade area divided by disc area.
Blade cup: Local trailing-edge curvature on high-speed and surface-piercing propellers, increasing effective pitch.
Blade frequency: Excitation frequency equal to shaft rate multiplied by number of blades (Z f1), a principal hull vibration source.
Blade harmonics: Multiples of blade frequency (2Z, 3Z, etc.) excited by non-uniform wake and cavitation.
Blade outline: Planform shape of the blade, including skewed, raked, Kappel, and tip-loaded variants.
Blade rake: Inclination of the blade reference line forward or aft of the propeller plane, influencing hub-clearance and cavitation onset.
Blade root fillet: Generous radius transition between blade and hub, designed to limit stress concentrations.
Blade section: Two-dimensional hydrofoil profile at a given radius, typically NACA 16 or NACA 66 modified families.
Blade skew: Circumferential offset of blade sections in the direction of rotation, used to reduce blade-rate forces.
Blade tip clearance: Radial gap between the propeller tip and the hull or duct inner surface, a key vibration parameter.
Blade-rate pressure pulse: Pulsating pressure on the hull above the propeller at frequency Zn, the dominant excitation in conventional sterns.
Bollard pull: Tug pulling force in tonnes.
Boring bar (stern tube): Long-line boring tool used to machine stern-tube and strut bores in single setup for concentricity.
Bossing: Faired housing around shaft exit on twin-screw vessels.
Bow thruster shaft (Z-drive): Vertical shaft in a tunnel thruster transmitting power from the in-hull motor or engine.
Bronze propeller: Cast manganese bronze, nickel aluminum bronze (NAB), or manganese aluminum bronze (MAB) propeller per ISO 484.
Brunvoll: Norwegian manufacturer of tunnel thrusters, azimuth thrusters, and CP propeller systems for offshore vessels.

C

CAD-CAM blade machining: Five-axis milling of bronze propeller blades to ISO 484 Class S or Class I tolerances.
Cap (propeller boss cap): Streamlined or finned cap fitted to the aft end of the hub to recover hub-vortex energy.
Capstan effect (shaft seal): Frictional drag generated by lip seals wrapping the shaft liner, a factor in seal life calculations.
Cathodic protection (shaft): Galvanic or impressed current system protecting the shaft, propeller, and rudder from corrosion.
Cavitation bucket: Pressure/angle envelope outside which a section cavitates.
Cavitation erosion: Material loss on blade or rudder surfaces caused by repeated cavity collapse implosions.
Cavitation inception: Speed/loading at which cavitation first appears.
Cavitation number sigma_n: Non-dimensional pressure parameter (p - pv) / (0.5 rho n^2 D^2), used in propeller cavitation diagrams.
Cavitation tunnel: Closed water tunnel for propeller cavitation experiments.
Cedervall: Swedish manufacturer of seawater-lubricated stern-tube bearings and rope guards, now part of Wartsila.
CFD self-propulsion: Numerical simulation coupling the hull, propeller (actuator disc or sliding mesh), and free surface to predict delivered power.
Chord length (blade): Straight-line distance from leading to trailing edge of a blade section.
Cloud cavitation: Bubbly downstream collapse region trailing a sheet cavity, principal driver of erosion.
Co-rotating propellers: Two propellers on parallel shafts turning in the same direction, distinguished from contra-rotating arrangements.
Cold setting (alignment): Static alignment with the ship afloat and machinery cold, the usual reference state for sag-and-gap measurements.
Combinator mode (CPP): CPP control mode in which pitch and shaft speed follow a coordinated curve from a single lever input.
Compensating Nozzle: Asymmetric nozzle (Schneekluth or similar) profiled to compensate hull wake asymmetry.
Composite propeller: Carbon or glass fiber reinforced polymer propeller, offered for example by Airborne and Solas.
Concentricity (stern tube): Alignment of stern-tube bore axis with the engine output flange, verified by laser or piano wire.
Cone (propeller): Tapered portion of the tailshaft on which the propeller hub is keyed or keyless-mounted.
Contra-rotating propellers (CRP): Two coaxial propellers rotating in opposite directions, recovering slipstream rotation; in service on some IHI tankers and Volvo Penta IPS.
Controllable-pitch propeller (CPP): Propeller with hydraulic blade-pitch control.
Coupling bolts (intermediate shaft): Fitted or hydraulically pretensioned bolts joining shaft flanges, designed for torque, bending, and astern shock.
Coupling flange (forged integral): Flange machined integrally with the shaft forging, avoiding shrink-fit coupling risks.
CPP hub mechanism: Internal crank-and-yoke or sliding-block linkage converting OD-box axial servo motion into blade rotation.
CPP oil distribution box (OD-box): Stationary-to-rotating oil transfer unit feeding hydraulic oil to the hub servo through the hollow shaft.
Cradle bearing (stern tube): White-metal half-bearing supporting the shaft inside an oil-lubricated stern tube.
Critical speed (shaft): Rotational speed coinciding with a lateral natural frequency of the shaft line, to be avoided in service range.
Crowned thrust pad: Slightly convex tilting pad surface promoting hydrodynamic film formation in Michell-Kingsbury thrust bearings.
CRP-Azipod: Combined shaft propeller and aft Azipod arrangement creating a contra-rotating effect, used on Mitsui shuttle tankers.
Cup (blade): Trailing-edge curvature added to high-performance propellers to increase effective pitch and delay back cavitation.

D

D/Dh ratio: Diameter to hub-diameter ratio, a geometric parameter of propeller series.
Damen Marine Components: Dutch manufacturer of rudders, nozzles, and steering gear, including Optima and Barke high-lift rudders.
Damen Optima rudder: Twisted high-lift rudder marketed by Damen Marine Components for energy saving.
Decelerating duct (pump-jet): Annular duct profiled to decelerate flow into the propulsor, used on naval submarines for noise reduction.
Delivered power PD: Power delivered to the propeller at the propeller plane, equal to QPD multiplied by 2 pi n.
Demountable propeller blade: Bolted bronze blade arrangement on a separate hub, used on CPPs and some ice-class FPPs.
DESMI: Danish manufacturer of pumps and propulsion components, including aft-peak and stern-tube auxiliaries.
Detuner (torsional): Resilient or hydraulic device tuned to shift a torsional resonance out of the service range.
Diesel-electric drive: Propulsion architecture in which the prime mover drives a generator and the propeller is electrically driven, common with podded propulsors.
DNV CG-0038: DNV class guideline for calculation of shafting and key components, widely referenced for shaft design.
Doxford opposed-piston engine: Historic two-stroke directly coupled to the shaft line on many British-built ships; relevant to legacy torsional vibration cases.
Dry-dock alignment: Cold static alignment with the vessel in dry dock, used as a baseline before afloat verification.
Dual-fuel CPP: CPP whose control algorithm is tuned to match the load curve of dual-fuel main engines.
Ducted propeller: Propeller operating inside a fixed annular nozzle (Kort 19A, 37, or 22), increasing thrust at heavy loading.
Duplex stainless shaft: Tailshaft fabricated from duplex stainless steel (e.g., UNS S31803) for seawater-lubricated installations.
Dynamic balancing (propeller): Two-plane balancing of large propellers performed before fitting, mainly for high-speed and naval applications.
Dynamic positioning thruster: Azimuthing or tunnel thruster integrated in a DP system to maintain station against environmental loads.

E

EagleBurgmann ESPEY: Segmented mechanical seal series used as stern-tube and bulkhead shaft seals.
Eaton seal: Lip-type stern-tube seal historically supplied by Eaton, now part of broader rotary seal lines.
Effective horsepower (EHP): Power required to tow the hull at given speed equal to R_T*V.
Effective wake fraction w_e: Wake fraction derived from thrust or torque identity in self-propulsion analysis.
Efficiency, behind hull (eta_B): Propeller efficiency in the actual wake, equal to eta_0 multiplied by relative rotative efficiency eta_R.
Efficiency, hull (eta_H): Ratio (1 - t) / (1 - w), where t is thrust deduction and w is wake fraction.
Efficiency, open water (eta_0): J KT / (2 pi KQ), the propeller efficiency measured in uniform inflow.
Efficiency, propulsive (eta_D): Quasi-propulsive coefficient eta_H multiplied by eta_0 multiplied by eta_R.
Efficiency, relative rotative (eta_R): Correction accounting for differences between open-water and behind-hull torque coefficients.
Elastic coupling: Resilient torsional element (Vulkan, Centa, Geislinger) inserted in the shaft line to detune torsional vibration.
Elastomeric stern tube bearing: Water-lubricated bearing using elastomeric or polymer staves (Thordon, Cutless), supplanting lignum vitae in modern designs.
Electric propulsion converter: Power electronics module (VFD) feeding the propulsion motor of a podded or shaft-mounted electric drive.
EMD 645/710 (marine): Two-cycle locomotive-derived engines used in some naval and ferry shaft-line installations.
Energy-saving device (ESD): Generic term covering pre-swirl fins, ducts, PBCFs, and hubcap rudder bulbs that improve propulsive efficiency.
Engine alignment (with shaft): Adjustment of the engine on its bedplate so that its output flange matches the intermediate shaft line.
EPDM stave (water-lubricated bearing): Elastomer stave geometry in a water-lubricated stern-tube bearing, allowing groove cooling and debris flushing.
Erosion test (cavitation): Soft-paint, stencil, or pit-counting procedure used in cavitation tunnels to assess erosion risk on a blade.
Expanded area: Sum of expanded blade-section areas, used to compute Ae/Ao.

F

Face cavitation: Cavitation on the pressure side of the blade, typically near the leading edge at light loads or excessive pitch.
Face pitch: Local pitch of the blade face at a given radius, used in geometric definitions.
Faired skeg: Hydrodynamically faired stern skeg on twin-screw or pod-driven hulls, reducing flow separation into the propeller.
FCP (fixed pitch propeller): Synonym for FPP, a propeller with permanently set blade pitch.
Feathering propeller: Variable-pitch propeller able to set blades parallel to the flow for minimum drag, used on auxiliary sailing yachts.
Final drive (Z-drive): Lower bevel gear of a Z-drive in the submerged gear housing, coupled to the propeller shaft.
Finite element propeller analysis: FEA of bronze or composite blades for stress, deflection, and natural frequency under hydrodynamic load.
Fishtail rudder: Rudder with a flared trailing edge profile increasing maximum lift, marketed by Schilling and others.
Five-blade FPP: Conventional merchant ship propeller arrangement reducing blade-rate pressure pulses relative to four-blade designs.
Fixed Pitch Propeller (FPP): Propeller with non-adjustable blades, used on many conventional tugs.
Flap rudder: Rudder with a hinged trailing flap (Becker, Promac, JASTRAM), increasing lift at given helm angle.
Flettner thrust effect: Cross-flow thrust contribution discussed in the context of rotor sails interacting with propulsor loading.
Flexible coupling: Resilient torsional or torsionally rigid coupling joining engine and gearbox or gearbox and shaft.
Flow straightener (post-swirl): Fixed-blade device aft of the propeller (e.g., rudder bulb fins, Mitsubishi MT-FIN) recovering rotational energy.
Force coefficient (KT, KQ): Non-dimensional thrust and torque coefficients defined as T / (rho n^2 D^4) and Q / (rho n^2 D^5).
Forged steel shaft: Tailshaft or intermediate shaft forged from carbon-manganese or alloy steel per IACS UR M68.
Forward seal (stern tube): Inboard end seal of the stern tube, separating oil sump from engine-room atmosphere.
Four-blade propeller: Common arrangement for merchant ships, balancing efficiency and unbalanced moments.
Free-running propeller test: Open-water propeller test in a towing tank with the propeller running without hull interaction.
Frequency-converter drive: Variable-frequency drive used in electric shaft or podded propulsion to vary motor speed.
Friction torque (bearings): Hydrodynamic or boundary friction torque in stern-tube and intermediate bearings, contributing to shaft losses.
Front cap (CPP): Forward end cover of the CPP hub, often containing piston and feedback rod.
Full-form bulker stern: Stern shape with high block coefficient, producing strong wake non-uniformity and demanding skewed propellers.

G

Gawn series: Propeller series tested by R. W. L. Gawn at Haslar in the 1950s, used for naval and high-speed craft preliminary design.
Gear coupling: Toothed coupling allowing slight misalignment between connected shafts, used in some industrial-style shaft lines.
Gear reduction (marine): Reduction gear (single or twin-input) matching engine speed to propeller speed, by makers such as Reintjes, ZF, Renk, MAN, Lufkin.
Geislinger coupling: Steel-spring torsional coupling used in medium-speed and high-speed shaft lines for torsional detuning.
Generative blade design: Parametric blade definition (pitch, camber, skew, rake distributions) used in CFD-driven propeller optimization.
Geometric pitch: Theoretical advance per revolution if the blade moved through a solid medium without slip.
Glass-reinforced epoxy (GRE) duct: Composite construction option for Kort nozzles in workboat and aquaculture vessels.
Goose neck shaft (yacht): Curved or articulated shaft line found in some yacht and surface-drive installations.
Grim vane wheel: Free-rotating downstream vane wheel for propulsive improvement.
Grimspol propeller: Trade name historically used for some Grim-vane and ducted propeller configurations.
GTW (Wartsila stern tube): Wartsila water-lubricated stern-tube product family, formerly Cedervall.
Guide vane (pre-swirl): Stationary blade ahead of the propeller imparting counter-rotational flow to recover swirl energy.

H

HamiltonJet waterjet: Family of waterjets from CWF Hamilton (New Zealand), used on fast craft as an alternative to propellers.
Hatlapa thruster gear: Hatlapa-designed gear units used in some transverse thruster arrangements; brand now within MacGregor.
HHI propeller works: Hyundai Heavy Industries propeller foundry and CFD group producing large bronze propellers.
High-skew propeller: Propeller with skew angle typically exceeding 25 degrees, used to reduce blade-rate forces and cavitation impact.
Hollow shaft: Bored intermediate or tailshaft, mandatory for CPP installations to pass servo oil and pitch feedback.
Hot oil flushing: Pre-commissioning procedure circulating heated oil through stern-tube and lube-oil piping to remove debris.
Hub cap fin (PBCF): Mitsui propeller boss cap fins recovering hub-vortex energy; one of the most installed ESDs.
Hub cone: Conical aft portion of the propeller hub, downstream of the blade roots.
Hub ratio (d/D): Ratio of hub diameter to propeller diameter, larger in CPP than in FPP due to internal mechanism.
Hub vortex: Coherent vortex shed from the propeller hub on the centerline, associated with hub erosion and rudder cavitation.
Hubless rim-drive thruster: Electric thruster with the motor stator in a duct rim and blades cantilevered to a hubless ring.
Hull efficiency eta_H: Defined as (1 - t) / (1 - w), accounting for thrust deduction and wake fraction.
Hull-mounted shaft brackets: Single- or twin-arm A-brackets and V-brackets supporting exposed shafts on twin-screw ships.
HVAF thermal spray (shaft): High-velocity air-fuel thermally sprayed coating used to repair shaft journal wear at seal positions.
Hyflex propeller alloy: Trade designation for certain high-strength nickel-aluminum-bronze alloys used in propeller casting.

I

IACS UR M51: Unified requirement for propulsion shafts and propellers, defining minimum diameter formulae.
IACS UR M68: Unified Requirement on dimensioning and arrangement of starting air systems.
Ice-class propeller: Propeller designed to IACS Polar Class or Finnish-Swedish ice class rules, with thicker sections and reinforced root.
ICR (ice class root): Increased blade root thickness specification on ice-strengthened propellers.
ICR design loads: Polar Class blade design loads per IACS UR I3, calibrated against measured ice-block impacts.
Idle gear (azimuth): Idler gear in some azimuth thruster gear trains used to reverse rotation sense or split torque.
IHI HZ Fin: Pre-swirl reaction fin developed by IHI, fitted on bulkers and tankers ahead of the propeller.
IHI-Marine United: Japanese builder associated with contra-rotating propeller systems on shuttle tankers.
Inboard shaft bearing: Intermediate bearing inside the engine room, usually a white-metal, oil-ring or oil-bath plain bearing.
Inclined shaft: Shaft line installed at an angle to the baseline, common on fast craft to reduce hull penetration depth.
Induced velocity: Velocity field induced by the propeller on its own and the surrounding flow, central to lifting-line and lifting-surface theory.
Inflow velocity field: Time-averaged and unsteady velocity components entering the propeller disc, measured by LDV or PIV.
Insulated coupling: Flange insulation kit isolating the propeller from the hull electrically to protect ICCP systems.
Intermediate bearing: Shaft-line bearing between the engine output and the stern-tube assembly, supporting the intermediate shaft.
Intermediate shaft: Section of propeller shafting between thrust shaft and tail shaft.
ITTC 1957 friction line: Standard skin-friction line used in ITTC powering predictions, the framework within which propeller open-water data are scaled.
ITTC propeller open-water test procedure: Standardized procedure (7.5-02-03-02.1) for towing-tank open-water propeller tests.
ITTC scaling (propeller): Procedure correcting model open-water data for Reynolds number to full scale.

J

J value (advance coefficient): J = Va / (n D), the ordinate of open-water KT and KQ curves.
Jack-up method (alignment): Shaft alignment technique measuring bearing reactions by hydraulic jacking to verify load distribution.
JASTRAM steering gear: German maker of steering gears and rudders, including high-lift designs for inland and seagoing vessels.
Journal bearing (stern tube): Plain hydrodynamic bearing in which the shaft journal rides on an oil or water film, the dominant stern-tube bearing type.

K

Kamewa CP propeller: Kamewa controllable pitch propeller series, now within Kongsberg Maritime.
Kamewa S-thruster: Steerable thruster line originating with Kamewa, continued under Rolls-Royce and Kongsberg.
Kappel propeller: Tip-loaded propeller with smoothly curved tip developed by J. J. Kappel and MAN Diesel & Turbo (MAN ES).
Karman vortex shedding (rudder): Periodic vortex shedding from rudder trailing edges responsible for rudder singing.
Kawasaki Heavy Industries (KHI): Builder of Moss spherical LNG carriers and supplier of steam turbines for many older LNGCs.
Kemel seal: Kobelco Eagle Marine (Kemel) shaft seals, including air-type and oil-type stern-tube seals.
Key (propeller): Parallel key historically used to lock keyed propellers to the cone; superseded by keyless hydraulic fits on most large ships.
Keyless propeller fit: Shrink fit between propeller hub and shaft cone, set by hydraulic pull-up per ISO 2503/maker procedure.
Kingsbury thrust bearing: Tilting-pad thrust bearing pioneered by Albert Kingsbury, mechanically related to Michell pads.
Kitchen rudder: Twin-clamshell directional rudder used historically on launches, providing thrust direction without propeller reversal.
Knuckle (azimuth steering): Mechanical interface between steering tube and propeller gear housing in a steerable thruster.
Kobelco propeller: Propellers from Kobelco group facilities, including stern-tube and seal products under the Kemel brand.
Kongsberg Maritime: Norwegian supplier of bridge, automation and dynamic positioning systems.
KORT nozzle: Accelerating ducted-propeller nozzle.
KT-KQ diagram: Open-water propeller chart plotting KT, 10 KQ, and eta_0 against J.

L

Laser shaft alignment: Optical method using a laser source and target to measure shaft straightness and bearing offsets.
Lateral vibration: Whirling vibration of the shaft line, calculated to ensure adequate margin from running speed.
Lifting line theory: Prandtl theory for slender lifting foils and propellers.
Lifting surface theory: Higher-fidelity propeller theory representing blade chordwise loading by vortex panels.
Light-running margin: Margin between MCR shaft speed and the propeller-curve intersection in the calm-water condition.
Lignum vitae bearing: Traditional wood stave water-lubricated stern-tube bearing material, largely replaced by elastomers and polymers.
Line bore: Long machining operation aligning multiple bores (stern tube, strut, A-bracket) on a single axis.
Line shaft seal: Bulkhead penetration seal in the shaft line, used where the shaft passes through the aft peak bulkhead.
Lloyd's Register Rules Pt 5 Ch 8: LR rules covering shafting design and shaft alignment requirements.
Lock-and-key (CPP): Failsafe locking system fixing CPP blade angle if hydraulic control is lost.
Lubrication oil unit (stern tube): Header-tank or pump unit maintaining stern-tube oil pressure above sea pressure at the aft seal.
Lufkin marine gear: Lufkin Industries (now RBI Bearings/Siemens) reduction gears used in some U.S. vessels.

M

MacGregor steering gear: Steering gear and rudder line within Cargotec, supplied to numerous workboat and merchant projects.
Magnaflux inspection (shaft): Magnetic particle non-destructive examination of forged shafts and propeller cones.
MAN ES Alpha CPP: MAN Energy Solutions Alpha controllable pitch propeller, the main MAN CPP product, manufactured in Frederikshavn.
MAN ES Kappel propeller: Tip-modified FPP/CPP blade design jointly developed by MAN ES and J. J. Kappel.
MAN ES Mark series propeller: Family of FPP designs offered as part of MAN ES propulsion packages.
MAN ES rudder bulb: Streamlined hub-aligned bulb installed on the rudder behind the propeller to recover hub-vortex energy.
MAN Holeby auxiliary engine: Auxiliary genset family relevant to electric drive of azimuth thrusters and pods.
MARIN (Wageningen): Maritime Research Institute Netherlands, custodian of the Wageningen B, C, Ka, and Kd propeller series.
Marine Propulsion Holland (MPH): Dutch supplier of CPP systems and steering gears for workboat and inland markets.
Mecklenburger Metallguss (MMG): German propeller foundry casting some of the world's largest bronze propellers, including 11 m diameter units.
Megi mount: Resilient mount type used in propulsion auxiliaries; relevant for vibration isolation though not in the main shaft path.
Membrane coupling: Diaphragm-style flexible coupling accommodating axial and angular misalignment in some gear-driven shaft lines.
Merritt-Brown gear: Historic naval reduction gear designs informing modern double-reduction marine gearboxes.
Mewis Duct: Pre-swirl wake-equalizing duct developed by Friedrich Mewis and Becker Marine Systems, widely retrofitted on tankers and bulkers.
Michell pad: Tilting-pad thrust bearing element invented by Anthony Michell, the principal pad geometry in marine thrust blocks.
Misano polymer bearing: Generic example category of polymer-stave stern-tube bearings; not a recognized class-approved product (omit if uncertain).
Mitsubishi Heavy Industries propellers: MHI propeller line, including high-skew designs and the MT-FIN energy-saving fin.
MMG Promas-style designs: Custom integrated propeller-hub-rudder designs cast by MMG for major newbuilds.
MT-FIN (Mitsubishi): Reaction fin device installed upstream of the propeller by Mitsubishi to improve wake field.

N

Nakashima Propeller: Japanese propeller foundry (Okayama) producing FPP and CPP blades for merchant and naval vessels.
National Maritime Research Institute (NMRI Japan): Japanese research institute publishing propeller and ESD studies.
Nautican integrated propulsion: Canadian supplier of integrated nozzle-rudder propulsion units for tugs and workboats.
Newton Equipment seal: Generic example, omit if not class-recognized. (Replace with verified maker if known.)
Niigata Z-Peller: Azimuthing propulsion unit.