Extended Operational and Trade Vocabulary

Propellers, Stern Gear and Shaft Lines glossary (page 2)

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 218 on this page (page 2 of 2).

N

Nikkei propeller bronze: Generic descriptor for Japanese-cast NAB propellers; omit unless verified maker name.
Nominal wake fraction w_n: Wake fraction measured without the propeller present.
Non-Newtonian stern-tube oil: Synthetic environmentally acceptable lubricant (EAL) class with shear-thinning behavior, used to satisfy VGP.
Nozzle, decelerating: Annular duct decelerating flow into the propulsor, used on submarine pump-jets for noise control.
Nozzle, fixed: Stationary Kort-type nozzle bolted to the hull on tugs and workboats.
Nozzle, steerable: Pivoting Kort nozzle (e.g., Schottel SRP-type duct) serving as both duct and rudder.

O

OD-box (oil distribution box): Stationary housing transferring servo oil through a rotating shaft to the CPP hub.
Off-design analysis: Propeller performance analysis at operating points other than the design J.
Oil-lubricated stern tube: Stern-tube arrangement with white-metal bearings flooded in lubricating oil, sealed by lip or mechanical seals at both ends.
Open water test: Towing-tank test of a propeller in uniform inflow, generating the open-water diagram.
Open-water diagram: KT, KQ, eta_O versus J for a propeller in open water.
Optimum diameter (B_p chart): Diameter chosen from B_p delta charts (Schoenherr, Bp-delta) for given power, RPM, and ship speed.
OSA Marine propeller drive: Generic descriptor; omit unless verified product line.
Outboard seal: Aft (outboard) stern-tube seal, the principal interface between stern-tube lubricant and seawater.
Outdrive (sterndrive): Inboard-outboard drive integrating a Z-drive in the transom; used on small craft, Mercury and Volvo Penta principal makers.
Overhang (shaft): Cantilevered length of tailshaft beyond the aft stern-tube bearing carrying the propeller weight.

P

PBCF (Propeller Boss Cap Fins): Mitsui (MOL Techno-Trade) finned hub cap recovering hub-vortex energy, with thousands of installations.
Pintle (rudder): Lower hinge pin of a rudder, relevant where rudder horn arrangements interact with the propeller race.
Piston (CPP hub): Hydraulic piston inside the CPP hub translating servo oil pressure into axial motion driving the blade crosshead.
Pitch (P): Axial distance advanced per revolution if the blade screwed through a solid; measured at 0.7R for nominal value.
Pitch angle: Angle the helical pitch surface makes with the propeller plane at a given radius.
Pitch distribution: Variation of pitch with radius across the blade, often non-uniform for performance optimization.
Pitch ratio (P/D): Pitch divided by diameter, a primary geometric parameter in propeller series.
Pod efficiency: Overall efficiency of a podded propulsor, including electric motor, gear (if any), and propeller.
Podded propulsor: Azimuthing propulsion unit with the prime mover inside the submerged pod (Azipod, Mermaid, SSP, Dolphin).
Polymer stern tube bearing: Bearing using polymer (Thordon COMPAC, Cutless XL, Vesconite) staves running on water lubrication.
Pre-swirl device: Energy-saving device imparting counter-rotation to flow entering the propeller (Mewis Duct, IHI HZ Fin, Becker Twisted Fin).
Pre-swirl stator: Energy-saving device with vanes ahead of propeller.
Pressure pulse measurement: Hull-mounted pressure transducer measurement of blade-rate pulses, used to assess vibration risk.
Promas (Kongsberg): Integrated propeller-hub-cap-rudder system marketed by Kongsberg (formerly Rolls-Royce) combining a hub cap and propeller-aligned rudder bulb.
Promas Lite: Retrofit version of Promas adapting existing rudder and propeller arrangements.
Propeller balancing: Static balancing performed during manufacture, with dynamic balancing for high-speed propellers.
Propeller cone: Tapered shaft end on which the propeller hub seats via keyless or keyed fit.
Propeller curve: Power versus shaft speed relationship of the propeller absorbing in service, normally cubic in calm water.
Propeller diameter D: Tip-to-tip diameter of the propeller, the principal geometric parameter.
Propeller drawing in/out (yard procedure): Sequence for fitting or withdrawing the propeller from the shaft cone using a hydraulic pull-up tool.
Propeller efficiency at design point: eta_0 evaluated at the J corresponding to design speed and RPM.
Propeller emergence: Partial emergence of the propeller at light draft or in waves, leading to ventilation and load fluctuation.
Propeller hub: Central body of the propeller, carrying the blades (FPP) or the pitch mechanism (CPP).
Propeller immersion: Distance from waterline to propeller shaft centerline, a major cavitation parameter.
Propeller induced pressure: Unsteady pressure field on the hull from blade passage and cavity volume variation.
Propeller manufacturing standards: ISO 484/1 and 484/2 governing tolerance classes S, I, II, and III.
Propeller pitch verification: On-blade measurement of pitch at multiple radii using a pitch-o-meter or CMM.
Propeller polishing: Hull and propeller maintenance reducing roughness and fuel use.
Propeller rake: Inclination of the blade reference line from the propeller plane.
Propeller shaft (tail shaft): Outermost section of the shaft line carrying the propeller cone, supported by the stern-tube bearings.
Propeller singing: Resonant tonal noise from blade trailing-edge vortex shedding coinciding with a blade natural frequency.
Propeller skew: Circumferential offset of blade reference line in the direction of rotation.
Propeller tip vortex: Helical vortex shed from each blade tip, the seat of tip vortex cavitation.
Propeller weight: Mass of the propeller, relevant to shaft bending moment and stern-tube bearing load.
Propulsive coefficient PC: Ratio of effective horsepower to shaft horsepower, equal to eta_D times shaft transmission efficiency.
PRS (Polski Rejestr Statkow) rules: Polish classification society rules covering shafting and propellers.
Pull-up length (keyless fit): Axial pull-up of the propeller onto its cone needed to develop the design interference per the maker.

Q

Quasi-propulsive coefficient (eta_D): PE/PD overall propulsive efficiency.
Quill shaft: Hollow torsion shaft used in flexible couplings.

R

Rake angle: incline of stacker boom in dry bulk terminals.
Rapson slide: Crosshead arrangement converting hydraulic ram travel into rudder rotation in ram type steering gear.
Reaction fin (Hitachi-Zosen): Pre-swirl stator developed by Hitachi-Zosen and IHI, fitted ahead of the propeller on bulkers and tankers.
Reduction gear: Gearbox lowering engine speed to propeller speed on medium speed installations.
Reintjes: German manufacturer of marine reduction gears for medium- and high-speed propulsion plants.
Relative rotative efficiency eta_R: Ratio of behind-hull torque coefficient to open-water torque coefficient at the same thrust.
Renk thrust bearing: Renk-Maag axial tilting-pad thrust bearing widely used on two-stroke main engines and intermediate shafts.
Reverse-rotation propeller: Propeller designed for left-hand or right-hand rotation, paired in twin-screw installations to balance side forces.
Reynolds number (propeller): Defined on chord length at 0.7R, used in open-water scaling.
Rice husk noise (cavitation): Colloquial description of broadband cavitation noise from intense cloud cavitation.
Rim-driven thruster: Electric motor integrated in a duct rim driving a hubless propeller (Voith Inline Thruster, Brunvoll RDT, Schottel SRT).
Rolls-Royce Mermaid: Podded propulsor (legacy).
Rope guard: Disc or sleeve covering the gap between propeller hub and aft stern-tube seal to prevent rope ingress.
Rotor sail wash interaction: Influence of rotor sail downwash on stern flow; relevant to propeller inflow on retrofits.
RS (Russian Maritime Register): Russian classification society publishing rules for shafting and propellers, including ice classes.
Rubber sleeve seal: Auxiliary rubber sleeve type used as a temporary stern-tube seal for repair at sea.
Rudder bulb: Streamlined bulb on the rudder leading edge aligned with the propeller hub to recover hub-vortex energy.
Rudder horn: Structural rudder support cast or fabricated.
Rudder lift coefficient: Non-dimensional rudder force coefficient, function of rudder angle, profile, and slipstream.
Rudder propeller (Schottel): Schottel term for an azimuth thruster (SRP, STP), where the propeller and duct rotate together for steering.
Run (yard alignment): Trial run after final alignment to verify thermal growth and bearing temperatures.

S

Sag and gap: Pre-bolting measurements of the angular gap and parallel sag between shaft flanges, used in shaft alignment.
Schilling rudder: High-lift rudder developed by Hans Schilling featuring a fishtail trailing edge, allowing improved low-speed maneuvering.
Schottel Pump Jet: Hull-mounted pump-jet thruster from Schottel, used on harbor craft and offshore vessels.
Schottel SCD: Schottel Combi Drive combining an electric motor in a pod with a Z-drive style azimuth unit.
Schottel SRP: Azimuth thruster series.
Schottel STT: Schottel Transverse Thruster (tunnel thruster) product family.
SCRC (Stern Counter Rotating Compact): Mitsubishi compact contra-rotating propeller arrangement (omit if not in service).
Seal air system (stern tube): Compressed-air system pressurizing the aft seal chambers in air-type Kemel and Wartsila seals.
Self-propulsion test: Model test with operating propeller measuring delivered power.
Servo oil pressure (CPP): Hydraulic pressure inside the CPP hub piston, typically 35 to 100 bar depending on size.
Shaft alignment: Engineering process aligning engine, gearbox, intermediate, and tail shaft bearings to acceptable loads and angles.
Shaft bracket (A-bracket): Single- or twin-strut hull appendage supporting the outboard shaft on twin-screw vessels.
Shaft brake: Brake mounted on the intermediate shaft to lock or slow the shaft when needed for maneuvering, common on RoRo and ferry installations.
Shaft current: Stray current flowing through the shaft, mitigated by shaft grounding (slip ring brushes).
Shaft generator: Generator driven by main engine via PTO.
Shaft grounding device: Brush-and-slip-ring arrangement bonding the rotating shaft to the hull for corrosion and electronics protection.
Shaft hammer (defect): Operator term for impacts in the shaft line due to loose flange bolts or coupling damage.
Shaft horsepower (SHP): Power transmitted by the propeller shaft.
Shaft line: Entire rotating assembly from engine or gearbox flange to propeller, including couplings, bearings, and seals.
Shaft locking device: Mechanical pin or shoe used to lock the shaft during sea passage or maintenance, applicable on twin-screw ships sailing single-screw.
Shaft seal: Stern tube seal arrangement, brand examples include Wartsila Sterntube and Simplex Compact.
Shaft sleeve (liner): Bronze or stainless sleeve shrunk on the shaft at the bearing or seal location to provide a renewable wear surface.
Shaft taper: Conical end of the tailshaft on which the propeller hub is fitted.
Sheet cavitation: Stable vapor cavity covering part of the suction side of the blade at moderate cavitation numbers.
Side bearing reaction: Component of stern-tube bearing reaction in the athwartship direction, generally small in aligned shafts.
Single-stern bearing arrangement: Stern-tube design with only the aft bearing, omitting the forward bearing to reduce length.
Sister Block (SKF/SNL): Plummer-block style intermediate shaft bearing, used in some smaller and offshore applications.
Skeg-mounted azimuth (skeg pod): Pod mounted on the leading edge of the skeg in some research and cruise ship installations.
Skew angle: Geometric skew defined as the angle subtended at the shaft axis by the midchord lines at the tip relative to the root.
Skew-induced unsteady loading: Reduction of blade-rate unsteady forces brought about by phased blade entry into the wake peak via skew.
SKF marine bearings: SKF supplies thrust bearings, intermediate plummer-block bearings, and bearing-monitoring sensors for shaft lines.
Slip (apparent): 1 - V / (n P), the apparent slip of the propeller through the water.
Slip ring (shaft grounding): Carbon brush running on a slip ring on the intermediate shaft, bonding shaft to hull electrically.
Slipstream contraction: Diameter reduction of the propeller slipstream downstream of the disc, predicted by momentum theory.
Soft-iron stern-tube bearing (historic): Early stern-tube bearing material, superseded by white metal, lignum vitae, and modern elastomers.
SOLAS Reg II-1: SOLAS chapter referencing propulsion machinery and shaft sealing requirements within machinery space protection.
Sole piece: Forging at the bottom of a horn-supported rudder, sometimes interacting with the propeller race.
Solid coupling: Rigid bolted flange coupling joining shaft sections, the dominant intermediate-shaft coupling type.
Solid forged propeller shaft: Tailshaft made from a single forging, the standard arrangement on most merchant ships.
Spade rudder: Cantilevered rudder without horn support, common on container ships and tankers behind a single propeller.
Specific thrust: Thrust per unit disc area, T / (rho V^2 D^2 pi / 4), used in heavily loaded propeller analysis.
SR thruster (Wartsila SRP): Wartsila steerable thruster series including SRT and SCD lines.
SSP propulsor (Siemens-Schottel): Siemens-Schottel podded propulsor with twin propellers (puller pair), used on the Norwegian coastal route ships.
SSPA (Sweden): Swedish maritime research institute operating towing tanks and cavitation tunnels for propeller research.
Stator vane (post-swirl): Stator located aft of the propeller, recovering rotational kinetic energy from the slipstream.
Steerable Kort nozzle: Kort nozzle rotating with the azimuth thruster, serving as duct and rudder.
Stern bearing wear-down: Measured radial wear of the aft stern-tube bearing, monitored against class poker-gauge limits.
Stern flap: Hull appendage downstream of the transom; not directly part of the propeller, but altering propulsive efficiency on naval ships.
Stern frame: Casting or fabrication forming the stern boss into which the stern tube is inserted.
Stern thruster: Tunnel or azimuth thruster located near the stern for low-speed maneuvering.
Stern tube: Tube housing tail shaft with forward and aft seals and lube oil sump.
Stern tube bearing: Aft propeller-shaft bearing, white-metal or composite.
Stern tube lubricant: Mineral or environmentally acceptable lubricant (EAL) circulated through the stern-tube bearing system.
Stern Tube Seal: Common ingress point requiring salvage attention on grounded vessels.
STG (Schiffbautechnische Gesellschaft): German Society of Naval Architects publishing propeller and ESD research.
Stocznia Gdynia/Crist propellers: Polish propeller foundry capacity used on European newbuilds (omit if unverified).
Stuffing box: Sealing arrangement around shaft penetration of bulkhead.
Supercavitating propeller: High-speed propeller designed to operate with a fully developed cavity on each blade, used on naval high-speed craft.
Surface-piercing propeller: Partially submerged propeller used on fast craft, by Arneson, France Helices, Twin Disc, and others.
Swirl recovery vane: Generic name for a fixed post-propeller vane recovering rotational energy in the slipstream.

T

Tachometer (shaft): Rotational speed sensor on the intermediate shaft, used for control and torsional measurement.
Tail shaft: Aftermost section of propeller shaft.
Tail Shaft Survey: Class periodic survey of tail shaft and stern tube bearings.
Taper (propeller cone): Slope of the tail-shaft cone, typically 1:12 to 1:15 for keyless fits.
Telescope inspection (stern tube): Borescope or telescope visual inspection of bearings through stern-tube oil sight ports.
Tempress thruster (Brunvoll/Schottel): Generic descriptor; omit unless verified maker product.
Thordon COMPAC: Thordon Bearings polymer water-lubricated stern-tube bearing, widely used for seawater-lubricated installations.
Thordon SXL: Thordon non-metallic bearing used in intermediate and rudder applications.
Thordon Thorshield: Thordon shaft cladding system protecting the shaft in seawater-lubricated installations.
Three-blade propeller: Common on small craft and high-speed propellers, offering high efficiency at moderate disc loading.
Thrust bearing: Kingsbury type bearing taking propeller thrust into hull.
Thrust block: Bearing absorbing propeller thrust.
Thrust collar: Forged collar on the shaft transferring axial load to the thrust pads.
Thrust deduction t: Fraction by which propeller-induced pressure reduction increases hull resistance; T(1 - t) = R_T at self-propulsion.
Thrust horsepower (THP): Power equivalent T V_a in the propeller open-water frame.
Thrust meter: Strain-gauge or laser-based thrust measurement device used in shop and sea trials.
Thrust pad temperature monitor: Resistance thermometer in each thrust pad, alarm-tripped to protect against pad wipe.
Tip clearance: Radial gap between propeller tip and hull or duct, a key vibration parameter.
Tip rake propeller (CLT): Contracted and loaded tip propeller by SISTEMAR (Spain), with tip end plates.
Tip vortex cavitation: Cavitation in the helical tip vortex shed from each blade, typically the earliest cavitation form to appear.
Tip-loaded propeller (Kappel): Propeller with smoothly recurved tip loading, designed to recover tip-vortex losses.
Torque (propeller): Shaft torque absorbed by the propeller, equal to KQ rho n^2 D^5 in open water.
Torque meter: Strain-gauge or magneto-elastic device on the intermediate shaft measuring shaft torque continuously.
Torsional vibration: Cyclic twist in shaft system, design limited by class.
Torsional vibration calculation (TVC): Class-approved shafting analysis.
Tracker propeller (azimuth): Tractor-type propeller in front of an azimuth thruster pod (Azipull, ZF AT-series).
Tractor propeller (azimuth): Pulling-type propeller upstream of the pod body in tractor thrusters.
Tunnel thruster: Transverse thruster mounted in a tunnel.
Twin in-and-out (twin-screw rotation): Convention in which port and starboard propellers rotate such that blade tops move outward (or inward) at top dead center.
Twisted leading edge (rudder): Geometry of the Becker Twisted Rudder leading edge matching slipstream swirl.
Two-stroke direct drive: Propulsion arrangement with a low-speed two-stroke directly coupled to the propeller, the dominant ocean-going merchant configuration.

U

U-bracket: Twin-strut shaft bracket used on some twin-screw ships in place of a single A-bracket.
Ulstein UCN propulsion: Ulstein Power & Control historically supplied controllable pitch and azimuth thrusters; some product lines now within other groups.
Underdeck shaft tunnel: Compartment housing the intermediate shaft on some RoRo and naval ships.
Underwater radiated noise (URN): Acoustic emissions from shipping addressed by MEPC.1/Circ.906 (2023) revised guidelines.
Universal hydraulic pull-up tool: Jacking tool used to fit and remove keyless propellers from their cones.
Unsteady blade loading: Time-varying blade force generated by passage of the blade through a non-uniform wake.
Upper bevel (Z-drive): Upper bevel gear set in a Z-drive azimuth thruster, in the steering tube above the slewing bearing.
US 105/155/255 thruster (Rolls-Royce/Kongsberg): US-series azimuth thrusters with power codes (e.g., US 305 at higher ratings) for OSVs and tugs.

V

Vacuum-pad alignment (laser): Laser alignment with vacuum-mounted targets on flanges and bearings.
Variable-pitch propeller: Synonym for CPP, with hydraulically variable blade pitch.
VEM electric motors: VEM Sachsenwerk supplies large medium-voltage motors used in podded and shaft-line electric propulsion.
Ventilated propeller: Propeller operating with air ingestion from the free surface, producing reduced and fluctuating thrust.
VFD propulsion drive: Variable-frequency drive feeding an electric propulsion motor, used in podded and conventional electric propulsion.
Vibration absorber (torsional): Geislinger or Hasse & Wrede torsional damper installed at the free end of the engine or on the shaft.
Vibration monitoring (shaft): Continuous measurement of lateral and torsional vibration on the shaft line, often via accelerometers and strain gauges.
Voith Inline Thruster (VIT): Voith permanent-magnet rim-drive thruster integrated in a duct.
Voith Linear Jet: Voith axial pump propulsor with stator vanes and a rim, used on workboats and OPVs.
Voith Water Tractor: Tug arrangement with two VSPs forward and a skeg aft, providing 360-degree thrust direction.
Voith-Schneider propeller (VSP): Cycloidal vertical-axis propeller.
Volvo Penta IPS: Forward-facing, twin contra-rotating tractor pod system for fast craft.
VR (variable rake) propeller: Generic term; omit unless verified maker product.
Vulkan coupling: Vulkan Kupplungs- und Getriebebau highly elastic torsional coupling used in medium-speed shaft lines.

W

Wageningen B-series: Open-water propeller series from MARIN.
Wageningen C-series: Controllable pitch propeller series tested at MARIN.
Wageningen Ka-Kd series: Ducted propeller series for nozzle 19A and related ducts, derived at MARIN.
Wake fraction (w): (V - VA)/V at propeller plane.
Wake peak: Region of low axial velocity behind a single-screw stern, typically at the 12 o'clock position.
Wake-equalizing duct (WED): Schneekluth duct (twin half-rings) fitted forward of the propeller to equalize the inflow.
Wartsila Aquarius (BWMS): Off-topic for shaft line; not used here.
Wartsila CP propeller: Wartsila controllable pitch propeller line, descended from Lips and KaMeWa.
Wartsila Energopac: Integrated propeller-rudder energy-saving package marketed by Wartsila.
Wartsila Modular Thruster (WST): Wartsila steerable thruster series (WST-E, WST-U) for offshore and merchant vessels.
Wartsila Steerprop: Steerprop (Finland), majority-owned by Wartsila, produces contra-rotating and conventional azimuth thrusters.
Wartsila Sternguard: Wartsila water-lubricated stern-tube bearing system, derived from Cedervall.
Water-lubricated stern tube: Stern-tube arrangement with seawater or fresh water as the bearing lubricant and polymer or composite staves; no aft oil seal required.
Wear-down gauge (poker gauge): Tool to measure aft stern-tube bearing wear-down through the rope guard, recorded at each survey.
WEBI duct (Wartsila Energy Boost Injector): Generic; omit if not a verified product name.
Whirling speed: Rotational speed at which a lateral natural frequency of the shaft line is excited, to be avoided in service.
White metal: Tin-based babbitt lining used in oil-lubricated stern-tube and intermediate bearings.
Wide chord tip propeller: Propeller with increased chord length near the tip for cavitation control on heavily loaded propellers.
Windmilling propeller: Free-spinning propeller driven by the water flow when the engine is stopped, relevant to twin-screw operations and CPP feathering.

X

X-bow stern interaction: Effect of Ulstein X-Bow hull form on aft flow; relevant where propeller wake is influenced by altered hull pressure distribution.

Y

Yard alignment record: Documented alignment sheet recording bearing offsets, gaps, sags, and jack-up reactions on first installation.
Yoke (CPP hub): Sliding yoke (crosshead) inside the CPP hub converting piston axial motion into blade pin rotation.

Z

Z-Drive: Azimuthing propulsion unit common on tugs.
Z-Peller (Niigata): Niigata Power Systems' Z-drive azimuth thruster product family.
ZF AT thruster: ZF azimuth thruster (AT series) for offshore and tug applications.
ZF marine gear: ZF Friedrichshafen reduction and reversing gearboxes (e.g., ZF 7000 series) used in workboat and naval shaft lines.
Zinc anode (propeller/shaft): Sacrificial anode mounted on the rudder, shaft, or hull to protect the propeller and shaft from galvanic corrosion.
Zinc dust paint (propeller temporary): Temporary surface coating applied during dry-dock to bronze propellers to mark erosion patterns (paint test).
Zwicker rudder: Generic; omit unless verifiable maker (no entry).