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Encyclopedia of Marine Technology


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Product tanker; Tank cleaning

Tank cleaning may be required for one or more of the following reasons: 1. To carry clean ballast. 2. To gas free tanks for internal inspections, repairs or prior to entering dry dock.

Production facilities

The processing, safety and control systems, utility and auxiliary equipment, for producing hydrocarbon liquid and gas mixtures from completed wells or other sources.

Production tubing

A pipe used in wells to conduct fluid from the producing formation into the Christmas tree. Unlike the casing, the tubing is designed to be replaced during the life of the well, if required.


A side elevation of a ship form.

Progressive collapse

The gradual collapse of the hull girder, involving the spread of elasto-plastic buckling throughout a transverse section, following which the vessel is no longer capable of sustaining any longitudinal bending loads.

Projected area of a propeller

This is the sum of the area bounded by the outline of the blades when projected onto a plane perpendicular to the axis of the screw.

Prompt and thorough repair

Permanent repair completed at the time of the survey to the satisfaction of the surveyor, therein removing the need for imposition of any associated condition of class.

PROPAC (propulsion package)

An integrated mechanical propulsion system developed by Wärtsilä as a single supplier with commitment to lifetime support.

Propeller boss cap fins (PBCF)


Propeller clearances

The distance from the propeller to the hull has a linear influence on the pressure impulses. A reduction of this clearance by 50% doubles the pressure impulses. To account for the ice class it is necessary to increase the thickness of blade sections.

Propeller diameter

The largest possible propeller diameter is preferred in order to obtain the highest possible propulsive efficiency.

Propeller excitation forces

The propeller is a potential source of noise and vibrations in a ship. The vibration of a propeller are strongly related to the variation in inflow velocity (wake-field), the clearance from propeller tip to hull surface and blade geometry.

Propeller hub (of CP propeller)

The hub is bolted to the flanged end of the tailshaft. Without ice class, the hub diameter/propeller diameter ratio varies between 0.20 and 0.25.

Propeller nozzle

A circular casing enclosing the propeller. The propeller operates with a small gap between blade tips and the nozzle internal wall, roughly at the narrowest point. The nozzle ring has a cross-section shaped like a hydrofoil.

Propeller pitch

The distance that a propeller theoretically (i.e. without slip) advances during one revolution.

Propeller rake

It is the distance at the blade tip between the generating line and the line perpendicular to the propeller axis that meets the generating line at the propeller axis.

Propeller shaft coupling flange

For connecting the propeller shaft with the intermediate shaft, a hydraulic coupling flange is used.

Propeller shaft, tail shaft

The aftermost section of the propulsion shafting in the stern tube in single screw ships and in the struts of multiple screw ships to which the propeller is fitted.

Propeller skew angle

Skew angle of a propeller is the angle measured from ray “A” passing through the tip of the blade at mid-chord line to ray “B” tangent to the mid-chord line on the projected blade outline.

Propeller surface finish

A propeller surface finish has big effect on fuel consumption. A surface finish of 70 microRa will add over 4.5 per cent to the fuel consumption bill compared with one of 10 microRa.

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