DICTIONARY OF

Profile Draughts 263 Propeller
Profile Draughts. Two sheer plans on principle of cargo plans. One gives layout of ship; the
other giving layout of fittings in ship.
Pro Forma Policy. Temporary and unsigned policy issued to an insurer pending the
preparation and signing of the actual policy.
Progressive Wave. Elevation of water, with its accompanying depression, that moves
laterally along surface of sea. Considered in tidal investigations.
Projections. Attempts to delineate some part of curved surface of Earth on the flat surface of
a map or chart. It is impossible to do this with accuracy. In the projections used by seamen
the distortions are either negligible in practice or are of a known nature and value and can,
therefore, be allowed for. The different projections are treated under their separate names.
Prolate Spheroid. Spheroid generated by semi-rotation of an ellipse around its major axis.
Sometimes applied to a spheroid that rotates on its major axis.
Prolongation Clause. Inserted in a charter party to give charterers option of continuing a
charter beyond a given date. States the conditions under which this can be done.
Prolonged Blast. Blast, of 4 to 6 seconds duration, on a whistle, foghorn, or siren.
Promenade Deck. One of the decks of a passenger steamer. Usually more or less open and
free from obstructions.
Promissory Note. Written and stamped undertaking to pay a specified sum of money on or
before a specified date.
Proof Load. Excessive load put on an item under test. May vary between 10% and 100%
more than the load that the item is intended to take.
Proof Strain. Excessive strain put on an item under test. Always exceeds strain that the item
is intended to take.
Proof Stress. Value used to indicate strength of metal when it is difficult to determine yield
point. Metal is stretched and its elongation under the stated stress is expressed as a
percentage, the value of the stress being stated.
Proof Timber. Vertical straight line, representing a timber, drawn on a sheer draught for
checking fairness of ship's form.
Propeller. Instrument by which a vessel is propelled. Attached to after end of a shaft that is
connected to engine. Usually has three or four blades, each being part of a screw thread, and
is keyed and secured to after end of tailshaft.
Controlled Pitch Propeller. The blades of the propeller can be altered in position to give
ahead, neutral, or astern drive, the engine turning in a constant direction.
Ducted, or Shrouded, Propeller. A propeller rotating within an open-ended cylinder
sometimes called a 'Kurt Nozzle". The duct increases significantly the bollard pull of a tug.
If the duct and propeller is turned horizontally great manoeuvrability is achieved.