Key Naval Technology Terms and Definitions

Seat: The difference between forward and aft draft (CPP - CPR). An aproppriate seat is a positive seat.

Offset: The maximum volume of water displaced, equivalent to the weight of the ship with its load.

Tonnage: A measure of a ship's volume, recorded in Morson tons. 1 Morson ton = 2.83m³ = 100 cubic feet.

Scuppers: Holes in the shell plating on the deck, allowing water to drain overboard.

Sea Chests/Sea Suction: Cooling water inlet valves.

Sternpost Horn: The tube at the forward face of a bow thruster is called the horn.

Portholes: Side openings for light and ventilation.

Hatches: Internal access openings on the ship's deck.

Skylights: Openings on the deck to provide light and ventilation.

Bollard Bitt: A piece of iron or steel used for securing ropes.

Barbotin: Part of the windlass or anchor-weighing machine.

Rudder and Propeller Terminology

Rudder Offset:

• Regular or Flat: A flat surface that rotates about a vertical axis at the aft of the ship, used to maintain or change course.
• Compensated: Requires half the effort to move compared to a regular rudder.

Propeller: Consists of blades attached to a shaft that rotates in a helical motion, propelling the ship.

Pitch: The theoretical distance a propeller would advance in one revolution in a solid medium. Constant pitch is proportional to the angle of rotation; variable pitch is not.

• Right-handed (Dextrorotatory): When viewed from aft, rotates clockwise when going ahead.
• Left-handed (Levorotatory): Rotates counterclockwise when viewed from aft.

Cavitation: The formation of gaps or cavities on the blades under specific conditions, characterized by increased speed and foaming at the stern. It is avoided by reducing speed gradually.

Controllable Pitch Propeller: Features a mechanism that rotates the blades around a vertical axis, allowing for adjustment of the pitch in either direction or neutralizing it. The propeller shaft always rotates in the same direction.

• Propeller Diameter and Drag: Larger diameter, smaller pitch.
• Propeller Diameter and Speed: Smaller diameter, larger pitch.

Folding Propeller: Blades can fold in the same direction as the axis, used in sailboats to avoid friction.

Double Propeller: Two propellers that rotate in opposite directions, creating greater momentum and utilizing the water cylinder's power more efficiently (up to 40% improvement) by reducing turbulence. Backspacing is the difference between the theoretical advance (pitch) and the actual advance in a given time.

Mooring Elements

• Breast Line: Mooring line led nearly perpendicular to the ship.
• Seno: The curvature of a mooring line.
• Eye Splice: A loop used to secure a mooring line.
• Standing Part: The longer part of a rope.
• Bitts: A strong point on a ship for securing lines.
• Bollard/Noray: A post, often with a curved upper extremity, placed on a dock or cliff for mooring.
• Righting Moment: The tendency of a ship to return to an upright position after heeling.
• Take in: To haul in ropes.
• Check: Keep the mooring lines at equal tension.
• Ease: To gradually slacken a line.
• Lower: To lower something that is suspended.
• Let Go: To release something from where it was secured.