Ship Hull and Tank Definitions

Hull Form Definitions

• Sheer is the upward curve of a ship's deck from the bow to the stern, providing buoyancy and enhancing seaworthiness.

• Stem Rake is the angle of the stem line, extending from the bow downwards, relative to the vertical.

• Keel Rake is the angle of the keel line, connecting the bottom of the hull, relative to the horizontal.

• Parallel Middle Body refers to the central portion of a ship with a consistent cross-section, minimizing resistance during sailing.

• Entrance is the section of the ship's hull forward of the parallel middle body, designed for efficient water penetration.

• Run is the section of the ship's hull aft of the parallel middle body, designed for effective propulsion.

Ship Tank Types

• Double Bottom Tanks are positioned beneath the ship's hull, formed by additional plating, used for ballast or fuel storage.

• Peak Tanks are located at the vessel's extremities, forward (forepeak) and aft (afterpeak), primarily used for ballast water.

Double Bottom Structure

• Watertight Center Girder divides the double bottom space into port and starboard sections, ensuring watertight integrity.

• Side Girders run along the sides, not watertight but featuring lightening holes for structural optimization.

• Watertight Floor is a solid plate, spanning the entire tank, ensuring watertightness between compartments.

• Plate/Solid Floor is similar to the watertight floor but with openings for ventilation and drainage.

• Bracket/Open Floor is a supporting structure between plate floors using bar sections and flanged brackets for tank top support.

Sounding

• Sounding determines the fluid level within a tank by using a sounding tape.

• The final sounding value represents the total fluid quantity in the tank.

• The initial sounding involves measuring the fluid depth from the surface to the bottom of the tank using a sounding tape.

Sounding Pipes

• Vertical pipes running from the deck down to the bottom of the tank, allowing for sounding checks.

• Fitted with a cap for closure, preventing flooding during inclement weather.

• They are connected to automatic closing valves to prevent oil vapor leakage in machinery spaces.

Air Pipes

• Air pipes are situated on tank ceilings allowing free airflow, preventing pressure or vacuum build-up.

• Fitted with vents to prevent flooding during bad weather.

• Also used in void spaces, cofferdam spaces, and cargo holds, serving as automatic ventilators.

Ventilators

• Ventilators provide fresh air circulation for compartments for safety and hygiene.

Load Line Marks

• Deck Line - Horizontal line 300mm by 25mm, aids in determining the vessel's freeboard.

• Load Line Disc - 300mm diameter and 25mm thick disc, with a horizontal line marking the "Summer saltwater line" or Plimsoll Line.

• Load Lines - Horizontal lines extending from a vertical line, indicating maximum allowed submergence based on season and location.

• Freeboard - The distance between the waterline and the upper edge of the deck plating, indicating safe load limits.

• Summer (S) - The primary freeboard line, corresponding to the Plimsoll Line.

• Tropical (T) - Marked 1/48th of the summer draft above the Summer load line, for low-risk tropical voyages.

• Winter (W) - Marked 1/48th of the summer draft below the Summer load line, for winter voyages.

• Winter North Atlantic (WNA) - Marked 50mm below the Winter load line, for voyages in the North Atlantic during winter.

• Fresh Water (F) - Marks the summer freshwater load line, compensating for lower water density.

• Tropical Fresh Water (TF) - The freshwater load line in tropical regions, marked above the T.

Seasonal Zones

• Summer - Voyages with less than 10% winds of force 8 Beaufort or higher.

• Tropical - Voyages with less than 1% winds of force 8 Beaufort or higher and less than one tropical storm in a decade within a 5-degree square area.

Ship Dimensions

• Length Overall (LOA) - Extreme length from the most forward to the most aft point, measured along the design waterline.

• Length Between Perpendiculars (LBP) - Distance measured along the summer load waterline, between the forward and aft perpendicular lines.

• Extreme Breadth - The maximum breadth across the ship's widest point.

• Moulded Beam or breadth - Measured between the inner edges of the ship's hull plating.

• Extreme Depth - The vertical distance from the upper deck to the bottom of the keel.

• Moulded Depth - Measured from the top of keel to the upper deck, excluding any deck fittings or projections.

• Forward Perpendicular (FP) - A vertical line at the intersection of the design load waterline and the forward face of the ship's stem.

• Aft Perpendicular (AP) - A vertical line at the intersection of the summer load waterline and the after side of the rudder post.

• Amidship - The middle point of the ship, longitudinally or laterally.

• Draft - The vertical distance between the waterline and the bottom of the ship's hull (keel).

• Freeboard - The vertical distance measured from the waterline to the upper edge of the deck plating at the ship's side.

This quiz covers essential definitions related to ship hull forms and tank types. You'll explore terms like sheer, stem rake, and double bottom tanks, which are fundamental for understanding naval architecture. Test your knowledge and enhance your comprehension of maritime concepts.