Terminology Flashcards
Rise of Floor
Rise of the floor (rise from the bottom or dead rise) is the upper slope of the ship’s bottom from the keel to the round of bilge. Rise of the floor is the vertical distance measures at the round of bilge between the baseline and a line drawn along the bottom. It assists in the removal of any fluids within the structure of the ship. Large modern ships appear to be very flat on their bottoms but in fact have a rise of floor.
Baseline
This is an imaginary fore and aft reference line drawn at the upper surface of the keel plate at amidships. It is used primarily in determining sizes and measurements according to the rules and regulation of classification societies. For example, vertical “molded” dimensions such as molded daft, molded depth, and the rise of floor are taken from this reference line.
Round of Bilge
The term round the bilge refers to the area of hull plating where the transition from the bottom to side shell occurs. The term “bilge” generally refers to an area in which any unwanted liquid will collect and from there can be pumped to an appropriate location. In some vessels this area is at the ship’s lower sides hence the term round of bilge strake reduces longitudinal bending stresses in this area. Ships that have a distinct sharp angle at the change of side to bottom plating are referred to as having a “hard chine”
Centreline (Midships)
A ship’s centreline is a vertical plane running for and aft along the length and through the centre of the ship form.
The hull form is symmetrical about this plane.
Design Water Line / Summer Load Line
Naval architects refer to this line as the design water line or just water line, in that this represents the deepest the ship is designed to be submerged (most cargo/mass)
From an operational perspective, Class Societies, Regulators, and Operators refer to this as a Summer Load Line. It represents the deepest the vessel may be legally submerged in seawater in the fairest seasonal sea conditions
Forward Perpendicular (FP)
This is an imaginary line drawn perpendicular to the Summer Load Line through the point where this summer load line intersects the forward section of the stem.
This perpendicular also serves as a reference point.
After Perpendicular (FP)
The aft perpendicular is used as one of the reference points for measurements along the length of the vessel. Generally it is an imaginary line drawn perpendicular to the summer load line at a point at the aft side of the rudder post.
Some ships also do not have a rudder stock (i.e azimuth drive propulsion). In these cases the International Load Line Convention defines the aft perpendicular as a point measured from the forward side of the stem and equal to 96% of the length of the waterline while flowing at 85% least molded depth.
Length Measurements
Amidships is a point found midway between the forward and after perpendiculars. It is used as a reference point for stability calculations as well as to describe the positioning of structures on a vessel. A symbol denoting this point is normally used.
Sheer
Sheer is the longitudinal curvature of the decks from bow to stern. The lowest part of the curve is approximately located at amidships but will vary depending on the type of ship.
It is measured as the vertical differences between the heights of the deck amidship at the ship’s sides, and at the bow and stern (thus giving forward sheer and an after sheer) The forward sheer is about two thirds of total sheer with the remaining one third being after sheer.
The purpose of sheer is to help reduce the amount of water being shipping over the bow or stern. It also provides a small degree of extra reserve buoyancy in these areas in the event of a forward or after trim. Most ships and fitter with a forecastle thus reducing the need for sheer.
Extreme and Moulded Measurements
Breadth ~ width how far does everything stretch.
Moulded ~ interior width , measures the hull
Displacement Light
Displacement is the mass of the water displaced by the hull. Light displacement is the mass of the ship expressed in tonnes and includes all machinery, equipment, hull and operational fluids for the machinery (i.e oil in sumps, water in boilers)
Displacement Loaded
Loaded displacement (maximum displacement) is the mass of the ship in its greatest loaded condition measure in tonnes. This includes cargo, fuel, water and provisions, crew, and personal effects.
Deadweight
Deadweight (Dwt)
Dead weight is the mass that a ship can carry expressed in tonnes. It is equal to the difference between light and loaded displacements.
Normally it is abbreviated as DWT but sometimes as DWAT (deadweight all told) Deadweight included cargo, fuel oil, lubricating oil, fresh water, ballast water, stores, passengers and baggage, crew and affects.
Sometimes deadweight is used to express the cargo-carrying capacity of a ship. At that time, is abbreviated as DWCC (deadweight cargo capacity or deadweight carrying capacity)
Tonnage
Ships are described in term of their internal cubic capacity with 1 tonne being expressed as 100 ft3 or 2.83 m3
Gross tonnage (gross registered tonnage) GT or GRT is the total of all enclosed spaces within a ship.
Net tonnage (net registered tonnage) NT or NRT is the total of all the enclosed spaces on board a ship that are available for cargo. These values bare calculated by the use of suitable formulae with corrections being made for various exempted spaces.
Flare
Flare is the outward curvature of the bow shape from the water line to the upper edge of the plating.
This shape keeps a drier deck during heavy seas as the water tends to be thrown outward from the hull.
