Module 1 : Terminology Flashcards
What are the directions on a vessel?
Longitudinal direction: foward (front, towards the bow) & aft/astern (back, towards the stern).
Transverse direction: port (left) & starboard (right)
What are the reference planes on a vessel?
Centreline plane: longitudinal & vertical (hull is symmetric about this plane)
Waterline plane: longitudinal & transverse (at even trim, parallel to the keel)
Midship plane (or amidships plane): transverse & vertical at midpoint between forward and aft perpendiculars
What are the reference lengths on a vessel?
- Length overall (LOA)
- Length between perpendiculars (LBP) -> forward perpendicular is taken at the intersection of summer load line and bow; aft perpendicular is taken from the rudder post. This measurement is used for stability and displacement calculations
Length at waterline (LWL): depends on ship loading
Sheers
Purpose: reduce amount of water being shipped onto the deck & provide small amount of extra reserve buoyance
Sheer forward: measured vertically from the main deck to the peak of the tip of the bow. Approx 2/3 of total sheer.
Sheer aft: measured vertically from the main deck to the peak of the stern. Approx 1/3 of total sheer.
Sections of the vessel
Parallel mid-body: hull area and shape remain constant.
Forward of this: entrance (a measure of the bluntness of the bow - hydrodynamic flow)
Aft of this: run (the flow of water over the propellers - propulsion & turbulence)
Beams
B. Ext : outside of shell plate
B. = B. Mld. : inside of shell plate
Camber : vertical distance between the curve of the deck and the horizontal line from edge of deck, measured at centerline (removes water from deck)
Tumblehome: horizontal distance between the actual and theoretical side plate (reduces roll)
Round of the bilge: reduced longitudinal bending stresses, easier to plate
Rise of floor: vertical distance between flat of keel and angle of bilge (forces water to pool towards the keel)
Draft (d)
d Ext. : summer load line to lowest point of hull
d Mld. : summer load line to baseline at amidship
df: forward draft
da: aft draft
mean draft : df+da/2
Depth (D)
Moulded: from baseline to heel of deck beam
Depth = freeboard + draft
Freeboard
Purpose: vessel safety, reserve buoyance
Reserve buoyance: volume of watertight hull between waterline and freeboard deck, can include deckhouse and superstructure
Draft marks
At forward and aft, but long vessels will also have them at midship.
Metric: numbers (even) are 10 cm tall and placed 10 cm apart
Imperial: numbers (even) are 6” tall and places 6” apart
Hull markings
Load lines
Ship registration & flag state: process whereby ship is documented & given a nationality, is proof of ownership. Ship is subject to the law of its flat state. Could be actual home country or registration of convenience
IMO registration: unique 7 digit #, required on passenger ships over 100 gross tonnes and cargo ships over 300 gross tonnes.
Standard displacement
Volume of underwater hull (weight of water displaced) MINUS fuel & potable water
Displacement light
Mass of ship PLUS machinery, equipment, hull, operational fluids for machinery
Displacement loaded
Mass of ship PLUS cargo, fuel, crew, provisions.
Maximum displacement
Deadweight
Displacement loaded - displacement light
Important calculation for cargo ships
Lightweight
Actual weight of ship
Gross tonnage
Entire internal volume of a ship, total volume of all enclosed spaces
Compensated gross tonnage
Includes factor for ship size
Net tonnage
Around 75% of gross tonnage
Earning capacity/ useful space on ship.
Many factors: volume of cargo space, moulded depth, moulded draft, # of passengers
Ship motions (linear)
Longitudinal: surge
Transverse: sway
Vertical: heave
Ship motions (rotation)
Longitudinal: Roll
Transverse: pitch
Vertical: yaw
Ship material
Be able to recognize flat, angle, round, I beam, half round, T bar, offset bulb
Ship framing
Longitudinal (vessels over 120m) gives more strength
Transverse (vessels under 120m)
Stem
Forward-most part of bow, has an angle
