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
Flare
Outward curvature of the bow to keep deck dry
Wider = drier but need more energy to advance through water
Narrower = less energy to go faster, but less cargo space
Bows
- Bulbous (curved)
- Plumb (flat)
Sterns
- Transom (easier to construct)
- Cruiser (rounded)
Sternframe
Cast, forged or fabricated section used to support the rudder, propeller shaft and propeller.
Rake
Angle of inclination from vertical (funnel, mast) or horizontal (bow, keel)
Double bottoms
- Provides space between bottom hull plating & interior of the ship
- Height determined by classification society rules
- Provides a degree of safety against flooding in the even to hull damage
- Significant contribution to longitudinal and transverse strength of ship
- Convenient storage area
- Helps with stability
- Tank top acts as platform for machinery & cargo
Poop deck
Aft-most deck above freeboard deck located right behind the main bridge superstructure
Freeboard deck
AKA Main Deck
AKA Strength Deck
AKA Bulkhead Deck
Uppermost watertight deck
Deck house
Structure on freeboard deck to serve as small storage or pump rooms.
Located near gangway
Superstructure
AKA Deck erection
AKA Deck structure
All structures above freeboard with width within 4% of moulded breadth of vessel
Will house emergency equipment like generator and battery banks
Bridge Superstructure
May be aft (cargo ships) or the majority of the length (cruise ships)
Includes accommodations, nagivation, communication, recreation
Forecastle
Raised area in the bow, used for storage
Chain locker
Area located under the windlass for storage of the anchor cable.
Ships generally have 2 anchors with a single locker whose space is divided in half
Accessible through the forecastle
Bulkheads
Vertical partition, can be longitudinal or transverse
Used for strength, compartmentalization, protection against spread of fire/smoke & flooding
Collision bulkhead
Forward location, heavy construction. Made to withstand impact damage & hydrostatic pressure of flooding
Aft peak bulkhead
Rear-most transverse watertight bulkhead.
Generally serves as after-machinery space bulkhead to protect machinery from rear damage
Deep tanks
Extend across full width of ship, deep in the vertical direction. Often used for fuel or water storage; can be used to trim/draft vessel
Topside tanks
Used to keep vessel trim/list while loading & unloading
Lower hopper tanks
Additional ballast space, slope cargo towards center for ease of collection
Side tanks
Used for container ships & tankers when vessel isn’t carrying cargo
Forepeak and aftpeak tanks
Used for precision trimming operations, irregular shapes
Forepeak: below chain locker
Concern: corrosion is not coated properly
Cofferdams
Additional protection between 2 spaces/tanks.
Void space to note any leakage from either tank.
Failsafe mechanism
Auxiliary machinery
Everything that isn’t the main engine
Machinery space
Generally completely aft to shorten length of propeller drive shaft
Funnel
Need way to vent out exhaust as high as possible and efficiently
Also provides intake for ventilation
