Ship Construction Terminology Flashcards
Measurements
Measurements Continued
Summer Load Line
The measured load line depicting the vessels assigned freeboard
Define Aft and Fwd Perpendiculars
AP: Vertical Line Perpendicular to the Base line where the summer load line crosses the stern
Usually passes through the Rudder Stock on a conventional Ship
FP
Vertical line perpendicular to the base line where the Summer Load Line crosses the Stem
-Length between perpendicular
-Amidships
The length of the measured value between the forward and aft perpendiculars
Amidships, Mid point along LBP
Length Overall
Extreme length of the vessel
Length on the waterline
Length at waterline measured at any given draught
-Sheer
-Depth
Sheer: Longditudinal curvature of the deck, adding buoyancy to the ends of the vessel, and gives protection for the crew in a seaway
Depth: The vertical distance between the baseline and the freeboard deck at amidships
Flare
The curvature of the bow plating. Allows anchors to drop clear and increases the buoyancy of the bows in a seaway
Camber
Transverse curvature of the deck, allowing the deck to shed water
Light displacement
The mass of a ship when complete and ready for sea, but with no passengers, cargo, fuel or stores. an Empty ship
Load/Summer Displacement
Mass of the vessel when fully loaded, floating at her assigned freeboard
Displacement
Mass of the vessel floating at any given draught between light displacement and summer draught marks
Δ = Underwater Volume (V) x Relative Density (RD) of the water.
Deadweight
Difference between lightship displacement and Displacement at any given time/Draught
Summer deadweight
Difference between lightship displacement and Summer displacement at the assigned freeboard
Summerdisplacement - Light displacement
Gross Tonnage
Internal volume less certain exemptions, calculated at a rate of 2.83 m cuber per tonne
Net tonnage
Obtained by deducting the non-freight spaces from the GT (accomodation etc)
Freeboard Deck
The uppermost continuous watertight deck having permanent means for closing all openings to maintain watertight integrity. Below which all Openings in the vessels side have permanent means for watertight closure
Superstructure
Parts of a ship, apart from its Masts and rigging, Built above the hull and main deck
Superstructure Deck
Deck forming an upper boundary around the superstructure
Assigned freeboard
The vertical distance amidships between the upper edge of the freeboard deck, to the upper edge of the Summer Load Line
Beam
The greatest measured breadth measured to the outside of the shell plating
Draught/Draft
The vertical distance between the baseline and the current waterline
Reserve Bouyancy
The volume of the enclosed spaces between the waterline and freeboard deck. Expressed as a % of the total enclosed volume of the Ship.
This should be enough that if the largest watertight compartment is holed, the vessel will stay afloat
Tonnes per Centimetre Immersion
The mass required to load/discharge in order to change the mean draught by 1cm
Simple Beam
Simple Beam
When a uniform beam is sagged (its centre droops) the upper layer is compressed and the
lower experiences tension. Between the two there will be neither tension nor compression, the
neutral axis.
Motions
What reduces Longitudinal stresses?
Centre Girders
Side Girders
Longitudinal Girders
Stringers
Hull and Shell Plating
What reduces Transverse Stress (racking)
Transverse Bulkheads
Web frames
Beams
Beam Knees
Transverse stiffener
Similar to transverse frames but these are smaller and not full height
Longitudinal stiffener
Run longitudinally parallel to the centre girder, resist hogging and sagging
Vertical Stiffeners
These run vertically perpendicular to the waterline, adding strength to girders if required
Stringer
Horizontal stiffeners running parallel to the waterline to help resist forces such as panting
Continuous Centre Girder
Large steel one section girder running longitudinally along the ship, and resting on the Keel Plate. This helps to resist hogging and sagging by giving longitudinal strength to the ship.
Plate floor
Made up of Vertical/horizontal plates running across the ship
Gives transverse strength
Supports the bottom plating and transfers the weight of the surrounding ship into the water downwards
Can have lightening holes, manholes and limber holes for drainage
Hull / Shell Plating
The outer layer, skin of the ship. Designed to keep water out and support the structure.
Upper and lower ‘strakes’ are thicker to give added strength and resist hogging/sagging
Transverse Frame
The ‘ribs’ of the ship giving support to the plating, deck and deck beams, As well as transferring the load from the deck down
Beam Knee
Supports the join between the deck beam and the transverse frame. Resists racking and helps to transfer load from the deck into the frames
Deck girder
Supports the deck and secures the deck beams adding longitudinal strength and helping to resist hogging and sagging
Deck Beam
Supports the deck and transfers load from the deck to the transverse frames. Adds transverse strength to help to resist Racking
Pillar
Supports the deck beam, transfers load to the plate floor
Side Stringer
Horizontal longitudinal girder giving support to the frames and adding longitudinal strength to the structure
Hogging
A vessel is said to be hogging when she is supported amidships, with unsupported bows and stern, causing them to droop
Sagging
A vessel is said to be sagging when she is supported on the bow and stern by two crests of waves, and unsupported amidships, causing the bow and stern to bend upwards
Racking Stress
When a vessel rolls in a seaway, the deck tends to move laterally relative to the bottom structure. This also tends to move the shell vertically on one side relative to the other. A stiff ship is prone to racking
Local Stresses of:
Sheering stress
Point loading
The force exerted on a ship structure when two external parallel forces act in opposite directions to each other, to break it or shear it apart.
Point loading, caused by large amounts of force being exerted in place. Often caused due to incorrect loading arrangements, the mast of a sailing vessel etc
Panting
The in and out movement of the shell plating due to changes in pressure, experienced most heavily in the bows of the vessel
Local Force of: Pounding
Occurs in the bottom shell forward, when the vessel is driven head onto rough seas.
It creates a loud bang followed by a shudder vibration as the stresses transfer back through the hull
Reducing pounding
- Alter Course (do not drive directly into waves).
- Reduce Speed (do not fly into waves).
- Increase Scantlings (structural elements, like a honeycomb).
- Thicken Shell Plating.
- Plate Floors.
Define Fresh Water Allowance (FWA)
FWA = Displacement/4 x TPC (SW)
The amount in mm a ship may legally submerse the appropriate salt water mark when in Fresh water.
The difference in draught when a vessel moves from Salt water to Fresh Water
