Ship construction Flashcards
FORWARD PERPENDICULAR
(FP)
Vertical line perpendicular to the base line where the summer load line crosses the stem
AFT PERPENDICULAR
(AP)
Vertical line perpendicular to the base line where the summer load line crosses the stern
LENGTH OVERALL
(LOA)
The extreme length of the vessel
LENGTH ON LOAD WATERLINE
(LWL)
The length measured along the current waterline
AMIDSHIPS
The mid - point of the LBP
BEAM
The greatest breadth measured to the outside shell plating.
LENGTH BETWEEN PERPENDICULARS (LBP)
The length of the vessel measured between the forward and aft perpendiculars
DEPTH
The vertical distance between the baseline and the freeboard deck at amidships
DRAUGHT / DRAFT
The vertical distance between the baseline and your current waterline
FREEBOARD
The vertical distance between the uppermost continuous watertight deck (freeboard deck) and the waterline at amidships
ASSIGNED FREEBOARD
The vertical distance between the freeboard deck and the SLL (summer load line) at amidships
REVERSE BUOYANCY
Volume of the enclosed watertight spaces between the load line and the free board deck.
The reverse buoyancy must prevent the deck line submerging when the largest watertight compartment is bilged
CAMBER
Transverse curvature of the deck, helping to shed water from the deck.
SHEER
Longitudinal curvature of deck, adding buoyancy to the ends of the vessel.
FLARE
outward curvature of the bow. Increases buoyancy and keeps the heads dry.
CENTRE LINE
The middle line of the ship extending from the stem to stern at any level.
TRANSVERSE CROSS SECTION
A drawing showing standard cross sections of the hull or near amidships, and showing the scantlings of the main structural members.
SCANTLINGS
The size/strength of structural elements - frames girders, stiffeners, stringers and plates
TONNE
A measurement of weight
1tn = 1000kg
LIGHT DISPLACMENT
Mass of the vessel when complete and ready for sea but with no passengers, stores , fuel or cargo on board. An empty ship
DISPLACMENT
Displacement = underwater volume x relative density of the water
Mass of the vessel floating at any draft between light displacement and summer draft marks.
LOAD DISPLACMENT
Mass of the vessel fully loaded with cargo, stores, etc floating at her assigned freeboard
DEADWEIGHT
Difference between lightship displacement and displacement at any given draft
LOAD / SUMMER DEADWEIGHT
Difference between lightship and summer displacements at the assigned freeboard.
Load displacement - light displacement.
GROSS TONAGE
Internal volume of the ship
NET TONNAGE
Obtained by deducting the non freight spaces (accommodation etc) from the GT
TONNES PER CENTIMETER IMMERSION (TPC)
The mass required to load or discharge in order to change the mean draft by 1cm
LIST THE SIX DIRECTIONS OF MOVEMENT A VESSEL MAY EXPERIENCE
- Yaw
- Sway
- Roll
- Heave
- Pitch
- Surge
SAGGING
When the ends are supported by wave crests and the midships section is unsupported causing the bow and stern to bend upwards.
compression
Neutral Axis
tensile stress
HOGGING
is supported amidships by a wave crest and the ends are unsupported so that the bow and stern droop.
tensile stress
Neutral Axis
compression
RACKING STRESSES
When a ship is rolling the deck tends to move laterally relative to the bottom structure. This also tends to move the shell vertically on one side to the other. This deformation is called racking.
HOW TO REDUCE RACKING
Transverse bulkheads
Web frames
Beams and Beam Knees
PANTING
Panting is the in and out movement of the shell plating due to varying pressure changes.
most common at bow
REDUCE PANTING
- Panting stringers
- Panting Beam
- Transverse Bulk heads
- Thicken shell plate
- Deepen Floor
POUNDING
Is the vertical slamming of the forefoot of the vessel onto the trough of a wave being caused by a combination of pitching and heaving.
Produces large impulsive forces on bottom plating
REDUCING POUNDING
- Alter course
- Reduce speed
- Increase scantlings
- Thicken shell plating
- Plate floors
DIFFERENT STRESSES ON THE VESSEL
Local loading stress-
Can be caused by heavy weights concentrated on small areas
(under main engines)
(Longitudinal stress carrying members of the structure meet transverse members)
Poor design
(A sharp angle cut in a plate produces a discontinuity) - When a Tensile stress is applied, the stress is concentrated at the angle
Vibration
Causes cyclic forces in steel usually resulting in tensile stresses.
TRANSVERSE CONSTRUCTION
- Used by cargo ships
- Main strength members transverse frames separated by beams
- Structure subject to racking.
-racking reduced by brackets or beam knees. - Ship divided by transverse bulkheads to act as water tight divisions
TENSION / COMPRESSION / NEUTRAL AXIS
When a uniform beam is sagged (its centre droops) the upper layer is compressed and the lower experience tension. between the two there is neither compression or tension, the Neutral axis.
HULL / SHELL PLATING
- Water tight skin of the ship
- Provides longitudinal strength
- Support for the transverse frames.
DECK PLATING
- Plating keeps water out
- supplies longitudinal strength
- support for the deck super structure.
TRANSVERSE CROSS SECTION - CENTER GIRDER
large steel section girder running the length of the ship. it gives longitudinal strength to the ship helps to resist hogging and sagging.
TRANSVERSE CROSS SECTION - PLATE FLOOR
- Vertical plates running along the ship
- Gives transverse strength to the structure
TRANSVERSE CROSS SECTION - HULL / SHELL PLATING
- water tight skin of the ship
- designed to keep water out
- resistant to hogging and sagging
- supports the structure
TRANSVERSE CROSS SECTION - TRANSVERSE FRAME
- Ribs of the ship
- resistance against racking
- supports the plating , deck and beams
TRANSVERSE CROSS SECTION - BEAM KNEE
- Unites the beam and the frame
- Resists racking
- Helps transfer load from the deck to the frames
TRANSVERSE CROSS SECTION - DECK GIRDER
- supports the deck
- adds longitudinal strength
- resists hogging and sagging
TRANSVERSE CROSS SECTION - DECK BEAM
- Supports the deck
- Adds transverse strength to resist racking
- Transfers loads from deck to frames
TRANSVERSE CROSS SECTION - PILLAR
- support the deck beam
- transfers weight to the plate floor.
TRANSVERSE CROSS SECTION - STRINGER
- Horizontal longitudinal girder
- Gives support to frames
- resists hogging and sagging
TRANSVERSE CROSS SECTION - CONTINOUS CENTRE GIRDER
- runs the length of the ship
- Gives longitudinal strength to the ship
- Reduces effects of hogging and sagging
STEEL - ADVANTAGES
- cheap
- easy to work with
- relatively strong
- recyclable
- widely available
STEEL - DISADVANTAGES
- Corrosion,
- relatively heavy 3x heavier than aluminium
- conducts heat / needs insulation
- needs regular maintenance
ALUMINUM - ADVANTAGES
- light
- does not rust
- easy to work
- less maintenance require
- Good radar reflector
ALUMINIUM - DISADVANTAGES
- expensive
- poor fire resistance
- corrodes with other metals
- requires specialist welding
FIBRE RIENFORCED PLASTIC (FRP) - ADVANTAGES
- corrosion free
- light
- comparatively easy to repair
- cheap especially if mass produced
FIBRE RIENFORCED PLASTIC (FRP) -
DISADVANTAGES
- Comparatively easily damaged
- toxic fumes once burned
- skilled construction required
- Osmosis
WOOD ADVANTAGES
- strong
- corrosion resistance
- buoyant
- aesthetically pleasing
WOOD - DISADVANTAGES
- expensive
- rots
- burns
- marine boar
GENERAL ARRANGEMENT PLAN
- boat name and yard number
- profile view
- deck plan, deck on deck
- general layout of cabins and furniture
- scale, frames and general dimensions
- main particulars, length , breadth , draught
- stairways ,escapes, bulkheads ,engine layout, escape hatches
FIRE, LIFE SAVING APPLIANCE AND BILGE PUMPING PLANS
Must be displayed in the following locations -
- bridge
- engine control room
- in the crew accommodation and mess rooms
it is a GA plan with all fire fighting equipment marked on it.
OXIDATION IN STEEL
- Caused when the oxygen in the atmosphere combines with the metal and forms iron oxide.
- The oxide film is not firmly attached to the parent plate and thus permits further oxidation to occur
OSMOSIS
FRP construction can be damaged by Osmosis. This is seen by cracking or blistering of the surface.
Gel coat damage allows water to come into direct contact with resins which are porous and allow resins to be sucked in.
ELECTRO CHEMICAL (GALVANIC) CORROSION
- The galvanic action is a form electrolysis whereby different metals will react with one another to form an electric cell when placed in suitable medium.
- in this case less noble metal is the aluminium which will give up its ions become eaten away.
- the Aluminium is known as the anode whilst the steal becomes the cathode. The process is speeded up due to the efficient salt water electrolyte
SACRIFICIAL ANNODES
By providing a piece of material lower down the anodic index (usually zinc ) it will corrode in preference to the vital parts of the vessel. These are known as sacrificial anodes.
They are attached to the hull near the propeller and inside tanks.
IMPRESSED CURRENT CATHODIC PROTECTION (ICCP)
- If the galvanic current can be suppressed, the corrosion can be stopped.
- By passing a current of the same strength through the electrolyte but in the opposite direction the galvanic action is cancelled out and no corrosion occurs.
- comprises of a rectifier, controller and computer system.
SUMMARIZE THE LOYDS NOTATION BELOW
X100A1
SSC
G6
UMS
X - ( Maltese cross) New ship built under supervision of a society surveyor
100 - considered suitable for seagoing service
1 - anchor mooring equipment comply with Lloyds class rules
SSC - special service craft
G6 - geographical restrictions
UMS - unmanned machinery spaces
IACS
international association of classification societies
MAIN FUNCTIONS OF CLASSIFICATION SOCIETIES
- satisfactory standards of strength, stability and safety
- decide how ships should be built
- surveying
THE ROLE OF CLASSIFICATION SOCIETIES
- construction for all types of vessels
- material spec
- approve LSA and FFE
FRESH WATER ALLOWANCE (FWA)
The difference in draught when the vessel moves from salt water to fresh water. The amount one may submerse the appropriate saltwater mark when in fresh water.
FREEBOARD DECK
The upper most continuous watertight deck having permanent means for closing all openings to maintain water integrity. below which all openings in the vessels side have a permanent means for water tight closure.
WATER TIGHT
a structure is watertight when water cannot pass through it in either direction.
WEATHER TIGHT
in any sea conditions water will not penetrate the ship.
SUPER STRUCTURE
The parts of the ship other than the mast and rigging, built above its hull and main deck
SUPER STRUCTURE DECK
a deck forming the upper boundary of a superstructure.
