Ship Construction Flashcards
Define: freeboard deck
The upper most continuous deck that can be closed weathertight.
Assigned freeboard
The distance measured vertically downwards at amidships from the upper edge of the freeboard deck to the upper edge of the summer load line
Weathertight
In any sea condition water will not penetrate the ship
Define Panting
Panting is the in and out movement of the shell material due varying pressure changes
Briefly explain how the locality is stiffened to resist this stress (Panting)
Reduce the unsupported opener area by close frame spacing and/or additional stiffening members (eg panting beams) and/or increase shell thickness
Wood - advantages
Floats, strength, appearance, easy to work with
Wood - disadvantages
Rots,
expensive
poor radar reflector
Steel - advantages
Relatively strong, widely available easy to work with cheap good radar reflector.
Steel - disadvantages
Corrosion,
relatively heavy
conducts heat
needs regular maintenance
Aluminum- advantages
High strength to weight ratio, doesn’t corrode as easy as steel, good radar reflector
GRP/FRP - advantages
High strength to weight ratio,
non corrosive
low cost if moulds are used
Readily available
GRP - disadvantages
Blistering and delamination,
once of fire - burns intensely giving off toxic gas,
poor radar reflector
Specialist Labour
Explain How chemical corrosion in steel occurs
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
Discuss the factors and conditions that would cause chemical corrosion to be accelerated and how good ship design could reduce this
Accelerated by heat and moisture
Prevention : Good ventilation Reduce heat Avoid water traps Accessibility for preservation Regular inspection and maintenance
Center grider - importance/function
Furthest from the neutral axis
Contributes substantially to the Longitudinal strength to resist sagging and hogging
Receives load when in dry dock
Plate floor - importance/function
Vertical plates running transversely across the bottom to stiffen the bottom
Transfer loads from the tank top and gives support to the side and center griders
Shell material - importance/function
Watertight skin of the ship. Major part of the ships strength.
Efficiently unites the supporting longitudinal and transverse members the make up the framing system.
Upper deck -
importance/function
Furthest from neutral axis;
Top flange of the grider
Strength deck
Deck beam - importance/function
Part of deck framework (with griders)
Supports deck plating
Transfer loading to frames bulkheads and pillars
Beam knee - importance/function
Unites the beam and frame enabling stresses to be transferred from one to the other
They offer some resistance to racking
Transverse frame - importance/function
Part of the framing system
Receives the deck loading via the beams and transfer the load to the bottom structure
Transverse bulkhead - importance/function
Subdivides the yacht into separate compartments
Contain flooding and fire
They contribute greatly to the structural integrity of the ship by providing the primary resistance to transverse deformation and so resist racking
They also are efficient load bearers and effectively distribute loads to the adjacent structure
Pillar - importance/function
Supports deck and transfers loading downwards, the unsupported span of the beam is reduced and hence beam sections can be reduced in depth so the clear space
Where extra deck loading is need ie: helicopter
Give four items of information to be found on a general arrangement drawing
plan, profile and section views
Division into compartments (tanks, engine room, holds)
Location of bulkheads
Location and arrangement of superstructure
Parts of the equipment (winches, loading gear, bow thruster, life boats) Dimensions (Length, Breadth, Draft) Volumes of the holds (Cargo Capacity Grain & Bale) Tonnage Deadweight Engine power Speed (Service Speed) Class
Sketch and explain the term “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
Explain how the locality is stiffened to resist this stress (pounding)
Frame spacing reduced
Additional stiffeners introduced
Shell plating thickness increased
State two reasons/functions for fitting each of the following :
Deck beams
Supports deck plating
Transfers loads to frames
Transfers loads to bulkheads
Transfers load to pillars
Describe the routine maintenance necessary to ensure that a weather-tight door prevents ingress of water
Ensure rubber seals intact, paint free
Ensure securing arrangement fully functional and greased
No obstructions to door closure
Door fits frame, seals.
Sketch aluminum and steel immersed in slat water and connected electrically,
Explain how a current is caused to flow from one material to the other and how this gives rise to ‘galvanic corrosion’
The galvanic action is a form of electrolysis whereby different metals will react with one another to form an electric cell when they are placed in suitable medium (an electrolyte)
In this case the less noble metal is the aluminum which will give up its ions and 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
Describe a method of cathodic protection
Sacrificial -
That galvanic action is an electro-chemical form of corrosion where one fo two dissimilar metals are eaten away. The metal that is eaten away is the one higher in the galvanic series ( ie the ignoble or anodic end) to counteract this in respect to mild steel, a metal more ignoble/anodic eg zinc or magnesium may be used and these are termed sacrificial anodes which will waste in presence to the steel
Describe another method of cathodic protection
Impressed current
That galvanic action is a flow of electrical particles (iones) through an electrolyte (SW) from the anodic metal to the cathodic metal - i.e an eclectic current. 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 controller rectifier and anodes
Sketch a ship being made to hog in a seaway
Explain why the upper deck will be subjected to high stress
As neutral axis is below half depth of vessel, tensile stress will be high
State four tasks provided by a classification society
Construction rules Statutory authority Material spec Insurance premium Resale value Surveyors available
Explain the term ‘fresh water allowance’
Amount by which the summer mark can be immersed when in FW due to less dense FW allowing floating at correct marks when emerging into higher density SW
Advantages and disadvantages of -
Aluminium alloy
Advantages -
Easy to work with
Less maintenance
Light
Disadvantages-
Melts at lower temp than steel
bi-metallic corrosion
Distortion with welding
Sketch a pumping system that could be fitted to a yacht
Identify all the associated valves and fittings
Needs to have- Mud box Strum Vale’s Fwd-middle-laz sections Holding tank Pump/s Disch-ashore facility O/b discharge Others
Sketch -
Sagging
Compressive stress in deck
Tensile stress in keel
Sketch -
Racking
Swell/waves on the beam of the vessel
Sketch -
Panting
+ & -
Panting is an in-and-out movement of the shell plating resulting from the variations of water pressureas waves pass along the hull and when the vessel pitches.
Sketch -
Pounding
Bow lifting at the crest of a wave and slamming/pounding in the trough of the next
Explain-
Reserve buoyancy
Intact volume between waterline and freeboard deck
Explain-
Gross tonnage
Internal volume of ship
Explain-
Net tonnage
Gross tonnage less deductions
A yacht is to undergo an annual survey.
State four items that would be inspected
Any examples of weather tight openings (doors, hatches, vent openings, side scuttles). Stability data, general structural condition
Explain -
Camber
Is the transverse curvature of the deck
Explain-
Flare
Is the outward curvature of the bow
Explain why camber may be incorporated in a yachts design
To shed water from the deck. Provides additional longitudinal strength
Explain why flare would be incorporated into a yachts design
Increases buoyancy of the bow - helps head up. Reduces breaking water on deck
A motor yacht with a steel hull is to have a 300mm hole cut in the bottom plating amidships in order to install an underwater fitting
i)Explain how stresses would arise in this vicinity
High stress area already due to being amidships (tensile/compressive) and farthest from neutral axis
Change of section due cutting of hole will cause stress lines to be concentrated
A motor yacht with a steel hull is to have a 300mm hole cut in the bottom plating amidships in order to install an underwater fitting
ii)describe the structural compensation that should be fitted in way of opening
By use of an insert plate of increased scantling with chamfered thickness reduction
Give four examples of information to be found on a general arrangement drawing
Side elevation/profile and plan of decks showing: accommodation; storerooms
Tanks bridge layout
Principle dimensions: LOA, LBP; opening/doors/windows/ports/scuttles/alleyways/ladders/companionways
Explain reserve buoyancy
Intact volume between waterline and freeboard deck
Explain the reason for fitting sacrificial anodes to a steel hull in the vicinity of a propeller made of non-ferrous material
The galvanic action (electro chemical process)-
Is a form of electrolysis whereby different metals will react with one another to form an electric cell when they are placed in a suitable medium (an ELECTROLYTE)
In this case the less noble metal is the zinc which will give up its IONS and become eaten away (it corrodes)
The zinc is known as the ANODE
Whilst the prop non ferrous metal becomes the a CATHODE.
The process is speed up due to the efficient salt water electrolyte
Explain the term sheer?
Give two reasons why the upper deck of a yacht might be given sheer?
Rise of the deck above the horizontal.
Added buoyancy forward, keeps head dry, aids drainage
Explain, with reference to galvanic corrosion, why the means of joining aluminum superstructure to a steel upper deck needs to be carefully made?
Galvanic corrosion is an electrochemical process whereby one metal corrodes in preference to another metal the it is in contact with through an electrolyte.
In this case aluminum is anodic to steel and needs to be insulated
(Example of an insulated product is ‘triclad’)
Give any explain of ‘discontinuity of strength’ in a yacht’s construction and explain how stress concentration will arise in the vicinity?
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. After a long period this will cause the structure to fail by cracking. This can cause corrosion in steel, and weld fractures particularly in aluminum
Summarize the Lloyds notation below
X100A1
LMC
UMS
100 - considered sutiable for seagoing service
A - built in ACCORDANCE with lloyds class rules
1 - anchor and mooring equipment comply with lloyd’s class rules.
X(Maltese Cross) New ship built under supervision of a society surveyor
LMC Lloyds Machinery Certificate
UMS unmanned machinery spaces
What is assessed/checked during an annual survey
General condition of the vessel,machinery and equipment
Other items include:
Closing appliances such as, hatches, ventilators and air pipes
Water tight doors and bulkheads
Steering arrangements
The provision of structural fire protection is verified
Anchors and cables
Disadvantages of aluminum?
Weaker than steal (half strength) More expensive Special technique to weld Not fireproof Not ecologically friendly.
Illustrate how dissimilar metals should be fitted
Can’t be touching
Washes rubber plastic
