Ship Technology Flashcards
What are docking strains?
Temporary static forces imposed on the ships structure during docking periods
Ships hull is no longer supported by the water, the ships hull tends to settle in a state of hog on the docking blocks
Draw docking strains/ aft cut up shores
Docket
Draw and describe hogging
Docket
Ship is supported midships by the wave crest while the ends are unsupported
Draw and describe sagging
Docket
Hull is supported at each end by the crests of adjacent waves while midships is unsupported
Draw and describe racking
Docket
External force (wind or wave) on one side of the vessel will tend to change the section so that the sides are no longer perpendicular to the ships bottom
What is B quality steel used for
Highly stressed areas of the ships structure where crack arresting properties are required
What is BX steel
Improved quality of B quality over 18mm thick
When is grade D steel used
Main ships structure except in highly stressed areas and where crack arresting properties are required
What are the advantages and disadvantages of aluminium
Adv
Density is 1/3 of that of steel and strength 1/2 of steel
Disadv
Aluminium looses strength at 250°C and melts at 650°C
Structural uses are severely limited and not used for primary structures, ladders or deck plates
When is aluminium used
Where weight is an important consideration and for minor bulkheads
Advantages of steel
Weldable
Strong
Relatively cheap
Available
Ductile
Disadvantages of steel
Corrodes
Heavy
Magnetic
Subject to failure
What is the definition of ductile
Ability to define before failure
What is the definition of toughness
Ability to absorb energy
What is the definition of strength
Ability to resist deformation and retain its shape
Describe the 3 categories of structure
Primary, contributes to main structural strength and maintains water tight integrity
Secondary, doesn’t contribute to structural strength but does contribute to water tight integrity and supports local loads
Minor, doesn’t contribute to structural strength or watertight integrity
Describe the keel
Flat and vertical keels run fwd to aft
Maximum strengths is at midships to resist against hogging and sagging
Vertical keel is designed maximum strength to resist forces encountered when docking
Where access holes are cut in vertical keel a rider plate must be fitted for the loss of strength
Label the strength members of structure
Docket
What is the purpose of the water tight subdivision
Divide the buoyant volume of the shop into smaller compartments and preserve the largest amount of buoyancy in the event of the hull being damaged
The underwater volume and a large amount above must be made watertight
The closer the subdivision the more unsinkable a ship becomes
What parts of the ship contribute to water tight integrity?
Decks
Bulkheads
Double bottoms
Collision zone
Describe the function of main transverse bulkheads
Effectively divide the hull of the ship into separate sections
Overall stiffening of the ships structure
Reduce effects of damage to the ship
Withstand pressures associated with flooded compartments
Valves fitted when ships systems pass through main transverse bulkheads
What is the function of a collision bulkhead
Provide watertight barrier from 1 deck to the keel in event of damage to the bow section
Resists hydrodynamic pressure upto cruising speed
What is the function of a deck?
Strength members acting horizontally to maintain the hull shape
Form water tight subdivision
Act as platforms and boundary’s of compartments and support equipment
Worked intercostally to the MTB (except strength deck)
What is the strength deck
Uppermost continuous deck from the neutral axis
Made of B quality steel
What is the superstructure
All structure above the strength deck
Offices, accommodation, workshops and hanger
Additional support for bridge funnel masts and weapon directors
Contributes little to structural strength
Supported by MTBs underneath
Local stiffening is provided for RAS/davits
Aluminium may be used where weight is a consideration
How are water tight hatches fitted
Extending the rider plate which prevents water from spilling into the compartment below
What are the two groups of hatches and how are they secured
Normally closed at sea- tumbler bolts
Access to compartments normally manned or frequently visited - clips
What is fitted when a hatch is cut into to the deck
Carlings and half beams to compensate for the loss in strength
Describe shaft brackets
Supports the weight of the shaft
Strong enough to support the loss of a propeller blade
What does each shaft bracket consist of
Barrel
Arms
Palms
What bearing is used in the barrel
NF21 or Orkot
Describe the palms
Welded to longitudinale or vertical floors in the ships structure
Fitted parallel to she ships structure
Shell of B quality steel is welded to the palm and ships shell where it passes through the hull
What are the 4 types of corrosion
Oxidation
Electrolytic
Bacterial
Chemical
What 2 organisations assist with surveys?
Lloyds register
MCTA Hull survey team
When are the NSSC conducted?
Initial survey
Renewal survey
Periodic survey
What is the periodicity of the NSSC?
Survey on an annual basis may be required for certain ships that are known to have particular deficiencies
All surveys should take place within plus or minus 3 months
Why are surveys undertaken?
Ensure hull, upper deck, structure, compartments fixtures and and fittings are kept to a high standard
Ensure water and gas tight integrity of the ship
How is corrosion recorded?
Depth and area of corrosion
Light surface, less than 1mm
Medium surface more than 1mm but less than 70% of plate thickness
Heavy more than 70% of plate thickness
How can the area of corrosion be described?
Localised
Scattered
Extensive
When is compartments air testing carried out?
Every 6 years
If work carried out on compartment boundaries
If in doubt of water tight/ gas tight integrity
What compartments is air testing carried out in?
Red risk zone
Flammable gases or ammunition
Boundaries of compartments with halon or carbon dioxide drench systems
Safety precautions to be observed when air testing?
Don’t station a person in compartment where only 1 entry/ exit point
Don’t leave person in too long when carrying out vacuum test
Maintain positive communication with the person
All pressure is released from compartment prior to releasing the door
What is the gutter strake?
Middle line of inner bottom plating forming the rider to the vertical keel
Why are anchors and cables surveyed?
Ensure it is fit for purpose and not unduly worn
Who carries out the survey for cables and anchors?
A surveyor from an approved classification society
Or
An authorised navel base personnel
What qualifications are required to carry out survey on anchors and cables
Appropriate training
Accredited qualifications
Hold responsible officer status.
What is the procedure for surveying ladders?
Check security of fastenings on all treads
Check handles for distortion and security
Check stringers for distortion and corrosion
Check backplate for security and noise
Check hinge positions for security and distortion
Checked in accordance with maintenance schedule
What 4 strength members prevent hogging and sagging?
Decks
Longitudinals
Keel
Double bottom
