Ships technology Flashcards
draw docking strains
see drawing
describe docking strains
- temporary static forces can be imposed in the ships structure during a docking period, now as ‘docking strains’
- being no longer supported by the water, the ships hull will settle in a state of ‘hog; when on the docking block
draw the two conditions of stress
see hogging and sagging drawings
describe hogging
in this condition the ship is supported mid ships by thr wave crest whilst the ends are unsupported
describe sagging
in this condition the hull is being supported at each end by the crest of adjacent waves whilst the mid ships section is unsupported
describe racking
external forces on one side of the vessel will tend to change the section so that the sides are no longer perpendicular to the ships bottom
draw racking
see racking drawing
list the commercial grades of steel there’s uses, and a description of them
- B quality steel, used in more highly stressed areas of the ships structure or where crack areasting properties are required
- BX grade, is an improved form of B quality but over 18 mm thick. Used in keels on large warships and rudder bridge assemblies
- D grade, Mild steel with guaranteed toughness, ships structure but not highly stress areas or where crack arresting properties are requires
what are the advantages and disadvantages of steel ?
Advantages
- weldable
- strong
- relatively cheap
- available
- ductile
Disadvantages
- corrodes
- heavy
- magnetic
- subject to failure
what is the use of aluminium on ship?
- used where weight is an important consideration
- ## minor bulkheads
what are the advantage as and disadvantages of Aluminium?
Advantages
- density is 1/3 of steel, strength 1/2 of steel
- non- magnetic
disadvantages
- looses strenght at 250 degrees
- melts at 650 degrees
- high maintenance
what are the three categories of ships structure give a description and example of each?
Primary, which contributes to the main structural strength of the vessel, hull plating, framing principal decks and main watertight bulkheads
secondary, which dose not primarily contribute to structural strength but does to the watertight integrity and supports local loads
Minor, structure that contributes to neither structural strength nor watertight integrity
what is the difference between an RN ship and a merchant ship?
- all superstructure blocks should be supported at each end by transverse bulkheads underneath
- the structure must be arrange so the discontinues of strength do not occur, stress concentrations and serious local strains may result
- each separate compartment on board contains equipment with special roles, this subdivision aids WT integrity and provides a margin of safety
- decks and bulkheads are fabricated from steel, they help support the local stress loading associated with masts, wepons
discribe the keel
- both the flat and vertical keels run continuously from fwd to aft and vary in scantling along their length
- the keels max strength is at midships to resit bending moments, from hogging and sagging
- the vertical keel has its deigned max strength in the way of the aft cut-up to resit forces from docking
- when access holes are cut in the vertical keel, a rider plate is always fitted to compensate lossed strength
discribe a double bottom
1 mark answer
double bottoms consist of two watertight bottoms with a void space between them
discribe double bottoms
lots of marks answer
Double bottoms consist of two watertight bottoms with a void space between them
They are strongly constructed and can withstand the upward pressure of the sea, in addition of the bending stresses
They provide a storage space for fuel oil, fresh water, and salt water ballasts
They can withstand considerable bottom damage caused by grounding or underwater blasts without flooding the ship provided the inner bottoms stays intact
what are the advantages of a double bottom
- provide additional protection
- contribute to longitudinal strength
- assist with watertight subdivision
- form tanks for the storage of liquids
- act as a second hull
available for counter flooding
Give a description of the inner bottom
the inner bottom is the watertight deck fitted on top of the plate longitudinal and transverse frames to form the double bottom
it helps maintain the WT integrity of the hull in the event of damage to the outer bottom and contributes to the longitudinal strength of the hull
give a description of a gutter strake
middle line of inner bottom plating forming the rider to the vertical keel
label the inner bottom plating
see image
what is the purpose of watertight subdivision
- to divide the buoyant volume of the ship into smaller compartments and preserve the largest amount of buoyancy in the event of the ships hull being pierced
- the preserve buoyancy the underwater volume and large amount above must be made into watertight boxes
- the closer the subdivision the more unsinkable a ship becomes
how is watertight subdivision achieved
- main transverse bulkheads
- main longitudinal bulkheads
- WT bulkheads, decks and flats
- double bottoms and tanks
what are main transverse bulkheads (MTBs)
-large bulkheads which effectively divide the hull of the ship into separated section
-the stiffen the ships structure
- reduces the effects of damage to the ship
-the positioning of these WT bulkheads allows the ship to fulfill the requirements for damaged stability, enabling them to withstand the pressures associated with flooded compartments
-watertight valves are fitted to allow necessary systems to pass through the MTBs
-
describe collision bulkheads
provides a watertight barrier from no.1 deck to the keel in the event of damage to the bow
resist hydrodynamic pressure up to crusing speed
describe decks
- horizontal strength members acting to maintain the hull shape
- in conjunction with bulkheads, they form wt sub-divisions
- act as platforms and boundaries of compartments
apart from the strength deck they are worked intercostally to the main transverse bulkheads
describe the strength deck
the uppermost continuous deck farthest from the neutral axis
what is the superstructure
- it contributes to little structural strength
- comprises all the structure above the strength deck
- it provides space for officers accom, workshops, hanger
- support for the bridge, funnel, masts and weapons directors
- to avoid stress all superstructure blocks should be supported at each end by transverse bulkheads underneath
- local stiffening is provided in way of davits, RAS point
- Aluminium may be used where top weight is consideration
draw a hatch
see drawing
what are the names of the surveying organisations?
LLoyds register
MCTA Hull survey team
what surveys are carried out in support of the NSSC
- Initial survey conducted before a ship is put in service
- a renewal servant at intervals not exceeding 5 years
- a periodic survey at intervals between the second and third anniversary date
- surveys may be required on an annual basis by Naval authority for certain ships that are known to have particular deficiencies
- surveys must take place within +or- 3 months of the anniversary
why do we survey
- they are undertaken of the ships hull, upper deck, structure, compartments, fixtures and fittings
- to make sure that they are kept in a high material standard
- to keep the ship the ship as near as possible to the same state as when first built
- to ensure gas tight and watertight integrity
what notes are take when doing surveys
- the state of coatings
- the degree of any corrosion
- the necessary remedial action determined
- when surveying confined spaces, notes should be taken by an assistant, who is also a safety number
what is the procedure once a ship is in dry dock?
- the outer hull is to be pressured washed to remove salt deposit that may accelerate corrosion
- it helps to reveal obvious areas that require immediate attention
-corrosion as the ships wind and water line is usually greater due to the amount of dissolved oxygen caused by the bow wave - particular atteion should also be paid to areas not fully painted.
- in the way of keel blocks, bottom, breast, bilge and cut up shores
- areas near the sonar
- areas near non-ferrous metals
- underside of keel near the afghan cut up
- shaft brackets rope guards and eddy plates
when and how are guard rails surveyed
- all guard rails are survey 6 monthly, comes up on UMMS
-before and after rigging - prior to docking down, the dockyard should survey them
the survey should take form of a routine examination of all stanchions, stays, wires, fittings and nets
what types of defects can be found on guard rails, when should they be rectified?
- distorted stanchions
- cracked welds
- missing parts
- defective fittings
- defects are to be rectified ASAP
- Distorted aluminium which can not be replaced may be straightened cold. Heat must not be used
what’s the procedure for surveying ladders?
whether internal or external, they are to be surveyed when it comes onto umms
- check security of fasting on treads
- check handrails for security and distortion
- check stringers for distortion and carrions, splitting on wooden ladders
- check backplate for security and noise
-check hinge positions foe security and distortion
what’s the procedure for carrying out cable surveys ?
- anchors, cables and associated equipment is subject to survey and test to ensure it is fit for purpose and not unduly worn
- the may only be carried out by a surveyor from an approved marine classification society or by authorised navel base personnel
- received the appropriate competency training
- have suitably accredited qualifications
- hold a responsible officer status certificate
what are the requirements for air testing an compartment
- to ensure watertight integrity
- every 6 years
- may be required is work has been carried out which could compromise the compartment
- not all compartments are required to be air tested, just those that are,
- in the red risk zone
- contains flammable gasses or ammunition
- forms boundaries for compartments able to CO2 drench
what are the safety requirements when air testing compartments
- maintain positive coms
- do not have people inside where the only access is a bolted manhole cover such as a tank
- do not leave a person in a compartment too long with out change in ventilation
- ensure all pressure had been discharge before open the last clip to the compartment
describe rudders
when a helm id applied, the side thrust on the rudder blade causes a large bending moment on the rudder stock
the lower bearing is subject to severe loading and therefore wear
on each occasion of routine docking, rudder clearances are measured to ensure maximum diametric wear is not exceed
what is the material a bearing off the shaft bracket is made of
NF21
ORKOT
why do we use shaft brackets and what do they consist of
- dynamic forces applied to the shaft by the prop would cripple the ship is there where not a constraint used
- this constraint must be string enough to support the shaft at its max perceived loading, which doe constructional purposes is assumed to be the loss of a prop blade
the major component of a shaft brackets are
- barrel
- arms
- palms
give a description of the palms and how it is fitted to the ship
the upper parts of the bracket arms formed into a palm plate which is welded to longitudinal or vertical floors
the longitudinal are strength and increased in depth to accommodate the palm plate
a shall insert or B grade steel is welded to the palm plate and the ships shell where is passes through the hull
plan plates are fitted parallel to the ships centre line
what are the main cause of corrosion ?
oxidation - the main form of corrosion or rusting
electrolytic action - caused by dissimilar metals
chemical action - acid attack in battery’s compartments
bacterial action - found in fuel tanks and bilges
how are corrosion and pitting defects typically described
depths and area
light surface corrison- less than 1 mm depth
medium - greater that 1 mm depth, wastage is less that 70% of plate thickness
heavy- wastage greater than 70% of plate thickness
the area is decried as,
- localised
- scattered
- extensive
