Ship Construction/Electrical Flashcards
With reference to transferring large quantities of fuel from low tanks, such as double bottom storage tanks, to higher wing bunker tanks:
(a) Explain the possible effects on the stability of the vessel; (8)
(b) State the important checks to be made before and during the fuel transfer operation. (8)
a) This could have a significant effect on the stability because by doing this you are raising the center of gravity to the whole vessel and reducing the GM. Depending on the initial GM and the amount of oil being transferred you could give the vessel a negative GM and cause it to capsize. The chief officer should always be consulted before any such movements.
The vessel will become less stable as the distance of GM decreases as the center of gravity of the ship rises. If the fuel is moved from central double-bottom tanks to wing tanks, it will effectively give the fuel a greater moment which could amplify roll in rough weather.
(b) State the important checks to be made before and during the fuel transfer operation. (8)
(b) Important checks to be made before and during the fuel transfer operation
Check with the chief officer.
Ensure there is adequate room in the destination tank.
Ensure that the fuels can be stored together if they were bunkered at different places.
Sound the tanks before and after and ensure all fuel that has moved can be accounted for.
Ensure the overflow tank is empty,
Where possible the transfer should be mirrored on both sides of the vessel.
When all the above are satisfied, proceed as follows
Open the correct valves.
Start the pump and check the suction and discharge pressure.
Check the running amps of the pump.
Check fuel tank temperature.
Frequent sounding of tanks to be taken.
With reference to transferring large quantities of fuel from low tanks, such as double bottom storage tanks, to higher wing bunker tanks:
(a) Explain the possible effects on the stability of the vessel; (8)
(b) State the important checks to be made before and during the fuel transfer operation. (8)
- With reference to transferring large quantities of fuel from double bottom storage tanks to wing bunker tanks
a. Explain the possible effects on the stability of the vessel (8)
• The deck department should be informed in order to ballast the vessel correctly to compensate for list, trim and draught
• The centre of gravity will be altered due to the weight change of both the double bottom tank and the wing tank
• The free-surface effect is increased on tanks that are not full
• As the fuel is consumed the vessel becomes light, reducing the draught making it more susceptible to sharp rolling
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b. State important checks to be made before and during the fuel transfer operation (8)
• No ballast operations are in progress that may be detrimentally effected due to further changes in position of mass
• There is sufficient volume remaining within the receiving tank
• Fuel should be taken from double bottom tanks evenly to reduce the stress subject to the ship’s hull
• The correct fuels are being transferred, of similar densities and sulphur contents
Q9
Explain the meaning and purpose of EACH of the following ship terms:
(a) Transverse watertight bulkhead (4)
(b) Bilge keel (4)
(c) Shear strake (4)
(d) Cofferdam (4)
- Explain the meaning and the purpose of:
a. Transverse watertight bulkhead (4)
A watertight bulkhead is used to divide a ship into a number of water tight compartments; this would decrease the
spread of fire and water if the shell plate was damaged. The watertight bulkhead also adds to the transverse strength of
the ship
b. Bilge keel (4)
Bilge keel is a long fin like bit of metal welded along the length of the ship externally on the bilge radius, employed in
pairs, 2 each side, designed to restrict the amount of roll a vessel suffers this enhancing the stability of the ship.
c. Shear strake (4)
Attaches the side shell to the upper deck or weather deck, giving strength to the upper deck and maintain the shape of
the side plating and also protecting the ship from water entering.
d. Cofferdam (4)
An empty void like space/compartment situated between two tanks or watertight bulkheads. This can be used to check
for any leakages in either one of the tanks, or if there is a leakage it will prevent contamination between the two tanks.
Q9
Explain the meaning and purpose of EACH of the following ship terms:
(a) Transverse watertight bulkhead (4)
(b) Bilge keel (4)
(c) Shear strake (4)
(d) Cofferdam (4)
(a) transverse water tight bulkhead - It is a bulkhead that stretches the full breadth and from bottom plates to the main upper deck. It prevents the spread of water and fire whilst also providing strength to the vessel which stops racking.
(b)Bilge keel- A stiffened plate that is welded to the outside hull plating. Acts as a passive stabilizing device which reduces the severity of ships rolling.
(c)Shear strake- The top line of ship’s side plating running adjacent to the weather deck. The plate is required to be of higher strength, either thicker plate or higher tensile material.
(d)Cofferdam - A tank used to segregate and resist cross-contamination of different liquids, or the engine room. A cofferdam would be found between a fuel storage tank and a ballast water tank, if the fuel tank were to form a crack internally, it would leak into the cofferdam instead of contaminating the ballast water.
Q6
With reference to main distribution systems fitted with preference trips:
(a) State why the preference trip is fitted. (2)
(b) Explain the operation of a THREE stage trip. (8)
(c) State THREE circuits that can not be connected to the preference trip giving a reason for EACH (6)
a) Preferential trips is a technique to avoid overloading. Non-essential services will be tripped to reduce the load on the generator.
(b) 3 stages of preferential trip are:
1st stage: tripping will occur if the generator runs at 110% of its rated load.1ststage is activated after 5 seconds of time delay. For example: GALLEY SWBD.
2nd stage: the tripping will occur after 10 sec if the load is not normalised by the 1st stage. For example: AC and ventilation.
3rd stage: the tripping will take place after a 15-second time delay if the load is notnormalised by the 2nd stage. For example: the refrigeration plant.
(c) 3 essential equipment that cannot be connected to preferential tripping are:
Fire fighting
Steering and propulsion.
Bilge and ballast system
What is a preferential trip?
iv) Preferential trips: A preferential trip is an electrical arrangement which is designed to disconnect
the non-essential circuits (non-essential load) from the main busbars in case of partial failure or overload of the main supply. If a generator overload occurs, the preferential trip relay will set an
alarm and acts to trip selected non-essential loads. This tripping of non-essential loads helps to
reduce the generator load, allowing it to continue to supply essential loads and maintain its normal load. The non-essential loads will be services such as air conditioning, ventilation, galley, and laundry
services etc.
Q7
With reference to electrical motors:
(a) State the routine maintenance that is necessary (8)
(b) Describe the tests carried out to prove good electrical condition. (8)
With reference to electrical motors:
(a) State the routine maintenance that is necessary (8)
(b) Describe the tests carried out to prove good electrical condition. (8)
(a) Regular maintenance that is necessary for good electric motor operation
Make sure the motor is tightly secured and free from vibration.
Ensure regular insulation resistance readings are taken and values obtained are recorded.
Make sure that the motor shaft is turning freely.
Lubricate the bearings only when scheduled or if they are noisy or running hot. Do NOT over-lubricate.
Wipe, brush, vacuum or blow accumulated dirt from the frame and air passages of the motor.
Make sure the motor is dissipating heat correctly and it is well-ventilated.
Check if the motor’s electrical connections are tightly secured and the correct labels are secured.
Regularly check the state of motor windings for integrity.
Do not allow fins to become overpainted
(b) Insulation Resistance Test: This test is carried out with the aid of an appropriately rated IR Tester (Megger). Before applying any electrical test, appropriate safety paperwork such as Risk Assessment and Permit to Work is completed; this will ensure that the motor is isolated and it is safe for the test to be carried out. To prove the basic operation of the tester, short the two probes together and press the ‘test’ button. The display should read 0Ω. For an IR test on a three-phase machine, measure and log the phase-to-phase insulation resistance values. Three readings should be measured as U-V, V-W, and W-U. Measure and log the phase-to-earth insulation resistance values. Three readings should be measured as U-E, V-E and W-E.
Continuity Test: Appropriately rated multimeter is set to ‘continuity’ and interconnections of motor terminal connections are removed so we have both ends of each winding. Test probes are applied, in turn, to each end such as U1 and U2 and checking the multimeter to give continuity indication.
Balance Test: This test is carried out with the aid of an appropriately rated multimeter. Resistance readings for each winding are obtained. A good motor will show that each winding resistance is similar to other windings.
Q7
With reference to electrical motors:
(a) State the routine maintenance that is necessary (8)
(b) Describe the tests carried out to prove good electrical condition. (8)
- With reference to electrical motors
a. List four maintenance criteria that is necessary for good operation (8)
• Motor cooling fins and fan housing free from dust or debris
• Electrical insulation in good condition
• Bearings are in good condition and well lubricated
• Shaft is well aligned
• Make sure its secured
c. Define the regular maintenance that is necessary for good electric motor operation (10)
• The testing of insulation resistance of field windings to ensure they are sound
• Regular lubrication of shaft bearings with high quality lubricant
• Routine cleaning of fan cages, fan blades and casing fins
• Routine balancing of rotor shafts
• Routine checks of shaft alignment, observe vibration during running potential worn bearings
b. Describe how to test for electrical faults within an electrical motor (8)
• Risk assessment carried out
• Isolate the motor mechanically and electrically, tag and lock all areas of electrical supply
• Remove the electrical cover and test that there is no electrical supply (prove dead)
• Using an approved insulation resistance tester measure between all phases and the casings, also between all phases
• Measure the resistance of the windings and log results
• Balance test to make sure windings are balanced
