Ship Construction / Electrical Flashcards
Q6
With reference to marine electrical distribution systems:
(a) State the meaning of the term insulated neutral. (8)
(b) Briefly describe how the location of an earth fault can be found. (4)
(c) State the safety precautions to be taken before investigating faulty electrical machinery. (4)
(a) Insulated Neutral:
An insulated neutral distribution system is one in which the main generator’s neutral point is kept away from the ship’s hull.
Insulated neutral systems are preferred on low-voltage ships operating at 440V AC.
(b) Earth faults can be located by the process of elimination.
Power is switched off to a certain area in a pre-determined order. Personnel in the area must be alerted before doing so, and someone must keep an eye on the fault monitor until it clears.
Once the general location has been found, go there and conduct an insulated resistance test to locate the exact location
(c) Safety precautions to be taken before investigating faulty electrical machinery
A competent person must conduct a risk assessment to implement control measures.
The electrical circuits to be investigated will be safely isolated.
Safe isolation means switching off the power, locking it in place with a safety lock and posting appropriate notices: caution if the circuit is dead and danger if working on the live circuit
Q6
With reference to marine electrical distribution systems:
(a) State the meaning of the term insulated neutral. (8)
(b) Briefly describe how the location of an earth fault can be found. (4)
(c) State the safety precautions to be taken before investigating faulty electrical machinery. (4)
- With reference to marine electrical distribution systems:
a) State the meaning of the term insulated neutral (16)
In a neutral insulated system, a single earth fault occurring in the system would not cause any earth current to flow in
the ship’s hull. This is because a single earth fault current does not provide a complete circuit for earth current to flow.
So no protective trip will operate and system will continue to function normally
b) Briefly describe how the location of an earth fault can be found (8)
Earth fault location is traced by process of elimination. Before the process is applied personnel whose space may be
affected must be informed. Power is then switched off in a pre-determined order while keeping an eye on the earth
fault monitor to see if switch off the power has cleared the fault. Once the general location of the fault has been
located, insulated resistance test is carried out to locate exact location of the faulty circuit.
c) State the safety precautions to be taken before investigating faulty electrical equipment (8)
Correct risk assessments are to be carried out by the competent person to put in place the control measures. After this,
electrical circuits are to be investigated and made sure safely isolated. Safe isolation will mean switching off the power,
securing the power switch, posting appropriate notices to be displayed to let other engineers know of the work, and
finally the circuit is proved dead
Q7
With reference to a small 3 phase electrical motor driving a transfer pump that is not used on a regular basis failing to rotate when the start button is pressed:
(a) Outline the procedure to determine the possible cause. (8)
(b) Explain the procedure to remove the motor should it be faulty and require changing. (8)
(a) When the motor fails to rotate on pressing the start button, then there may be two general reasons for the motor failing to start: Mechanical and Electrical.
Mechanically, bearings may have become seized, or the gears may have been seized. In both cases, the motor will overheat rapidly, producing unusual noise as it tries to rotate the pump.
Ensure that the power supply is switched on and also is available at the motor terminals. This can be tested with the aid of a multimeter.
If the power supply is proved to be available at the terminal block, this indicates that the fault is inside the motor.
A continuity test is carried out to determine whether the phase windings are continuous (electrically) and not damaged.
Once the continuity of the windings has been proved, other tests, such as megger, should be carried out.
(b) Procedure to remove the motor for replacement:
Before work is carried out, the motor and its attached pump are safely isolated both mechanically and electrically as per the ship’s SMS requirements.
Electrical isolation will involve switching off the power securing switch off so that it cannot re-energise even accidentally.
Posting notices to let other engineers know of the work being carried out.
Ensure correct PPE, tools, sufficient lighting, and appropriate and certified lifting equipment are available.
The motor is then uncoupled from the pump and safely stowed in a designated storage space.
The work area itself was secured until the fitting of the new motor to protect the pump.
Q7
With reference to a small 3 phase electrical motor driving a transfer pump that is not used on a regular basis failing to rotate when the start button is pressed:
(a) Outline the procedure to determine the possible cause. (8)
(b) Explain the procedure to remove the motor should it be faulty and require changing. (8)
- With reference to small 3 phase electrical motor, driving a transfer pump that is not used on a regular basis, failing
to rotate when the start button is pressed:
a. Outline the procedure to determine the possible cause (8)
• There may be two reasons for non-starting of the motor; mechanical and electrical. Mechanically, bearings may
have become seized, or the gears may have been seized, in both cases motor will overheat rapidly producing
unusual noise as it is trying to rotate the pump
• Ensure that the power supply is switched on and available at the motor terminals. This can be tested with the
aid of an appropriately rated potential indicator.
• If the power supply is proved to be available at the terminal block then this is indicating the fault is inside the
motor
• Inside the motor, few electrical tests are carried out such as continuity test to see if the phase windings and
continuous and are not damaged
• Once continuity of the windings has been proved, then other tests such as megger should be carried out.
b. Explain the procedure to remove the motor should it be faulty and require changing (8)
• Correct risk assessment carried out
• Prior to work being carried, motor and its attached pump is safely isolated both mechanically and electrically
• Electrical isolation will involve switching off the power, securing switch off so that it cannot be turned on by
accident, posting notices to let other engineers know of work being carried out, prove dead also
• Ensure correct PPE, tools, sufficient lighting, appropriate and certified lifting equipment are available
• Motor is then uncoupled from the pump, safely stowed to a designated storage space
• Work area itself secured until the fitting of new motor to protect the pump
Q8
(a) State the measurement that gives an indication of a ship’s stability. (2)
(b) Explain the meaning of the measurement stated in (a). (2)
(c) Explain how the measurement given in (a) indicates EACH of the following:
(i) Stable stability. (4)
(ii) Unstable stability. (4)
(iii) Neutral stability. (4)
ago
(a) GM is the measurement that indicates a ship’s stability
(b) It is the distance between the ship’s centre of gravity and metacentre.
(c) (i) Stable Stability:
If the metacentre point is above that of the centre of gravity the GM is positive and the ship is stable
(ii) Unstable stability:
If the metacentre is below the centre of gravity, then GM is negative and the ship is unstable and could capsize.
(iii) Neutral stability:
This condition is where the GM is zero i.e. the metacentre and the centre of gravity are at the same point.
Q8
(a) State the measurement that gives an indication of a ship’s stability. (2)
(b) Explain the meaning of the measurement stated in (a). (2)
(c) Explain how the measurement given in (a) indicates EACH of the following:
(i) Stable stability. (4)
(ii) Unstable stability. (4)
(iii) Neutral stability. (4)
- a) State the measurement that gives an indication of a ships stability
GMT measurement, the distance between the transverse metacentre and the vertical centre of gravity (GM)
b) Explain the meaning of the measurement stated in Qa)
This distance determines how stable a ship is, if the distance is small the ship is less stable than if the distance is larger.
c) Explain how the measurement given in Qa) indicates each of the following
(i) Stable stability
This is when the M value is higher than the G Value
(ii) Unstable stability
This is when the G value is higher than the M value
(iii) Neutral stability
This is when the G value and M value are at exact same point
Q9
Explain the meaning and purpose of EACH of the following ship terms:
(a) Hawse pipe. (4)
(b) Chain Stopper. (4)
(c) Fairlead. (4)
(d) Bollard. (4)
(a) Hawse pipe:
The usual position for the stowage of the ship‘s anchors. The hawse pipes facilitate the run of chain cable when letting go the anchor.
(b) Cable stopper:
A fitting used to secure the anchor chain when riding at anchor, thereby relieving the strain on the windlass, and also for securing the anchor in the housed position in thehawsepipe. Chain stopper usually consists of two parallel vertical plates mounted on a base with a pivoting bar or pawl which drops down to bear on a chain link.
(c) Fairlead:
A Fairlead is a device used to guide a line or rope in a specific direction. Its purpose is to prevent the line from chafing against the ship’s structure and to ensure that it is properly aligned with the winch or other device that is handling it.
(d) Bollard:
A Bollard is a sturdy, short, vertical post. Its purpose is to secure a ship’s mooring lines and to prevent the ship from moving. It is often used in pairs, with one on each side of the ship.
Q9
Explain the meaning and purpose of EACH of the following ship terms:
(a) Hawse pipe. (4)
(b) Chain Stopper. (4)
(c) Fairlead. (4)
(d) Bollard. (4)
- Explain the meaning and purpose of EACH of the following ship terms:
a) Hawse pipe: Tubes that lead from the shell plating to the forecastle deck, providing a channel for
the chain to run and be cleaned as water spray cleans the anchor chain during heaving. The pipe
absorbs 20% of the minimum breaking strain of the chain.
b) Chain stopper: Fitted in order to hold the anchor in place while the ship is underway. The chain
stopper guides the chain during anchoring manoeuvres and absorbs the pull of the chain by diverting
it to the hull.
c) Fairlead: Has a roller attached to it to guide mooring wires to winches for the correct lead, roller
fairleads can be vertical or horizontal.
d) Bollard: Are short vertical posts to secure the ships mooring lines, they withstand strong forces
often present during mooring.
Q9
Explain the meaning and purpose of EACH of the following ship terms:
(a) Hawse pipe. (4)
(b) Chain Stopper. (4)
(c) Fairlead. (4)
(d) Bollard. (4)
- Story Analogy: “The Chain’s Journey”
Imagine a giant anchor chain on a ship — this is its path:
1. Hawse Pipe:
Where the anchor chain first exits the ship’s hull at the bow.
• Looks like: a sloped pipe through the ship’s bow.
• Function: guides anchor chain from chain locker to sea.
• Location: forward, under the forecastle deck.
2. Chain Stopper: The “brake” for the anchor chain. • Function: holds the chain and takes the load off the windlass once anchored. • Location: Between windlass and hawse pipe. • Think of it as a clamp or lock that grabs the chain. 3. Fairlead: A guide for mooring ropes or chains to avoid friction/damage. • Looks like: rollers or eyelets. • Function: guides ropes/chains in the correct direction. • Location: Near deck edges, often at chocks or near bulwarks. 4. Bollard: What you tie the ship’s ropes to onshore or on deck. • Function: securing mooring ropes. • Looks like: a twin post or strong pillar. • Location: On deck or quayside
What does a hawse pipe look like and chain-stopper on board?
What does a fairlead look like on board a ship?
