7.(a) Describe what is meant by Continuous Class Machinery Surveys.
(4)
(b) State FOUR reasons why the fuel efficiency of a vessel maybe less than the build sea trials data.(4)
(c) List FOUR typical defects which may reduce the output of a centrifugal pump.(2)
7.(a) Continuous Class Machinery Surveys (4 marks)
- A system of machinery survey where, instead of all machinery being inspected at fixed survey intervals (e.g. every 5 years), the inspection is spread continuously over the vessel’s normal service period.
- Machinery items (main engine, auxiliaries, boilers, pumps, steering gear, etc.) are examined by the Classification Society surveyor in rotation at agreed intervals.
- Each item is surveyed during normal maintenance or overhauls, so the ship does not need to undergo prolonged lay-up solely for survey purposes.
- When all items in the schedule have been completed, it is equivalent to a full Special Survey, thereby maintaining the vessel “in class.”
7.(b) Reasons why fuel efficiency may be less than build sea trial data (4 marks)
- Hull fouling – accumulation of marine growth and slime increases resistance.
- Propeller surface roughness or damage – reduces propulsive efficiency.
- Machinery wear and reduced efficiency – e.g. turbocharger fouling, worn injectors, reduced compression.
- Operating conditions differ from sea trials – e.g. heavier loading, different draught/trim, adverse weather or sea state.
7.(c) Typical defects reducing output of a centrifugal pump (2 marks)
- Impeller wear, erosion, or corrosion.
- Blocked or clogged suction strainer.
- Air leakage into suction line (loss of prime).
- Worn bearings or gland/shaft seal causing loss of efficiency.