Lecture 1, 2 and 3

Question 1

What is the efficiency of a 2-stroke engine, including waste heat recovery (WHR)?

Answer 1

Efficiency of a 2-stroke engine is 49%. Waste heat recovery adds 5%, giving a combined efficiency of 54%.

Question 2

What are the waste heat recovery methods?

Answer 2

1. Exhaust gas turbocharger (300°C → 220°C): Converts energy for intake air compression.
2. Exhaust gas economiser: Produces steam for fuel heating.
3. Jacket cooling water: Generates freshwater using heat from engine cooling.

Question 3

What is a limitation of waste heat recovery?

Answer 3

Jacket water cooling temperature is restricted to 160 degrees Celsius to prevent falling below the dew point, as can cause condensation and corrosion.

Question 4

How is fuel prepared for a 2-stroke engine?
( In chronological order)

Answer 4

1. Bunker Tank: Stores fuel (~40°C).
2. Settling Tank: Heats to ~90°C; removes impurities.
3. Purifier: Removes water and solids via centrifugal force.
4. Service Tank: Heats fuel to 12-13 cst viscosity.
5. Filtration & Injection: Final heating (~125°C), filtration, and pressurized injection.

Question 5

How is air prepared for combustion in a 2-stroke engine?

Answer 5

1. Turbocharger compresses air to *3 bar and heats it (~165°C).
2. Air cooler reduces temperature to ~40°C, increasing density for efficient combustion.
3. About 8000 g of air is required to achieve a typical SFOC of 176 g/kWhr for a 2-stroke engine.
4. Cooler air increases air mass for effective combustion

Question 6

What three conditions must fuel meet before injection?

Answer 6

1. Correct viscosity (**12-13 cst).
2. High pressure for injection.
3. Free from contaminants through the process of fuel preparation from bunker tank, settling tank, purifier to service tank and through filters.

Question 7

Why are 4-stroke engines better than 2-stroke engines?

Answer 7

1. Efficient gas exchange and cleaner combustion.
2. Better power-to-weight ratio.
3. Compact design.
4. Isochronous operation (constant RPM).
5. Ideal for auxiliary/ small-medium sized engines and Controllable Pitch Propellers.
6. Suitable for generating electricity

Question 8

What factors influence the optimal frequency of hull cleaning?

Answer 8

1. Climate’s effect on hull fouling.
2. Vessel speed.
3. Type of paint.

Question 9

What is the impact of resistance on hull cleaning?

Answer 9

Increased resistance raises fuel consumption, making optimal cleaning frequency critical for savings.

Question 10

What are the limitations/challenges of hull cleaning?

Answer 10

1. Determining optimal frequency is complex (e.g., 2 vs. 4 cleanings in 5 years).

Eqn: Net saving = Fuel Saving (Gross)- (Diver’s cost + offhire cost( stay longer at port to do cleaning)+ speeding up fuel cost( unplanned cleaning, need speed up to next port)

Balancing fuel savings against:
a. Diver costs.
b. Off-hire costs during cleaning.
c. Extra fuel consumption for speeding up.

Risk: Ineffective cleaning frequency increases operational costs or fuel consumption.

Question 11

What is the formula for calculating Indicated Horsepower (IHP)?

Answer 11

IHP= RT×V + alllosses, where RT is total resistance and V is speed.

Question 12

What are the four components of total resistance (RT)?

Answer 12

1. Frictional Resistance (RF).
2. Wave Resistance (RW).
3. Viscous Resistance (RV).
4. Additional Pressure Resistance (RB).

Question 13

What is the principle of operation for a purifier?

Answer 13

Centrifugal force separates water and solids from oil. Water is heavier, pushed to the bowl’s boundary.

Question 14

How can purifier efficiency be improved?

Answer 14

1. Maintain temperature at ~98°C.
2. Reduce throughput for better separation.

Question 15

What are the key stability requirements for dry docking?

Answer 15

1. Adequate GM (metacentric height).
2. Vessel must be upright.
3. Small/moderate trim aft for gradual keel contact.

Question 16

Why is dry docking required?

Answer 16

To maintain operational status, inspect structural integrity, and fulfil SOLAS requirements which is to have two bottom inspection in every 5 years

Question 17

How does slow steaming save fuel?

Answer 17

Principle:
Reduces fuel consumption (proportional to speed²).
Slower speeds mean fewer emissions but longer voyages.

Net Savings Calculation:
Fuel saved − (Extra charter hire for longer voyage).
Use slow steaming only when charter hire costs are low relative to fuel prices.

Question 18

What are the three main maintenance philosophies? List Pros and cons of Each.

Answer 18

1. Breakdown Maintenance: Use equipment until failure.
   Pro: Full usage of machinery lifespan.
   Con: Risk of unexpected failures during operation.
2. Planned Maintenance: Replace parts periodically.
   Pro: Prevents in-service breakdowns.
   Con: Sacrifices some residual life.
3. Condition-Based Maintenance (CBM): Monitor and replace parts based on condition.
   Pro: Optimizes lifespan.
   Con: Expensive due to sensors and systems, increasing initial CAPEX.

Question 19

What are the functions of ballast water?

Answer 19

1. Increases Stability
   - Ensures the ship remains upright, especially in rough seas.
2. Balances Unequal Cargo Distribution
   - Adjusts weight to maintain stability when cargo is unevenly loaded.
3. Adjusts Trim
   - Sets the ship’s floating position by head/bow for optimal navigation.
4. Corrects List
   - Prevents the ship from tilting sideways, keeping it level.
5. Minimizes Structural Stresses:
   - Reduces shear forces, bending moments, and torsion:
6. Prevents Overloading of Stress Limits
   Ensure shear forces, bending moments and torsion below 100% capacity.

Question 20

What are the 3 structural stresses that affects a ship?

Answer 20

1. Shear Force: Opposing parallel forces that could break the structure.
2. Bending Moment: Hull bending caused by uneven forces.
3. Torsion: Twisting of the hull that can lead to cracks. ( more prone in container ships as vessel is always filled with cargo)