Answer
1. Indicators of Hull Fouling
Hull fouling increases the frictional resistance of the vessel as it moves through the water, effectively making the ship "heavier" to push.
Performance Shift: The operating point moves upward and to the left of the design propeller curve. You will notice that to maintain a target service speed, you require significantly higher engine power (kW) and fuel consumption than the original sea trial data indicates.
Gradual Trend: Hull fouling is typically a gradual process. You will observe a slow, steady increase in fuel consumption and a consistent drop in vessel speed over several months as marine growth accumulates on the hull surface.
Engine Load: The engine will operate at a higher Mean Effective Pressure (MEP) for a given RPM, trending toward the "Heavy Propeller Curve" shown on your layout diagram.
2. Indicators of Propeller Fouling
Propeller fouling or damage involves physical obstructions, marine growth, or mechanical damage directly on the propeller blades, which alters the hydrodynamic efficiency of the blades themselves.
Performance Shift: The shift is often more sudden or severe compared to general hull fouling. Because the propeller's efficiency is compromised, it fails to absorb the power correctly, often resulting in an immediate increase in torque for a given RPM.
Vibration and Torque: Propeller fouling often introduces abnormal vibrations or fluctuations in torque, which are not typically associated with smooth hull fouling.
Operating Limits: If the fouling is severe enough to push the operating point toward Line 4 (Torque/Speed Limit) or Line 5 (MEP Limit) of your engine layout diagram, the engine may reach its thermal limits before achieving the required power for the desired speed. This poses a high risk of exceeding exhaust gas temperature limits.