August 27, 2025
ClassNK researchers have identified a hidden source of fuel waste and engine wear in rough seas that shipping companies may be overlooking: a persistent “speed gap” between commanded and actual main engine speeds.
As explained, when engine orders exceed what the engine can realistically achieve under heavy weather, the governor injects excess fuel in an attempt to close the gap, leading to inefficient combustion. This mismatch, while recognized by engineers, had not previously been quantified in terms of fuel loss and maintenance impact.
ClassNK’s study shows that fuel waste can reach 10–12% during severe conditions, with some trade routes, such as US East Coast–Europe, potentially losing over 114 metric tons of fuel annually, equivalent to more than US $70,000 at current prices.
Credit: ClassNK
Even with speed reduction strategies in place, if the commanded engine speed remains higher than what the main engine can realistically achieve under current weather conditions, the governor will continue injecting excess fuel in an attempt to close the gap without success
… explained lead researcher Dr. Yuzhong Song.
The issue arises because main engines have torque limits, or Maximum Attainable Main Engine Speed (MAMES), enforced by the fuel rack limiter. Setting speed commands above this threshold triggers unnecessary fuel injection without achieving higher propulsion.
Beyond the financial loss, this overfueling can drop the air-fuel ratio, causing incomplete combustion, soot fouling on turbocharger components, vibration, and long-term wear that increases the risk of turbocharger failure.
Credit: ClassNK
ClassNK’s solution is straightforward: monitor the engine speed gap in real-time and reduce commanded speed until the mismatch disappears. Incorporating this practice into voyage planning and crew training can prevent both fuel waste and mechanical damage.
With carbon-neutral fuels remaining far more expensive than conventional HFO, eliminating inefficiencies like speed gaps will be critical for both decarbonization and commercial performance.
