Operational Strategies for CII Under Short Voyages: Hybrid Denominator Correction and CPP Mode Optimization

This study addresses structural distortions in the IMO Carbon Intensity Indicator (CII) for short-voyage training vessels and proposes corrective strategies combining denominator adjustments with controllable pitch propeller (CPP) mode optimization. Using 2024 operational data from a training ship, we computed monthly and annual CII values, identifying significant inflation when time-at-sea fractions are low due to extensive port stays. Two correction methods were evaluated: a hybrid denominator approach converting port-stay CO₂ to equivalent distance, and a Braidotti functional correction. CPP operating maps for Combination and Fixed modes revealed a crossover point at approximately 12 knots (~50% engine load), where Combination mode shows superior efficiency at low speeds and Fixed mode at higher speeds. The hybrid correction effectively stabilized CII values across varying operational conditions, while speed-band CPP optimization provided additional reductions. Results demonstrate that combining optimized CPP mode selection with hybrid CII correction achieves compliance with required standards, attaining a B rating. The integrated framework offers practical solutions for CII management in short-voyage operations, addressing regulatory fairness while improving operational efficiency for training vessels and similar ship types.