Key Takeaways & Executive Findings
- •• The paper proposes a time-domain comprehensive assessment method for Minimum Propulsion Power (MPP) that includes supplementary course-keeping ability criteria, offering higher accuracy and more realistic manoeuvre behavior description compared to existing IMO guidelines. • Comparative analyses with a power line method and two steady-state equilibrium methods reveal that different MPP assessment methods have varying advantages and complexity, forming a multi-level assessment framework. • Key influence factors such as wave direction range and self-propulsion factors at low speeds significantly affect MPP assessment results; expanding wave direction sets stricter requirements, while using low-speed self-propulsion factors reduces unnecessary conservatism. • The time-domain method is particularly useful for ships that cannot meet other assessments or when additional course-keeping ability is required, providing a solution for borderline or unconventional vessels.
Abstract
Currently, the International Maritime Organization (IMO) has approved and implemented the assessment requirement for Minimum Propulsion Power (MPP) of ships in adverse sea conditions. The assessment method and relevant influence factors will have a vital impact on ship's design and operation. On the other hand, MPP is essentially a criterion for manoeuvring safety at actual seas. However, the practical assessment methods adopted in IMO guidelines do not directly and accurately account for ship's course-keeping ability in severe seas. A time-domain comprehensive method with supplementary course-keeping ability criteria has been proposed in the authors' preliminary research. Based on an updated mathematical model and criteria, this paper presents more detailed elaborations, results and discussions on the time-domain method, including the comparative analyses with a power line method and two steady-state equilibrium methods based on IMO guidelines and draft. Discussions on the influences of key factors, involving criterion conditions and calculation parameters, are also presented. The results indicate that different methods exhibit varying advantages and complexity in MPP assessment, thus constituting a multi-level assessment framework for MPP. In particular, the time-domain comprehensive assessment has a higher accuracy with more realistic description of manoeuvre behaviors, capable of offering a solution for the ships that cannot meet other assessments, or for the assessment requiring additional course-keeping ability. Furthermore, an expanded range of wave direction sets a stricter but potentially necessary requirement, while using the self-propulsion factors at low speeds can eliminate the unnecessary conservation of assessment result caused by those at design speed.
1. Introduction
Reducing installed power is the most effective and straightforward way to comply with the mandatory regulation of Energy Efficiency Design Index (EEDI). However, this raises the concerns about unfavorable influences on manoeuvrability with navigational risks for low-powered ships. On this background, the concept and demand of Minimum Propulsion Power (MPP) to maintain manoeuvrability in adverse conditions have been proposed by the International Maritime Organization (IMO). Originally in 2013, the interim guidelines [1] were released for checking the installed power of large- and medium-sized transport vessels, with the adoption of both the level-1 assessment through a minimum power line, and the level-2 simplified assessment using a longitudinal single-degree-of-freedom (1DOF) steady-state equilibrium equation.
Over the years, several research findings and proposals regarding the amendments of the interim guidelines were submitted to IMO, including the definitions of adverse conditions and speed requirement, as well as the determination methods of added wave resistance and self-propulsion factors at extremely low speed. By 2021, the final revised guidelines [2] had been adopted. In addition, the level-3 comprehensive assessment had ever been proposed by solving three-degree-of-freedom (3DOF) equilibrium equations [3], and the requirement of maximum course deviation was raised at the same time. Nevertheless, it has not been approved in formal guidelines due to its complexity of practical implementation.
The MPP guidelines regulate the manoeuvring safety for newly-built and existing ships, and principally serve for simplified and practicable engineering evaluations. However, they cannot replace performance-based assessments for ships near the acceptance boundaries or for unconventional vessels [4]. It was also pointed out at the 29th International Towing Tank Conference (ITTC) [5] that the ...
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ZHAN Xing-yu, MAO Xiao-fei, LI Ting-qiu (2025). Discussion on Methods and Influence Factors for Minimum Propulsion Power Assessment. SinoTechIntel Verified Research. https://doi.org/10.3969/j.issn.1007-7294.2025.06.004
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Frequently Asked Questions
What is Minimum Propulsion Power (MPP) and why is it important?
Minimum Propulsion Power (MPP) is the minimum power required for a ship to maintain manoeuvrability in adverse sea conditions, as mandated by the International Maritime Organization (IMO). It is important because reducing installed power to meet energy efficiency regulations can compromise ship safety, and MPP ensures that ships retain sufficient power for safe navigation in rough seas.
What are the existing methods for MPP assessment according to IMO guidelines?
The IMO guidelines provide two main levels of assessment: Level 1 uses a minimum power line, and Level 2 uses a simplified longitudinal single-degree-of-freedom (1DOF) steady-state equilibrium equation. A Level 3 comprehensive assessment using 3DOF equilibrium equations has been proposed but not yet adopted due to complexity.
How does the proposed time-domain method improve MPP assessment?
The proposed time-domain method incorporates supplementary course-keeping ability criteria, providing a more realistic description of manoeuvre behaviors in severe seas. It offers higher accuracy and can be used for ships that fail other assessments or when additional course-keeping ability is required, thus serving as a comprehensive assessment tool.
What key factors influence MPP assessment results?
Key factors include the range of wave directions considered and the choice of self-propulsion factors (at design speed vs. low speeds). Expanding the wave direction range sets stricter requirements, while using self-propulsion factors at low speeds can reduce unnecessary conservatism in the assessment results.
Why is the time-domain method not yet part of official IMO guidelines?
The time-domain method is more complex and computationally intensive compared to simplified methods, making it less practical for routine engineering evaluations. However, it is valuable for ships near acceptance boundaries or unconventional vessels, and it can be used as a supplementary assessment when other methods are insufficient.
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