Excessive acceleration simplified Operational Guidance

Abstract

Excessive acceleration criterion, developed by the International Maritime Organization within the Second Generation Intact Stability Criteria, deals with lateral accelerations experienced by people onboard. Level 2 criterion considers the ship at zero speed in beam waves, neglects diffraction and gives the expressions for the Froude-Krylov roll moment. In this paper, the Level 2 procedure is generalized for any ship speed and heading by developing the expressions for the Froude-Krylov exciting roll moment as a function of the heading angle and introducing a variance preserving transformation from encounter to wave frequency. The proposed procedure can be easily implemented in a user's code to assess the simplified Operational Guidance without the use of commercial software. The proposed expression is validated comparing the Froude-Krylov roll moment with the one obtained by the 3-D potential code HydroStar®, referring to a barge and a bulk carrier. The bulk carrier is selected as test case to develop the simplified Operational Guidance according to the proposed procedure. A polar diagram representation is chosen to identify safe combinations of ship speeds and heading while a tabular representation is proposed for a given heading to identify the minimum ship speed to avoid large lateral accelerations, for the sea states reported in standard wave scatter table.

Keywords

• Excessive acceleration
• Second generation intact stability criteria
• Operational guidance
• Effective wave slope coefficient
• Froude-Krylov roll moment