Abstract

The only formal stability-related requirement referring to a turning maneuver of a ship results from the IS Code
and its application is limited to passenger ships only. The goal of the adopted criterion is to prevent an excessive
angle of heel in turn. Likewise, the remaining prescriptive criteria, this one is simply based on the concept of
a threshold that must not be exceeded. In this case, the angle of heel should remain below 10 degrees. The heel
evaluation is based on a straightforward static moments balance model, which is obtained with the use of GZ
curve, without consideration of any dynamic effects. At the same time, according to COLREG convention, a
ship collision evasive action typically consists of the turn to starboard, occasionally even quite hard turn, if
necessary. Thus, the ship heel in turns is unavoidable and the dynamics-related component adds up to the static
one, potentially resulting in excessive asymmetric dynamic heeling. Such a maneuver, if undertaken rapidly,
may be risky since its aftermath might be serious which is revealed by accidents evidence, e.g., the disaster of
Sewol ferry in 2014 with the death toll stood at 294.
Inspired by the SGISC philosophy we conducted the first stage of investigation on determination of the
dynamic angle of heel in turns, with the view on a potential future extension of the list of stability failures
covered by the SGISC. A series of ship motion simulations was carried out in order to identify whether the
simple GZ-based criterion may be found adequate. The simulations accounted for both the maneuverability
and stability characteristics of a sample ship. The up-to-date 6DoF ship dynamics model was utilized to enable
covering major deficiencies of the possibly oversimplified static approach. The contemporary IS Code
recommended criterion outcome for a large passenger ship was compared to the results of numerous
simulations performed for turns in calm water. A proposal of the criterion modification that has been submitted
in 2013 in the document SDC 1/14/1 was included for the comparison as well. The main intended objective of
this article is to initiate a discussion on the possible future modification of the stability during turning criterion.
This issue is pretty much in line with the ship design process but all the more relevant to day-to-day navigation
since collision avoidance, and thus turning at high speed, is unavoidable in the course of a routine operation.

Authors (4)