KGmax Curves Associated With Second Generation Intact Stability Criteria for Different Types of Ships

Currently, second generation intact stability criteria are being developed and evaluated by the International Maritime Organization(IMO). In this paper, we briefly present levels 1 and 2 assessment methods for the criteria of pure loss of stability and parametric roll failure modes. Subsequently, we show the KG_(max) curves associated with these criteria. We compute these curves for five different types of ships and compare them with the curves embodied in the current regulations. The results show that the safety margin ensured by the first level-1 method of calculation for both pure loss of stability and parametric roll seems to be excessive in many cases. They also show that the KG_(max) given by the second level-1 method and by the level-2 method may be very similar. In some cases, the level-2 method can be more conservative than the second level-1 method, which is unanticipated by the future regulation. The KG_(max) curves associated with parametric roll confirm that the C11 container ship is vulnerable to this failure mode. The computation of the second check coefficient of parametric roll level 2(C2) for all possible values of KG reveals the existence of both authorized and restricted areas on the surface formed by both the draft and KG, which may replace the classical KG_(max) curves. In consequence, it is not sufficient to check that C2 is lower than the maximum authorized value(R_(PR0)) for a fixed ship's loading condition.

Stability of a tumblehome hull under the dead ship condition

Some methods for direct stability assessment under the dead ship condition were currently developed by the international maritime organization （IMO） under the Second Generation Intact Stability Criteria. Model tests and simulations are carried out to validate the numerical methods used in assessing the stability under the dead ship condition. This is done in three stages. Firstly, the uncoupled roll mathematical model （1 DOF） is adopted to calculate the roll motion based on the irregular beam waves and the steady wind. Secondly, a drift free experiment is conducted to measure the roll motion under irregular beam waves with zero speed, and then two restrained experiments with counter weights and four springs are performed under the same condition. Finally, the effects of the drift and sway motions on stability under the dead ship condition are then verified by experimental results, and the results of the numerical methods are compared to the results of the model experiments. It is concluded that more accurate numerical methods could be developed for assessing the direct stability under the dead ship condition.