Page:Self-righting boat design.pdf/13

 ;6. Discussion and Conclusions Analysis of the stability of a vessel based on the righting lever arm over the entire range of angles of heel, the GZ curve, has its limits. It is unable to model effects such as parametric rolling, or surf riding and broaching, and the technique has to be extended if it is to include the effects of heave accelerations on the righting moment and the impact of a wave waterline on the behavior of the vessel. However, despite such limitations it is valuable model of many aspects of the behavior of a vessel, and as such a powerful tool that has long been used to evaluate the sufficiency of the stability of all types of craft.

Since the theory of static stability was first elaborated in the 18th century there has been continual research to further understand the complexities and intricacies of this fascinating area of study. Much of empirical knowledge of the stability behavior of crafts is only now being studied in a rigorous way as it is recognized that events that are common for such craft are rare behavior of ships in abnormal conditions. However, the study of vessels such as lifeboats and rescue craft when rolled to very large angles of heel, passed 90° and right up to the completely inverted condition, is unlikely to be applied to larger vessels. This will probably remain area of interest and concern only to those who go to sea in, or design, the smallest of craft. But for such craft the designer must only consider stability under routine operating conditions, but also under the extreme conditions of capsize, which while unlikely cannot be considered impossible.

The stability criteria for such vessels should not only be concerned with normal conditions, and with preventing capsize, but should also provide guidance on the required behavior if capsizing should occur. In addition to criteria based on minimum safety requirements additional objectives based on maximum acceptable accelerations could be defined in the form of a static stability envelope.

There are three main self-righting methods examined in this study. These are; inherent self-righting method, inflatable bag method, and moveable ballast method. All of them have their advantages and disadvantages. Inflatable bag is easy to apply and maintenance, but there are very small area of applicability and does not ensure safety of the crew. Moveable ballast method practically applicable only for small vessel and maintenance of mechanical components is hard. On the other hand, it can design as self-operating system and decent alternative for buoyant superstructure is not feasible. As for the inherent self-righting method, it is the most viable method within the others. Because, there is no working part to go wrong. Although designing inherently self-righting craft is challenging due to the difficulty of weight distribution’s uncertainty during the design process, it is the best option for any self-righting vessel.

It is recognized that the concept of self-righting craft design is practically new concept and largely applicable to small crafts, technological developments and recent researches are promising for future development of self-righting stability.
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