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SELF-RIGHTING BOAT DESIGN 53

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 [8].

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.

References

[1] Stefan Grochowalski, 1989. Investigation into the Physics of Ship Capsizing by
Combined Captive and Free-Running Model Tests. SNAME Transactions Vol.97, 169-
212

Sayı 6, 2016 GiDB|DERGi