Page:Self-righting boat design.pdf/10

 *Ballast can be used to enhance upright stability. Disadvantages of ballast transfer method include: Determining the buoyancy locations are vital on any self-righting vessel design. For methods like inflatable badbag [sic] and moveable ballast, there may not much choice. However, when designing an inherently self-righting craft, hull form, superstructure geometry, and distribution of weight play utmost importance. Since, stability data comes late in design process in traditional ship design, naval architect should pay attention to buoyancy locations.
 * High number of mechanical components such as self-operating valves requires maintenance to ensure 100% reliability.
 * Quantity of ballast water might restrict application and size of vessel.
 * Not viable for planning craft where the additional weight would limit performance. Planning craft also have the difficulty of keeping water ballast in the tank whilst under way.
 * Vessel structure must be designed to withstand continuous immersion in seawater. The RNLI Oakley 37 was always kept ashore as incompatible materials used in the ballast tank construction quickly corroded if left afloat (Figs. 4–5).
 * System can result in vessel being recovered in one direction irrespective of capsize.
 * 4. Self-Righting Testing Methods

In today’s technology, computer programs help to realize any mistake made in early design process but in order to avoid repetitive calculations, stability data should be produced carefully.

There are several ways to analysis design’s self-righting ability. Mainly, they could be grouped as, computer modelling and analysis, model testing. Model testing is the most powerful investigation method of any self-righting craft. It is mainly categorized as static model testing and dynamic model testing.
 * 4.1 Model Testing

In static model testing, small models are used to investigate the self-righting behavior of design. Different loading situations are examined to check calculated data. In order to create these situations ballast water and loading cells are used.

In this process, static model must prepare very carefully. Hull form and superstructure geometry should meet to required scaling effects. Model needs to be completely watertight and possess all external features of original design.

In example of search and rescue boats where, self-righting is mostly used, survivors that taken onboard on rough sea conditions change the center of gravity of vessels. This kind of weight changes may not be modelled even on the most powerful engineering software. In this type of situations static model testing is the best reliable method of all self-righting methods. Simulation of capsizing is recorded via video. So, after static model testing completed designers could watch the video on slow motion and determine the real ship’s behavior under those