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50 Y.A. SOYADI, Y.A. SOYADI, Y.A. SOYADI ve Y.A. SOYADI

 Ballast can be used to enhance upright stability.
 Disadvantages of ballast transfer method include:
 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

Determining the buoyancy locations are vital on any self-righting vessel design. For methods
like inflatable bad 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.

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.

4.1 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.

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

GiDB|DERGi Sayı 6, 2016