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SELF-RIGHTING BOAT DESIGN 51

conditions. Differences need to be taken into account, because real life sea conditions could not
properly modelled. It is basically up to the designer’s skills.

For vessels that operating in rough sea conditions such as search and rescue boats, prediction of
characteristic behavior of the vessel is crucial. Cost of prototype is considerably high for rescue
vessels, so before executing prototype it is essential to see how ship will handle severe sea
conditions. Dynamic model testing is the method for estimating that behavior.

Traditional towing tank experiments are very similar to dynamic model testing method. In
towing tank test, non-powered hull is pull in the water. Even so, it is a good way to examine
bow wetness, model does not expose to any other wave headings.

Dynamic model testing carried out with self-propelled model in open sea environment. Unlike
towing tank experiments, this time model experience several wave heading at once. Although
superstructure of model geometrically not as important as it was in static model testing, in order
to protect propulsion system, superstructure should be watertight. Also, superstructure weight
should distribute as in real design. Then the model can be directed to encounter waves from all
headings considering capsize, broach and knock-down.

4.2 Computer Modelling and Analysis

With the recent technological development computer programs are fairly helpful to a Naval

Architect for stability analyze in early design process. Modelling software enables to test

different effective hull forms and superstructure geometry. In order to properly model a

self-righting craft, software must be able to analyze 180 degrees of roll to starboard and 180

degrees of roll to port. Additionally, software should manage asymmetrical superstructure

geometry computation like many rescue boats have in their design. Also, modelling the true

shape of design is critically important since any buoyancy location have large impact on self-

righting ability on the vessel. Buoyancy sections that are not included on main superstructure

body such as mast volume also should be computed on that software.

Computation of weight and centers are standard practice for any ship design. But, weight and
weight distribution have utmost importance in any self-righting craft. Even a slight change in
weight or weight centers could cause negative GZ curve. Computer software should calculate
these weight centers on high accuracy. Any increase in Vertical center of gravity (VCG), also
could change the stability curve and cause negative righting levers. Naval architect should have
always checked and updated weight calculations as design and construction progress.

When construction is finished, an inclining test is carried out to determine the accurate center of
gravity and verify the calculations.

5. Design Criteria

In general, design and outfit requirements for self-righting vessels differ little from those of
conventional craft of similar size and function. There are, however, a few areas requiring special
consideration.

Sayı 6, 2016 GiDB|DERGi