Numéro : 2793 - Year : 2023
Statistical analysis of errors due to wind during a stability experiment
Jean-François LEGUEN, Jean-Yves BILLARD, François GRINNAERT, DGA Techniques Hydrodynamiques - IRENAV/Ecole navale, IRENAV/ENSM, France
During the stability experiment heeling moments are applied to a ship to determine the position of its center of gravity, a problem always delicate when you are interested in a ship.
This measure is marred by errors linked both to the knowledge of the hydrostatics of the ship as well as to the employed measuring devices. These errors have been studied and have given rise to several publications. An important element is the influence of the wind during the test and few work have been devoted to this aspect which is evacuated during the tests by the establishment of a maximum acceptable wind fixed arbitrarily at 10 knots.
The uncertainty linked to wind fluctuations is determined on the one hand from the equations of hydrostatic, which make it possible to give an analytical expression of couples applied by mass displacement during experience, and on the other hand from wind, the average value of which is known but whose fluctuations are random and known only from a statistical point of view.
By imposing a desired uncertainty on the measurement of the position of the center of gravity, it is then possible to define a maximum acceptable wind which depends on the characteristics of the ship at the time of the test and the precision imposed. The calculations made show that this maximum wind can significantly deviate from the ten nodes imposed today.
A validation of the proposed calculation is carried out by a Monte-Carlo simulation of the stability experience on several ships.
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