Having discussed the basics of intact stability of surface ships, we are now at a stage to analyze the same. Passionate about marine design, he believes in the importance of sharing maritime technical knowhow among industry personnel and students.
Normally, the centre of gravity will be on the centreline in a properly trimmed boat, but it can be persuaded to move further from B to give a marked enhancement on the righting lever.
As a result of the negative righting lever GZ , the ship heels further upto an angle where the righting moment and righting lever, both, become zero. The vertical position of centre of gravity G of the ship is not always fixed. First Time Atlantic Crossing.
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However, as long as a condition of loll prevails, the equilibrium condition will not be achieved when the ship is upright. The only unknown in the above expression is the value of KN. One of the most commonly occurring ones is the free surface effect. Crossing an Ocean. Artwork by Andrew Simpson. Sea anchors and drogues for storm conditions.Ship Stability _ Cross Curves of Stability_ Introduction to GZ & KN curves
It's clear that hull form has a significant effect on stability. Though the values traced by the curve may be different in each case of loading, but the shape or curvature of the curve will hardly change, because it depends on the geometry of the hull.
Our eBooks: But both the ships would respond very differently due to the initial curvature of their GZ curves. The location of G is fixed, unlike B which changes as the boat heels and the immersed section changes shape. What's New! The Gz curve illustrates the relationship between the three key factors that determine the boat's static stability: It may so occur that the initial metacentric height of the ship becomes negative.
How to Recognise a Sailing Fanatic... The value of KN at each angle of heel is then replaced in the expression above, to obtain the GZ at each angle of heel. In fact, a ship designer or an officer on-board should be able to know the stability characteristics of a ship just by looking at the curves.
When such a GZ curve is obtained during design phase, the designer must iterate the design of the hull.