GZ diagram

2021.11.17. - News
GZ diagram

 Photo: Envato Elements

Article from Vilmos Dömel naval architect

In the calculation of the stability diagram we did not take into account the beneficial effect of the immersion volume of the deck houses, due to which we do not have to design scrap waterproof steel doors and windows, but build beautiful wooden doors and windows. The condition for this is that the openings leading to the hull can be closed with watertight steel lids, but these can be hidden.

The ship’s GZ diagram is very reassuring. In a beaufort 6 wind, even when the sail is full, the ship is heeling only 13 degrees, and only then does the edge of the deck sink into the water - this means in strong breeze (22–27 knots) she travels with full sails with water on the deck. This is the static angle. In the case of a gust with a force of B6, the dynamic tilt is roughly double that, which is tolerable.

According to the stability regulations, in order to withstand a dynamic gust of wind, the work of the restoring torque of the hull must be at least 1.4 times the work of the tilting torque of the wind. This is represented by the area under the GZ curve in the image below. This criterion is well met for our ship.

The additional requirements are also met twice: the maximum value of GZ must be at least 0.30 m, in our case 0.62 m; the minimum value of the initial metacentric height must be at least 0.6 m, in our case 1.414 m.

Furthermore, in Beaufort 12 storm the ship must withstand in all circumstances. Magyar would endure even with a full sail, she would heel down to approx. 71.5 degrees, but would not capsize. (An another issue is that there is obviously no crazy man that would maintain a full sail in the B12 wind…).

Later, for each sail variation I calculate in tables the amount of static and dynamic heeling at each Beaufort degree. Then it becomes clear how much sailing a dynamic gust of wind (B12) can withstand.

Most importantly, the range of stability exceeds 90 degrees, and the GZ curve reaches zero value at 92 degrees, thi meaning the ship will capsize there. This is thanks to the 120 tonne ballast. So, by all human calculation, the Magyar will be a good stable ship.


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