# Question about First intercept for checking Intact Stability

Discussion in 'Stability' started by Phieuduxd, Jul 4, 2016.

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### PhieuduxdNew Member

Dear All,
How to calculate First Intercept Angle in Righting Arm and Heeling Arm Curves (see attached figure).
Thanks,
Phieu

2. Joined: Sep 2011
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### TANSLSenior Member

Assuming you have no more calculation tools, and only the graph you show us, the first thing you should do is to point in the coordinate axes the angles of heel (X axis) and GZ values (Y axis).
That done, with a ruler to measure you take measurements of each of the coordinates of the intersection point and interpolate.

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### PhieuduxdNew Member

Thanks for your answer my question. Good day TANSL.

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### RabahSenior Member

Hi Phieuduxd,
The problem is posed without one very important improvement: Whence is this schedule?
In effect it is Fig1-Righting Arm and Heeling Arm Curves for Area of the Residual dynamic stability /criteria 5.v/ from ABS Rules - Steel vessels under 90 m in length - 2011, Part 5, Chapter 8 Vessels intended for Towing, Appendix 1: Intact Stability Guidelines for Towing Vessels.
See publication by Niru from Philippines: <http://www.boatdesign.net/forums/stability/abs-rules-vessel-intended-towing-operations-stability-55835.html> - attached file.
In this respect Niru is very correct.
After improvement for what criterion and under what rules there is the speech then the answer is the following:
1. If to apply a computer program for calculation of the Intact Stability /approximately GHS, Maxsurf Stability, Delftship Professional, Orca3D or other/ after input of data requiring in the program, the computer itself traces diagrams and receives intersection points of Righting Arm and Heeling Arm Curves.
2. If to use obsolete graph-analytic method, referred to as the Krylov -Dargnies method, after obtaining righting arms and drawing the Righting lever curve, it is necessary to drawing in too scale and the Heeling Arm Curve which is calculated according to Part 5, Chapter 8, Appendix 1, point 9 - Heeling Arm Curve.
_________________________
NA Razmik Baharyan

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### PhieuduxdNew Member

I got it. Thanks so much Rabah.

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