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 Boat Design Forums How to obtain the maximum righting arm of a righting arm curves？

#1
04-12-2016, 01:40 AM
 xichyu Junior Member Join Date: Apr 2016 Rep: 10 Posts: 87 Location: Dalian，Liaoning，China
How to obtain the maximum righting arm of a righting arm curves？

Areas under righting arm curves are carried out using 2nd order integration. Likewise, the
maximum righting arm is determined by a series of predictions and trials based on 2nd order
interpolation.
But I do not know the concrete details
How to obtain the maximum righting arm of a righting arm curves？
#2
04-12-2016, 02:47 AM
 TANSL Senior Member Join Date: Sep 2011 Rep: 300 Posts: 3,893 Location: Spain
For the point of maximum abscissa of a GZ curve [y = f (x)] you need to determine the point to which the first derivative is zero: dy / dx = 0.
This you could get two points. Choose the one that has a positive orderly.
There are other not so simple methods.
#3
04-12-2016, 07:29 PM
 xichyu Junior Member Join Date: Apr 2016 Rep: 10 Posts: 87 Location: Dalian，Liaoning，China
Quote:
 Originally Posted by TANSL For the point of maximum abscissa of a GZ curve [y = f (x)] you need to determine the point to which the first derivative is zero: dy / dx = 0. This you could get two points. Choose the one that has a positive orderly. There are other not so simple methods.
Thanks
#4
04-12-2016, 08:07 PM
 gonzo Senior Member Join Date: Aug 2002 Rep: 2031 Posts: 11,833 Location: Milwaukee, WI
On a cartesian coordinate system, it is the highest point on the curve. Depending of the degree of precision you need, a simple visual inspection may be enough. Even though the maxima of a curve can be calculated easily by integration, most stability curves do not have a precise equation to describe them. Often they are approximated during the design process and later corrected by inclination tests.
__________________
Gonzo
#5
04-12-2016, 09:02 PM
 xichyu Junior Member Join Date: Apr 2016 Rep: 10 Posts: 87 Location: Dalian，Liaoning，China
Quote:
 Originally Posted by gonzo On a cartesian coordinate system, it is the highest point on the curve. Depending of the degree of precision you need, a simple visual inspection may be enough. Even though the maxima of a curve can be calculated easily by integration, most stability curves do not have a precise equation to describe them. Often they are approximated during the design process and later corrected by inclination tests.
In some cases the top is not obvious, may be flat or double humped
#6
04-13-2016, 03:00 AM
 TANSL Senior Member Join Date: Sep 2011 Rep: 300 Posts: 3,893 Location: Spain
Quote:
 Originally Posted by gonzo On a cartesian coordinate system, it is the highest point on the curve.
As stated by the OP, there may be relative maximums that are not so easy to find. It seems that the OP knows better than you what he is talking about.
Quote:
 Originally Posted by gonzo Depending of the degree of precision you need, a simple visual inspection may be enough.
That's something no responsible designer would dare to do.
Quote:
 Originally Posted by gonzo Even though the maxima of a curve can be calculated easily by integration, most stability curves do not have a precise equation to describe them.
The maximum of a curve can not be found by integration. That is nonsense.
All curves, including stability (GZ or DN values) can be defined by a precise mathematical equation, or set of equations.
Quote:
 Originally Posted by gonzo Often they are approximated during the design process and later corrected by inclination tests.
In the design process you calculate several values, which can not be changed with the data obtained from the inclining experiment. When you do experiment long months have passed since you made the project and the boat, of course, is already built.
The project data and curves are not corrected. The stability booklet based on the data of experience is made. But this is a completely different thing and sometimes it is not even the designer who does the experience.
#7
04-13-2016, 07:35 AM
 gonzo Senior Member Join Date: Aug 2002 Rep: 2031 Posts: 11,833 Location: Milwaukee, WI
Designing and calculating graphically has been done for centuries and still is used with success.
__________________
Gonzo
#8
04-13-2016, 08:01 AM
 TANSL Senior Member Join Date: Sep 2011 Rep: 300 Posts: 3,893 Location: Spain
Of course, but that has nothing to do with what you say in your post # 4, which are nothing but totally incorrect statements.
#9
04-13-2016, 10:53 AM
 gonzo Senior Member Join Date: Aug 2002 Rep: 2031 Posts: 11,833 Location: Milwaukee, WI
So you say that the highest point on a curve on a Cartesian coordinate graph is not the maxima?
__________________
Gonzo
#10
04-13-2016, 11:27 AM
 TANSL Senior Member Join Date: Sep 2011 Rep: 300 Posts: 3,893 Location: Spain
No, I did not say that at any time. Do not try to divert attention to another site. Reread what you have written in your post # 4, which are nothing but nonsense, and what I answer in post # 6.
#11
04-13-2016, 01:20 PM
 gonzo Senior Member Join Date: Aug 2002 Rep: 2031 Posts: 11,833 Location: Milwaukee, WI
It says:"On a cartesian coordinate system, it is the highest point on the curve'
How about you stop you bad attitude and insults, stop hi-jacking threads and stick to the subject. Many posters have stopped asking questions because of you.
__________________
Gonzo
#12
04-13-2016, 01:30 PM
 TANSL Senior Member Join Date: Sep 2011 Rep: 300 Posts: 3,893 Location: Spain
That's your opinion and certainly respect it. However, as everything is written, everyone can see that I at any time have insulted you or have sabotaged a thread. I just correct certain things you say that are not right and that show a complete misunderstanding of the issues being addressed. And I think I do it politely.
#13
04-13-2016, 10:52 PM
 PAR Yacht Designer/Builder Join Date: Nov 2003 Rep: 3967 Posts: 17,891 Location: Eustis, FL
I agree TANSL, it seems or at least it appears many of your posts, are to directly attack or correct some minor level of semantics by Gonzo. In fact, it seems or at least appears this is your only contribution to many threads. Additionally, once I see both of your screen names, bounce back and fro in a thread, I stop participating, knowing it will simply descend into a pissing fight over some usually minor mis-statement or observation.

This thread is a classic example. Only 12 posts, 5 by you, 4 by Gonzo and 3 by the OP. All of the OP's posts where in the very first portion of the thread, the rest, your attempts to make observations to Gonzo's posts. I've seen this many times previously and this thread will dissolve into this pissing contest thing and a tit for tat spiral into uselessness, in terms of contributing to this thread.

We all mis-speak from time to time, it happens, but to intentionally seek out or hunt for these, just so you can point out your position or what you feel an appropriate response, particularly against a single forum member, just isn't acceptable behavior. You have a choice which threads to participate in.
#14
04-14-2016, 01:13 AM
 xichyu Junior Member Join Date: Apr 2016 Rep: 10 Posts: 87 Location: Dalian，Liaoning，China
Thanks for all of you！ Sincerely！
#15
04-14-2016, 07:20 AM
 gonzo Senior Member Join Date: Aug 2002 Rep: 2031 Posts: 11,833 Location: Milwaukee, WI
A double humped stability curve is very common. When it has a flat area where the maxima is, the usual graphical solution is to go a fixed distance to the right and left from either side of the flat. Then you pick the center point.
__________________
Gonzo

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