statical stability

[azri]

hello i'm from malaysia...i have a few problem regarding stability of the boat hope you guy can help....

can anyone explain to me how to calculate a B (buoyant) point when a ship heel in large angle???


i really appreciate your help tq..

[Ad Hoc]

Hi Azri, welcome

Do you have access to a stability software program? If so, then it is straight forward. If you don't then you'll have to calculate it by hand. If you're doing it by hand, and you're unsure, then a simple Q&A in a forum will not help you. Since you'll need to understand and learn a lot more before you begin with simple stability calculations. In which case give it to a professional naval architect to guide/help you on a one to one basis, in person.

Stability is not difficult, but it requires a lot of previous knowledge to grasp what is required. If you do not have that, your road ahead is very long.

[Ike]

The center of buoyancy is the center of the underwater volume at any heel angle. So first you need to know what the shape of the underwater volume is at a given heel angle.

As Ad Hoc said, if you have access to any hydrostatic software then it is easy. Otherwise you have to take measurements off the drawings and calculate it by hand. That is a long process.

[azri]

tq for your advise Ad Hoc i really appreciate it...actually i have those kind of software facilities....the problem with software is you lose the algorithm behind it.....for your information i still a student study naval architecture in one of our local university....

if to find the (B) point is difficulty, allow me to ask a few more question cause you seen really helpful...

i already try a few formula in NA book but all of them are useless, in the end of the calculation i'm still get the GZ value increase while the theory say other wise...

so what is your suggestion, for me to calculate and generate statical stability chart by hand???

[azri]

Originally Posted by Ike

The center of buoyancy is the center of the underwater volume at any heel angle. So first you need to know what the shape of the underwater volume is at a given heel angle.

As Ad Hoc said, if you have access to any hydrostatic software then it is easy. Otherwise you have to take measurements off the drawings and calculate it by hand. That is a long process.

so you mean i have to Simpson back the shape of underwater volume??? likes calculating original VCG = (product moment volume/product volume) * waterline lever....

[Ad Hoc]

Originally Posted by azri

...actually i have those kind of software facilities....the problem with software is you lose the algorithm behind it...

There is a difference between the computer code (algorithms) and the maths behind the logic of the program.

The computer code is simply that and the realms of computer science not naval architecture, per se.

The logic, for the computer code, is based upon known naval architecture which can be obtained from any text book.

If you have the lines plan of the vessel in question, you can either input the data into one the software programs you note, or as Ike also noted, do it by hand. Take measurements off the lines plan and work out the volumes etc.

Either your gaol is to be a better computer programmer or a naval architect. You need to decide which it is and follow that route.

[Ike]

so you mean i have to Simpson back the shape of underwater volume??? likes calculating original VCG = (product moment volume/product volume) * waterline lever...

That is the general idea, but you do it for the new shape when the boat is heeled. It is a long tedious process but if you have to do it by hand that is the way to start.

[azri]

Originally Posted by Ad Hoc

There is a difference between the computer code (algorithms) and the maths behind the logic of the program.

The computer code is simply that and the realms of computer science not naval architecture, per se.

The logic, for the computer code, is based upon known naval architecture which can be obtained from any text book.

If you have the lines plan of the vessel in question, you can either input the data into one the software programs you note, or as Ike also noted, do it by hand. Take measurements off the lines plan and work out the volumes etc.

Either your gaol is to be a better computer programmer or a naval architect. You need to decide which it is and follow that route.

in may cases the boat volume are still the same (no added weight).....the problem is the volume operate in different angle....

[Ad Hoc]

Originally Posted by azri

..the problem is the volume operate in different angle....

And that is what you have to calculate and establish the effects of such

[azri]

Originally Posted by Ad Hoc

And that is what you have to calculate and establish the effects of such

tq for all the idea...like say it a long process....

i think i know where to start now...

if something i lose in this journey plz guide...

keep in touch....

[Tim B]

Have a look around this site:

http://opendynamics.engineering.selfip.org/

And also at the source code here, particularly lines 43 to 115:

http://opendynamics.cvs.sourceforge.....1&view=markup

Which uses a triangle mesh of the hull, extruded to the undisturbed wave surface to calculate the volume properties of the hull. I now have a full 6 DOF dynamics model based on that theory, but it's not quite ready for it's first commit yet.

Remember also that a boat, when heeled will pitch (and yaw about it's loacl Z axis) as well. This is why we write computer programs to solve it for us!

Tim B.

[azri]

hello again,

i have found wedge method of calculate the problem base on the book principal of naval architecture...so i would like to ask your opinion regarding to this method...

[Tim B]

Let me turn your question around. Under what conditions do you believe that the presented theory is valid? and why?

Tim B.

[azri]

Originally Posted by Tim B

Let me turn your question around. Under what conditions do you believe that the presented theory is valid? and why?

Tim B.

tq for reply....

actually i'm to much loss in the particular topic, before this i'm only experience computer software analysis, now i realize that how important to understand the base....sorry if this is not answer you turning question very well..

i being seek and finding this stability problem for almost 2 week right now until i found this useful forum....in that particular period i have found some interesting concept that sometime i cannot find it in my university structure...

i do believe that the above method valid because the major problem i facing right now is to find new position of (B) that change due to the changing of waterplane area, so the above method consider the centroid of both wedge port side and starboard side and also volume of the wedge that relate to the displacement of the boat...and it also consider the original (B) and (G) is constant....

hope this can answer you question.....

i really appreciate every guided.....

[Ike]

Azri, that method looks ok. You just need to solve for B.