[ask]how to get cross curve for this trimaran

[dan41]

Dear all,

I am maritime student from Indonesia, and seeking help from You.
How to caculate stablity from this lines plan to get cross curve?
any suggestion?

[Guillermo]

Are you sure about those (strange) forms? It seems the forward sections are missing.

May I suggest you to run your own curves?
You may use these spreadsheets: http://www.faststability.wiwat.pl/

Cheers.

[dan41]

hmm..i just attached aft sections..

Thx a lot Guillermo,,i'll try the spreadsheets

[dan41]

Guillermo,,

i hav try the spreadsheets, and to make cross curve, it still to insert manually value of KN for each degree.
The problem is im a little bit confused how the get this value from trimaran cos its have tri hulls. I'm using Benyamin and Spence method to get the KN for each degree and volume.

I get confused with Y1 and Y2 for trimaran..which one y1 and which one y2??

Any idea for my problem? or maybe U have another method to get KN for trimaran?

I'm sorry for my bad English,, i hope U can understand what i mean.

[Guillermo]

dan
those spreadsheets are not the right ones for your purpose, I'm sorry.

To find the cross curves for a tri is not different than for any other boat. You have to find the righting arms measured from point K at different heeling angles for a chosen set of displacement values.

You have to fix a chosen displacement (so a draught) and then heel the boat a certain set of angles (let's say 5º, 10º, 15º....175º, 180º) keeping displacement the same (draught will not remain the same. You have to find out by trial and error process), then finding the combined CB position for all three hulls in that position and then measuring the distance from K to the vertical of the CB at that heel angle (point N or point Z depending on notation system). You'll get that way the KN (or KZ) values for each angle for that specific displacement, that you can represent as a vertical line of dots in a diagram where displacements are in the X axis and KN values in the Y axis. Then repeat all process again for several displacements, and finally joining all same heel angle dots with lines, to get the cross curves diagram.

Quite tedious to be worked out by hand, you'd better use a NA software.

Cheers.

[dan41]

Owh,,i see.

Thank you very much guillermo.

[TTS]

I am looking at your design in another manner. May I ask what your goal is with this boat also what is LOA and B-Max?

[dan41]

I got this design from my senior, and now my lecturer order to me to check the stability.

Middle hull's
LOA: 15 m
B: 2.84 m

Side hull's
LOA: 10 m
B: 1.9 m