# Cs & av values of RINA

Discussion in 'Boat Design' started by Aegwynn, Dec 17, 2016.

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### AegwynnJunior Member

Hello there, i am a yacht design student and currently working on my 27m alluminium hull motor yacht which is my master thesis.
I am about to calculate my bottom pressures and i can't figure out what are the Cs and av values that i need to input for the p2 value which is : P2 = 15*(1+av)*(W/(L*Cs))*g*FL*F1*Fa

Cs is explained as "Support contour of the yacht, in m, defined as the transverse distance, measured along the hull, from the chines to 0.5L. For twin full yachts, Cs is twice the distance measured along the single hull." which is incomprehensible.

av is explained as : maximum design value of vertical acceleration,
in g, at the transverse section considered

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### TANSLSenior Member

Cs is the distance "1 + 1" (see picture), measured along the shell of the hull.
For multihulls, you need to measured one hull and multiplied by the number of equal hulls.
"av" is a variable that varies along the length of the boat. At some point in the regulation you are using you can find the formula that gives you the value of "av" for the area of the boat you are considering.

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3. Joined: Dec 2016
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### AegwynnJunior Member

Thank you good sir!, its impossible to find those things online I will look for av more deeply in Rina then.

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It is in Part B, Chapter 1, sec 5:

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### AegwynnJunior Member

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### AegwynnJunior Member

Forgot to ask, is this to be calculated only on 0.5L or for only frame?

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### TANSLSenior Member

Cs : just for the Main Section, usually at 0.5 Lbp from after perpendicular.
av : for every area of the ship you are calculating. As you can see on Ad Hoc's picture, it varies with x/L

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### AegwynnJunior Member

Thank you and merry christmas !

9. Joined: Sep 2011
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### TANSLSenior Member

You're welcome. I'm at your disposal if I can help with anything else.
I wish the same for you.

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