# moment of inertia

Discussion in 'Boat Design' started by abhishek, Apr 18, 2012.

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### abhishekJunior Member

What is the moment of inertia of a rectangular plate making an angle except right angle or multiple of right angle with it's axis which is passing through the centroid of the plate?

SIR,.

Please help me in this regard, I have a doubt in finding out the moment of inertia (Iown) for bottom plate and side shell plate as the bottom shell is making 18 degree with the base line and the side shell is making 5 degree with the vertical reference line, the sizes are (bottom is 15300mm x 6 mm ) and (side shell is 14250 mm x 6 mm ), suppose if the bottom shell is parallel to base line it is straight to horizontal and not making any angle, it is {(15300) x (6)3 }/ 12 = 275400 mm4 .

If it is side shell {(14250) 3 x (6) }/ 12 = 1.44 x 1012 mm4

But here both the bottom and side shell are not horizontal and vertical.
So I know the formulae should be in sin and cos as they are making some angles.

For bottom shell moment of inertia is :
[{(15300) x (6)3 }/ 12] x cos2 18° + [{(6) x (15300)3 }/ 12] x sin2 18° = 249101.64 mm4

For side shell moment of inertia is:
[{(14250) x (6)3 }/ 12] x cos2 (90-5° )+ [{(6) x (14250)3 }/ 12] x sin2(90- 5°) = 1.435 x 1012
mm4

IS the calculation correct?

Or else could any one solve for me please.
Please find the attached copy of the section .

Last edited: Apr 19, 2012
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### DCockeySenior Member

Student assignment or test?

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