# Stability of object

#### foo9008

You're getting confused here.

We're talking about the stability of this platform. The center of pressure, etc. has no bearing on this analysis.

The location of the metacenter M depends on the inertia of the waterplane cut by the hull of the platform. Using b = 0.3 would make no sense, since this dimension represents the depth of the platform's hull.

The Ixx used in the equation for yp represents something else and is not applicable here.

For the stability of this platform, BM = I / V, but I can be calculated about an axis which either runs parallel to the length of the platform or parallel to the breadth of the platform, which ever choice leads to the least value of I. V = volume of displacement and remains the same in any event.
thanks for pointing out that i mixed up the Ixx in the equation of center of pressure with the second moment of inertia of MB

#### foo9008

You're getting confused here.

We're talking about the stability of this platform. The center of pressure, etc. has no bearing on this analysis.

The location of the metacenter M depends on the inertia of the waterplane cut by the hull of the platform. Using b = 0.3 would make no sense, since this dimension represents the depth of the platform's hull.

The Ixx used in the equation for yp represents something else and is not applicable here.

For the stability of this platform, BM = I / V, but I can be calculated about an axis which either runs parallel to the length of the platform or parallel to the breadth of the platform, which ever choice leads to the least value of I. V = volume of displacement and remains the same in any event.
the platform has 6 faces ( 3 different types) of surface , how do we determine which surfaces should to consider into the calculation ?

#### SteamKing

Staff Emeritus
Homework Helper
the platform has 6 faces ( 3 different types) of surface , how do we determine which surfaces should to consider into the calculation ?
You want to consider the surfaces which cut through the water when the platform is floating. The waterplane thus created will be parallel and coincident with the surface of the water. It is the moment of inertia of this waterplane which is the key parameter in determining the value of the distance BM.

#### SteamKing

Staff Emeritus
Homework Helper
The image below shows the appearance of the waterplane of a vessel with the traditional pointy end:

The waterplane of this pontoon is somewhat simpler.​

#### foo9008

You want to consider the surfaces which cut through the water when the platform is floating. The waterplane thus created will be parallel and coincident with the surface of the water. It is the moment of inertia of this waterplane which is the key parameter in determining the value of the distance BM.
what do you mean by cut thru the water ? when the object is floating , the bottom part will surely sink into the water , whereas the other 4 surface planes is partly submerged with water . so, IMO , there are 5 planes will cut thru water

edit : i think i understand with the previous diagram .

"Stability of object"

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