Hull coefficient

[Mirko]

I've been designing a hull for my thesis, starting from the ship lines of another ship. I've already changed the CB shifting the stations, now I have to change the CP. I took a look in my ship design book, and the procedure to change the CP need to shift still the station. Working in this way does the CB change?

Do you know some way to change the CP without change the CB?

THANKS!

[Genjuro]

Supposing you can't change your principal dimensions (L,B,T) and your displacement, you must change your Master Section area in order to reach the required Cp.

Doing this you lose some volume amidship that must be redistributed in the longitudinal direction to maintain the Cb constant, without changing the properties mentioned above.

By changing the M.S. area you change the Master Section Coef. (Cms),that is Cms = Cb/Cp. The result will be a new Centre of Buoyancy as the submerged volume changes.

[Bruno Mattoso]

So knowing that:

Cp = V/LBP x Am

where:

LBP: Lenght Between Perpendiculars
Am: midship section
V: underwater volume.

You can change your LBP( I've never heard about it,but I think it is possible) ... without change your Cb, because Cb's formula is:

Cb = V /LxBxd

L: the lenght of the waterplane

[Genjuro]

Mr. Mattoso,

You won't be able to change the LBP and keep the same Cb without losing displaced volume. If you lose volume, you lose buoyancy, so you won't have the same cargo capacity anymore.

[Mirko]

I thought about this problem, I realized that if I want to change the coefficient of the midship section I have to change its shape, but in this way the hull won't streamlined anymore.

It's clears that the three coefficients CB, CM, CP have to satisfy the following formula:

CB=CM*CP

what do you think if I shifted the waterlines to obtain my CM, and if I shifted the stations to obtain my CB?

[masrapido]

If your lines are already streamlined and you like them, the only way to get the centres as close as possible is to shift the weight around. Or get the new shape.