# ISO 12215-5 - Calculation of P-BMD

Discussion in 'Class Societies' started by ClarkT, Feb 28, 2012.

1. Joined: Jun 2003
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### ClarkTSenior Member

I'm using the ISO rules for the first time and working through my calculation of bottom pressure - P-BM

Am I correct in my understanding that I should end with two bottom pressures, one using k-AR for plate, and a second using k-AR for stiffeners? Then I should move forward using P-BMplate for plates and using P-BMstiff for stiffeners and girders?

OR

Should I be moving ahead with one maximum k-AR after calculating k-AR(planing), k-AR(plate displacement), and k-AR(stiffener displacement)?

2. Joined: Oct 2008
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k-(AR) is proportional to k(R) & A(D)

k(R) is a function of its location and ostensibly its speed....displacement mode/planing mode etc.

A(D) has limits in its applicability for "plating" and "stiffeners". Thus A(D) requires a value of "plate" and another for "stiffener".

So, yes, you end up with 2 pressures, one for "plate" and one for "stiffeners". You can save yourself time by working out which yields the greater pressure and use that for both. Unless you wish to work out the pressure for both for each location.

3. Joined: Jun 2003
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### ClarkTSenior Member

Thank you! As it works out for this boat, the planing pressure is dominant anyway, and that is the same for plate or stiffeners.

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