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Mariner's Formulae Quick reference guide
Hydrostatic Loading
 
HYDROSTATIC PRESSURE
Pressure at any point in a fluid = ρ x g x h [KN/m2]

      where ρ = density of liquid [tonnes/metre3]

                g = 9.81 [metre/second2]

                h = distance of the point from liquid surface [metre]

HYDROSTATIC LOAD
(1)  Load acting on an immersed plate = Pressure x Area
                                                        = (ρ x g x h) x A [KN]

       where ρ = density of liquid [tonnes/metre3]

                 g = 9.81 [metre/second2]

                 h = centroid of the immersed area from liquid surface* [metre]

                 A = immersed area of the plate [metre2]


(2)  Load taken by a stiffener of an immersed plate = ρ x g x h x A [KN]

       where ρ = density of liquid [tonnes/metre3]

                 g = 9.81 [metre/second2]

                 h = centroid of the immersed panel area from liquid surface
                    = depth of immersion of the plate divided by 2 [metre]

                 A = immersed area of the rectangular panel plate supported by
                       the stiffener
                    = width of panel x depth of immersion [metre2]


CENTRE OF PRESSURE
- the point of an immersed plate at which the resultant hydrostatic load acts.
Centre of pressure from liquid surface

    =   2nd moment of area of immersed area about surface
             1st moment of immersed area about surface

    =    I + A(h)2   [metre]
             A(h)

     where   I   =   I NA [metre4]
                     =   2nd moment of area of the immersed area about
                          the neutral axis which is parallel to the liquid surface

                 A  =   immersed area [metre2]

                 h  =   position of the neutral axis from the surface [metre]
                     =   centroid of the immersed area from the liquid surface


CALCULATION OF CENTROID
Centroid of immersed area from liquid surface = Σ (A x y)
                                                                          ΣA

     where Σ(A x y) = Moment of area about liquid surface

                            = (A1.y1 + A2.y2 + A3.y3 + ....)

                        yn = distance of centroid of each immersed area, An
                               from the liquid surface

                       ΣA = total immersed area

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