46 C.F.R. § 154.407
Cargo tank internal pressure head.
(a) For the calculation required under § 154.406(a)(1) and (b), the internal pressure head (heq), must be determined from the following formula:
heq = 10 Po + (hgd)max
where: hgd (the value of internal pressure, in meters of fresh water, resulting from the combined effects of gravity and dynamic accelerations of a full tank) = aβ Zβ Y; where: aβ = dimensionless acceleration relative to the acceleration of gravity resulting from gravitational and dynamic loads in the β direction (see figure 1); Zβ = largest liquid height (m) above the point where the pressure is to be determined in the β direction (see figure 2); Y = maximum specific weight of the cargo (t/m 3) at the design temperature.
- (b) The (hgd) max is determined for the β direction, on the ellipse in Figure 1, which gives the maximum value for hgd.
- (c) When the longitudinal acceleration is considered in addition to the vertical transverse acceleration, an ellipsoid must be used in the calculations instead of the ellipse contained in Figure 1.