Tank Calibration allows you to determine the properties of the tanks you have defined in the Compartment window, at a range of capacities.

Select Tank Calibrations from the Analysis Type option in the Analysis menu or toolbar.

§   Tank definitions and boundaries

§   Permeability

§   Fluid type

All required Tank Calibration Analysis input can be specified in the Compartment Definition table.

Also see:

Relative Density of Tank Fluids on page 49

§   Trim, fixed trim

§   Hog and Sag (if any)

§   Density

In the Window | Graphs menu each tank can be selected for display in the Graph window. For more information see Chapter 5 Hydromax Reference.

If the vessel is trimmed, there are ranges of tank volumes that will show the same sounding/ullage. (The same effect can occur if the sounding pipe does not reach the lowest or highest point in the tank – remember that this can change as the vessel trims, which is effectively what is happening in the figures below). These points occur when the tank is near empty or near full, see below (increasing the trim, will exacerbate this phenomenon):

Figure a shows a sounding pipe that extends the whole height of the tank, with the vessel at zero trim. Here all tank filling levels will have a valid sounding.

Figure b shows the vessel with (bow down) trim and a small amount of fluid in the tank. Here there will be a range of tank filling levels which all show zero sounding.

Figure c shows the vessel with the same trim, but with the tank nearly full. Here there will be a range of tank filling levels that all show maximum sounding.

These effects will be noted in the tank calibration results if they are extreme enough since Hydromax always adds calibrations at 1%, 97.9%, 98% and 100% full; if the 1% level does not intersect the sounding pipe, the sounding will be given as zero. Similarly if the 97.9%, 98% and 100% full levels do not intersect the sounding pipe, the maximum sounding will be displayed, see below. In the results out lined in red, there are four results which all have a sounding of 1.0m but different capacities – the fluid levels are all above the top of the sounding pipe. In the blue results, the last two results are below the bottom of the sounding pipe, giving soundings of 0.0m but different capacities (the last but one calibration point is the fluid remaining in the tank when the sounding is 0.0m).

  
Tank calibrations for severely trimmed vessels; sounding pipe does not cover full range of tank capacities. The profile view of the tank in the trimmed vessel is shown on the right; the sounding pipe is in the middle of the tank and extends from the bottom to the top of the tank.

In a similar way, if the sounding pipe extends above or below the maximum and minimum fluid levels, you will get readings which have the same capacity but different soundings.

With the addition of user specified tank calibration intervals, it is possible to specify the calibration intervals that you require. These will start at a sounding of zero (rather than an ullage of zero). Note that in addition to the specified soundings, levels of 1%, 97.9%, 98% and 100% full will also be added if they have not already been included in the specified soundings. The 97.9% and 98% levels are given because it is at 98% that the free surface moment is made zero.