I developed the following mental conversion methods while attending Submarine Officer Basic Course. They seem so simple-minded, someone must have already developed them. If not already familiar, perhaps some will find them useful.
While riding the Dive Trainer during the Submarine Officer Basic Course, students sometimes focus on one depth indication. The instructors break this bad habit by mating that indicator fail.
In self defense, I developed the following methods of quickly converting Ballast Control Panel (BCP) sea pressure indication in psig to depth (feet) and BCP sea pressure indication in feet to pressure (psig). Both use the 44 psig/100 ft conversion factor as a starting point.
I realize that plastic laminated cheat sheets are taped to BCPs throughout the fleet. However, they may not be visible to the DOOW or the OOD, or they may become misplaced. I prefer to have the option of doing the conversions in my head.
Sea Pressure to Depth Conversion
It is easier to demonstrate this method than to explain it.
Step 1: Read BCP gauge and round off to nearest 10 psig 127 –> 130
BASIS: Simplifies calculations
Step 2: Multiply by 2.5
130×2 = 260
+ 130/2 = 65
BASIS: You take 44 psig/100 ft. and invert it: 1 ft/0.44 psig. Multiply this by 1.1:
1.1 ft/0.44 psig = 1.1ft/(1.1×0.4) psig
= 1 ft/0.40 psig
= 2.S ft/psig
Step 3: Reduce the Step 2 value by 10% (rounded to nearest 10′) and round to nearest 10′:
BASIS: This offsets the 1.1 multiplier in Step 2
If you use the 100 ft/44 psig multiplier directly, you would get a depth of – 290′ for a sea pressure of 127 psig.
On some BCPs, sea pressure is displayed in feet. This gives the DOOW or OOD a convenient check on depth. However, the COW needs sea pressure in psig so he can pressurize AUX-3 or – 4 when using the Depth Control System. It is possible to do the conversion in your head, as follows.
Step 1: Read BCP gauge and round
off to nearest 10 feet 330
Step 2: Divide by 2 165
Step 3: Reduce Step 2 value by 10% 165-16 = 149 c:-150 psig
BASIS: Start with 44 psig/100 ft:
0.44 psig/ft = -0.45 psig/ft
= (112 – (l/10)x(l/2)] psig/ft
If you use the 44#/100′ multiplier directly, you would get a sea pressure of – 145 psig for a depth of 330′. The error is in the conservative direction, because the tank pressure must be greater than sea pressure.