What is the absolute pressure at a depth of 17 msw (56 fsw)?

To determine the absolute pressure at a depth of 17 meters of seawater (msw), it is important to consider both the atmospheric pressure at the surface and the pressure exerted by the water column above. Atmospheric pressure at the surface is approximately 1 atmosphere (ata), which is equivalent to about 101.3 kPa or 14.7 psi.

When submerged underwater, the pressure increases due to the weight of the water above. The pressure increase in seawater is roughly 1 ata for every 10 meters of depth. Therefore, at a depth of 17 msw, the calculation for absolute pressure is as follows:

1. Add 1 ata for the atmospheric pressure at the surface.
2. Then add the pressure increase from the water column. Since 17 meters is just slightly over 10 meters, you can estimate this as:
   • For the first 10 meters: +1 ata
   • For the next 7 meters: +0.7 ata (since every 10 meters adds 1 ata, 7 meters adds about 0.7 ata)

Combining these: 1 ata (surface pressure) + 1 ata (first 10 meters) + 0.7 ata (next