Hi all,

I am doing some calculations using API RP 2A WSD and I am having some doubts when determining the hydrostatic head (Ref. 6.2.5.2 22nd ed. or Ref. 3.2.5a 21st ed.).

Hz is a function of some paremeters including z and d.

z - depth bellow still water surface including tide
d - still water depth


I am a bit confused about the difference between these two.

If someone could clarify me it would be highly apreciated.

Thank you!