Given heel and trim, either one of these commands 
completes the specification of the waterplane. 

Depth and Draft are the same when heel and trim 
are zero and no special draft line has been defined.

For Depth, think of a diver's pressure gauge calibrated 
to show water depth. In GHS, Depth usually means 
"Origin Depth"; that is, the distance up from the origin 
(of the coordinate system) to the waterplane.

On the other hand, Draft depends on where it is measured.
By default, GHS assumes that Draft is the distance from 
baseline to the waterplane at the location of the LCF. 

Whereas Depth is taken perpendicular to the waterplane, 
Draft is taken perpendicuar to the baseplane.