X Dim
 

In finding the X Dim on a deep V is it measured from the lowest point of the V to the center of prop shaft?

No, the original definition of the x dimension is the distance from the driveshaft of the motor (input shaft of drive) to the lowest point on the vee.

However because this doesn´t take into account whether a shorty, standard or spacered drive is fitted, most people measure the x dimension as you have described, propshaft to bottom of vee (whether that is pad, or a conventional vee).
On a twin, the relevant dimension is measured from the hull bottom directly in front of the centrleline of the drive, to the propshaft.

On a single, 7"+ (prop to vee) is not unusual on older hulls running 3 blade props, but less than 6" is more common, these days, especially with 4 blade props. Stepped hulls can run higher drives than conventional vees, I believe.
90+ mph boats running 5 or more blades get down below 4".

My 80 mph 26 foot boat has a 4 1/2" drive height (on an extension box) and runs real nice.


The variables of hull design, weight, centre of gravity, prop, intended speed range make it impossible to generalise, too much.