Yes it is straight down from the cl of the crank to the edge of the transom. Not to the bottom of the vee.

I was not sure, so this could easily be correct.

when i was working with gellner to determine drive heights / prop size among other things i was instructed to lower the dives to a neautrual position - perpindicular to the transom and then determine from the front side of the dirve where the center of the prop shaft is and then measure staight upward to the point where you meet the V. this is the measurement he was looking for anyway. it was difficult to my measurements came in somewhere between 11 to 12". don't remember off hand and am not at the shop. i would imagine this measurement would be affected by both the true X dim. and also the degree of the hull bottom. dean seemed to think my drive heights were on the high side however the boat pops out of the water effortlessly with out much slipage.

regardless i am always up for any new knowledge on the issue.

"X" dimension is the distance "on" the transome from the intersection of the boat bottom and transom ( drive location) to crank center to place the prop shafts at the desired heights.
This "X" dimension ends up being the "measurement" as you have to draw a line extending your running surface and then measure straight down from the crank centerline until the two lines intersect. "X-dimension" and "Prop-shaft height" are not the same thing.

Center line to prop shaft center line when trimmed parallel with the extended hull keel line and measured at right angle to that keel line. (not along the slanted transom) Prop shaft height (which is the dimension that most prop builders want to know in order to set you up with the right prop) is the distance, again measured at right angle, from the extended hull keel line to prop shaft center line, and again trimmed parallel. Don't make me come up there....

LOL... why not come up here the weather is awesome. summer is finally here. it's been in the 80's for over the last 3 weeks now. i know what your getting at when you say parallel. i have obtained basically the same results by doing it a little differently. however you have explained how to obtain these measurements very well. this will go down in my boat bible.

so what does it mean when someone says they have an aggressive X dim.?

well said , I will have do one this spring taking a use twin and making it a single, but it will have a DEAN GELLNER 572 in it and konrad drive. or if I hit the lotto have Dean build a twin motor then I would need a bigger boat by a few ft. art

Maybe I am misunderstanding what some of you are saying, but the "correct" definition of "X" dimension is the dimension "on the boat transom" from the bottom to the crankshaft centerline location. It refers back to simple right angle trig, looking for the hypotenuse of a right triangle, commonly referred to as "X" in the formulas. When you look at an X dimension chart, you input your desired propshaft dimension from bottom and your transom angle relative to bottom and the chart will give you the dimension to help place the cutout in the boat to get the desired propshaft location.
Now that is the technical definition, but many, including myself, interchange x for propshaft position relative to the bottom.

Sorry for the late post! I forgot to look at the second page of postings and "Velocity Vector" already put in the correct definition!

This can come in handy when trying to measure your X or your propshaft depth since it can be "awkward" especially by yourself.

Measure to the bottom of the transom assy and add 9.25" and that is your X. Now subtract your X from 21.825" and that will be your prophaft depth.

Example:

From the bottom of my boat to the transom plate is 7.875". Add 9.25" to that to get an X of 17.125". Subtract that from 21.825" to get 4.7" propshaft depth.