[macojoe]

My guess is that he is asking you what shaft leanth you need?? Which is the top of transom (center) to bottom of the boat.
Or from the motor bracket were it sits on the transom to the Cavatation plate (above prop)
This will give him the shaft leanth of the motor.

I hope this is it?? other wise yopu will need some one wiser then I!!

I have never heard of that measure before?? you can change the distance from boat to prop by timming the motor??
When you find out let us no, as I have never heardof this before and I converted my boat to a outboard motor and never considered this??
But it works fine.