Cutting down trolley motor, how to determine proper length?

[jitterbug127]

I have a Minn Kota Power drive trolley motor that has been awesome! I love it. The one problem I've got is that I fish a really shallow river and the shaft for the trolley motor is way too long. I can run it shallow but then it sticks up in the air like 2 and a half feet. It makes casting off the front of the boat very difficult. I've see where they can be cut down. I've also see that its recommended to have a Minn Kota dealer do the work. Im trying to decide how much to get cut off without cutting too much off. Anyone have a good method to determine this? Or is it simply a trial and error thing?

 

[jitterbug127]

I found a good article describing exactly this. Please disregard.