When this boat was assembled in the late 90's there had yet to be developed a way of adapting a transmission to a turbine. So these were direct-coupled to the drives. He cut a well in the back and mounted this outboard in the middle of the tunnel. When you wanted to back up, you lowered the outboard and started it.
In order to shift the transmissions on turbines, brakes were developed to momentarily stop the output shaft rotation. A turbine at minimum idle RPM still has a turning output shaft. And not all turbines are capable of having the output stage stopped- even briefly. That may have been the case with the units he used here. I can't remember what they were. The owner had an old Cig 35 for sale about 10 years ago that I looked at. I checked out the Cougar while I was there.