The first pic that Green has posted, does show a 'Schottel' drive unit at the left of the plan, no wonder he is confused.

The plan at the top of the thread shows a specific Water Tractor tug plan specifically designed for the VS drives, including the large straight keel at the stern. I suggest Green72West should either use VS drives or use another type of hull for Schottel drives.

Hi Gerd, it's not my plan!
The plan is from 'green72west' who started this thread and seems to be confusing Schottel and Voith-Schneider. Either that or he wants to use two Z-Drives instead of the Voith drives. His intention is not clear. Either way he doesn't need to cut chunks out of the keel, that's nuts😲
Cheers, Doug 😎

Hi Doug
Your plan show a Voith-Schneider-Propeller

Hi Haig, seems to be a common mistake to get Schottel Drives (Z-Drives) and Voith - Schneider confused with one another!
First two pics show a twin Voith propeller on a tug hull (as on the plan above) and the operating principle.
3rd pic is cross section of the Z-Drive as produced by the Schottel company. it is a 360° rotating 'pod'.
Newer versions have electric motors built into the pod and don't need the mechanical Z transmission from inside the hull.
With such pods under bow and stern even bow and stern side thrusters are redundant 😊 4th pic is the Graupner version, Mk II.
https://www.graupner.com/Schottel-Drive-II-new-version-/2335/
Cheers, Doug 😎

Why do you need Schottel drives? The Voith Schneider drives in that configuration can move the boat in any direction? Schottel drives will require fairly big penetrations through the hull, and apart from the installation complications, should (in my opinion) be unnecessary.
This is a link to a fairly comprehensive brochure with photos of the real thing that will help in understanding the concept etc. http://www.gemimanevrasi.com/Tug_Boat_Technology/Voith%20Water%20Tractor.pdf

Bauer- Voith-Schneider-Propeller
https://www.bauer-modelle.com/Voith-Schneider-Propeller-VSP-65BM-mit-Brushlessmotor