My bow thruster is faired quite smooth to the hull. It is also very "finished" on the inside. It is not supported in the middle, as yours also is not, but seems very strong. My opinion is that you should request (a nice way of insisting) that the
interior finish
work be completed to yacht standards. (nice way of letting them know it has to be smooth, color matched and pretty). Yank around on the tube. If it is not rock solid, have them install a strut under the tube. It would be very easy to build one out of
fiberglass. The flange on the outside of the hull....
This is a tough one. 50 mm is a pretty large protrusion. On my boat the build-up is on the inside of the hull, which allows the outside of the hull to be smooth. It actually would be easy to fix, but time consuming.
Epoxy the inside of the hull around the tube, to build up a strong area for bonding. This would have been much easier to grind and fill before the tube went in, but can still be done. Make sure that all
epoxy is bonded to well cleaned, non painted, surfaces - hence the grinding. On my boat this collar is several inches thick. You have to decide is this issue is worth the effort to change.
I agree that having a surveyor look at this installation is a great idea. Also you
broker should be able to help you find other similar boats that have bow thrusters that you can look at. Get your
broker involved, they have a vested interest in your satisfaction - and are usually very happy to help. Don't pay anyone any
money until you are 100% satisfied (or at least hold back a significant amount).
Lastly, congratulations on the new boat! That is so cool!! You're going to love the bow thruster. I don't use mine too often, but when I do, it really adds a level of control that makes maneuvering easier.