[Innomare]

+ As said, your speed may be higher, because you can fit bigger and slower-turning propellers (with bigger reduction ratio gearbox) with the same propeller tip clearance.
+ Also your shaft angle may be smaller which helps too.


- You will have a cardan shaft which needs replacement at certain intervals (check with supplier).
- If one of the cardanic couplings would ever fail, the spiralling cardan shaft would likely carve a large hole in your engine room bottom.
- You will need to build a protective cover over the cardan shaft.
- As mentioned, weight and cost will be higher.
- The gearbox has to take up the thrust, and this source of noise will be located closer to the accomodation (assuming to be located fwd of the engineroom bulkhead). It's not possible to work with a separate thrustbearing which is a more quiet solution.

Bruno