What about the couplings, shafts and props?

Composite couplings. The couplings heart are made of kevlar wrapped in hard rubber. They tolerate up to 3° angulation for any missalignment and they absorb vibrations. They electricaly insulate the hull from the engines as well. This system provide a very smooth ride and are maintnance free. The company is here, look for Hexaflex couplings.

Oil Shafts. The carbon steel shafts are supported by different levels of neddle bearings in an oil bath. There is no water involved at any stage, so the shafts can be freeze in winter without maintnance. Less friction, less noise, optimized trust. They are specially made for the boat, so there is no internet reference.

The propellers are made of a bronze alloy and have 5 blades to lower noise and vibrations (here some exemples). This choice have been made to compromise the following: mid-range power use, vibration free, silence, reduced diameter for shallow water operations. It has been said that Propellers are an art, not a science.