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I have a hydraulic drive system on my 50', 25ton schooner. A 72HP John Deere engine drives a hydraulic pump which drives port and starboard motors connected to driveshafts that drive port & starboard propellers. So one engine, two propellers. It gives good maneuverability in marinas (not quite as good as a powerful bow thruster, but much better than a single screw) at the cost of a loss in efficiency.
The system on my boat came out of a fishing boat, and I wasn't the owner who installed it, so I can't directly compare it to other systems. The hydraulic system has it's own water cooler (which tends to last ten years or so), which is fed by the seawater coming off the engine's water cooler.
With the hydraulic system, one still does need to do alignment between the shaft coupling and the hydraulic motor, but presumably you would find that much easier to do because you would be able to mount the hydraulic motor in a place with good access.
The hydraulic motors are not silent, they have a kind of whine noise to them. One could insulate the area around them if the noise was an issue.
The drive system on my boat is probably 30 or so years old. I've owned the boat for 14 years and 60,000 miles. In that time, I've replaced the hydraulic oil cooler twice, all the hoses once (as a preventative measure before an arctic trip where repair facilities would not be available), the oil and filter a few times. A stainless steel oil cooler would be a nice thing to have, but they're not easy to find.
In general, I think of hydraulic systems as simple and reliable.
Feel free to email me if you wish more details or photos. I will have internet access for a few more days, then am sailing across the atlantic, so won't be able to reply later.