We've got one of those Nordhavns with dry exhaust. Like everything, there are tradeoffs.
Pro's:
- No raw water system, so no impeller, no seawater heat exchanger, and no water injection elbow. Also no seawater after-cooler if so equipped. These are big plusses in terms of maintenance and things that can break and potentially cause significant engine damage.
- No soot on and around the transom, swim platform, etc.
Con's:
- The stack takes up measurable interior space on the boat.
- You need to cover the stack when not in use, or have a stack top with integral water trap.
- Soot is a hassle, as are hot exhaust gasses. The instruments at the top of my stack are covered in soot, and when the wind is behind me, my outside temp gauge reads 120-150F from the exhaust being blown forward. Some of this could have been mitigated by better placement of instruments had I thought about this in advance. We also get some amount of soot on the boat deck and dinghy, but not real bad.
In all honesty I think it's a toss. And not all Nordhavns are dry exhaust - not even close. I believe all twin engine boats are wet exhaust, and quite a few singles too. My rough guess would be that 25-30% of the fleet is wet exhaust, perhaps more.