I think you need 200 hp so you can tow the Dallas Cowboys Cheerleading squad on slalom skis!!!!
First, the MD2 is a mid 20hp engine. Had one in my Westsail 32. The westsail had the displacement
of a 40 footer and pushed us along quite well. It is an adequate engine for that displacement
but barely. We're sailors and it worked fine for us while sipping diesel
. We wanted an engine to get us in and out of the slip and power when there was no wind
. It would give us an easy 5 knot cruise
at about a 1/2 gallon an hour in light wind
conditions. We were overpropped so don't know what the max speed would have been but could get 6 k if we wanted to push it. When we had to go in the opposite direction as a strong wind, we motor
sailed at 20-30 degrees off the relative wind but that almost never happened.
The cruising world seems to be populated with powerboaters who have a sailboat. They turn on the engine when speed drops below 5 knots and expect to power into a hurricane
. If that's your style of voyaging go with something huge in the engine department. Might be interesting waterskiing the Cowboy's cheerleaders. If you are going to rely on the engine to save your bacon from dumb maneuvers and want hullspeed cruise
in light conditions, an engine in the 35-40hp should suffice. If you are a sailor, the MD2 should work just fine.
You didn't mention the displacement of the boat. If it's pushing past 30,000 lbs, you might add 10hp to the above reccomendations.