Originally Posted by dabnis
If your boat doesn't have a well and you are in choppy conditions I would think you would need the longest shaft that will fit. I had many different 2 stroke engines and they were very reliable and lighter than the present 4 strokes. Our 6HP 4 stroke Tohatsu weighs about 60 lbs, very close to what our 15HP 2 stroke weighed, IIRC. I can only speak from my experience with a Coronado 25 on SF Bay. We could have lived with the 6HP but in addition to sailing on the Bay We made a lot of LONG trips out into the open ocean for salmon fishing. For a slight weight gain we had more than twice the power going from 6HP to 15HP. As mentioned earlier, 9.9HP probably would have been OK
You could try the 6HP 4 stroke or look for a good used 9.9 HP 2 stroke. I would assume most of the used motors in your area are fresh water only motors. You might try a search for an Irwin 25 users group for more input.
Good input. I would definitely look at going with an extra long or long shaft. My last boat had an inboard OMC Sail drive. This was never something I had to think about.