Ouzo runs a 140 Suzuki 4 stroke on his 20' Seafari and it is a nice setup. We've gone out and fished all day for 12 hours and only burned about 30 gallons.
Considering that his Seafari is heavier than the MA, and filled with a lot more stuff, I think you would be fine with the 115.
If worse comes to worse, you can always add NITROUS.
