Hi John.. Methinks that you can replace the 4hp with a smaller 4 stroke, but it depends on the sailing that you do. You didn't mention where you sail, if there's strong wind/tides that you need to motor against, etc. I've powered Stargazer with a 36 pound thrust trolling motor while I was getting the 8hp Evinrude repaired. The former owner sailed out of Ft. Myers, Fla., in the Gulf, and probably needed the 8hp when the tide was wrong. I sail on Lake Lanier, Ga., and use a 3hp Seagull. Some wind at times, but no current to motor against. Unless you do a lot of motoring, I'd forego the alternator. It won't give the battery much of a charge for the few minutes one usually motors to get out of the slip/ launching area into the wind. Harvey/ Ga M-17 Stargazer #294