Well, I must say that most Americans think the greater horse power the better. This is a false hood. I have an Amphibi-Con 25 which weighs 4000 pounds and a 6 HP merc single cylindar four stroke pushes it at hull speed at one third throttle. I also have an S & S Crusader which weighs in at almost 20,000 pounds (rolled steel hull) and accoding to my naval architect it can only use 10 HP at the prop. With a 2 to 1 gearing that means only 20 HP engine is needed (she has a 29 HP Mercedes diesel). My Oday 26 has a 6 HP Yanmar diesel which is fine for its 4000 pounds. A 16 footer should be fine with an electric trolling motor. However, the use of the boat is really the governing factor. Possibly a 1 HP Honda would be a better bet if you plan on motoring a lot or if you are in a windy area and need more umph to hold in a cross wind. But then again, sailboats don't do that very well no matter how many horses are working.