Adding something heavy like a hardtop, coffin box, generator or bait tank can affect your propeller needs. The prop(s) that pushed the boat just fine before the addition might now leave your engine struggling and burning more fuel than necessary, according to Yamaha's Meeler. To check, make sure the engine(s) revs up to the maximum-rated rpm range at wide-open throttle while underway. If not, step down to a lower pitch and retest. Also, think about a four-blade versus a three-blade prop, Meeler advises. Four-blades often create more lift and less wetted area under the hull. Though boat speed might drop, this also results in less drag and greater efficiency, translating to greater mpd.