I assume you have a 200 hp E rude. Theres several reasons why you may have a 21 p prop. The prop may not be the right style or type, prop may be damaged, engine may have lost some hp since its and older engine, engine height setting, boat heavier than normal meaning there could be water inside the foam. There could be a number of things that may be causing your slower speed when comparing to new modeled boats. Good luck fishing and enjoy the boat!