Electric Sport boats are the most common type of boat amongst casual hobbyists. Hobby quality boat speed generally start at around 20MPH and go up from there, and can be just as fast or faster than their internal combustion counterparts, with the latest in Lithium Polymer and Brushless motor technology. Ready to run speed boats from AquaCraft, ProBoat and OffshoreElectrics can reach speeds over 40mph out of the box and with modifications can reach well into the 50-60mph range. These types of boats are referred to as “hobby grade” and can be found only at hobby shops and retailers. “Toy grade” boats which are obtained through mass consumer retailers, are generally much slower and their maximum speeds are usually less than 15MPH.
Scale boats are replicas of full-size boats. They can be small enough to fit into your hand, or large, trailer-transported models weighing hundreds of pounds. More often than not they are a miniaturized version of a prototype, built using plans and/or photos, although there are variants that utilize freelance designs. An offshoot of this style of marine RC’s is radio-controlled submarines.
Reference: Wikipedia Radio-Controlled Boat