Fast electric

Fast electric is a term used in the model boat community to refer to a model powerboat that is powered by a battery instead of a glow fuel-burning two-stroke engine.
The international body "Naviga" defines racing classes for Fast Electrics outside the USA, these classes being broadly divided by drive system (and hence racing format) and number of cells used in the drive battery. Racing bodies in the USA have their own racing classes based on the concept of "sprint" racing over a fixed number of laps, as opposed to Naviga's classes which are based on a fixed time.
*Surface Drive classes race in a clockwise direction around a simple oval course.
*Submerged Drive classes race on an "M" shaped course in an anti-clockwise direction. Surface Drive classes are further sub-divided by hull type, i.e., hydroplane and monohull.
Fast electric powerboats regularly race at speeds in excess of 50 miles per hour, with the current (16-01-2007) world speed record for a fast electric model powerboat standing at approximately 140 miles per hour.
Hardware
Large Fast electric boats over 2 feet in length tend to use surface piercing props.
The prop shaft is almost horizontal with only a few degrees of down angle. This reduces wet drag of the shaft and ensures that most of the thrust goes to push the boat forward.
Because water is 600 times more dense than air, it is not practical to attach a long thin aircraft type propeller to a boat's prop shaft due to material strength and other factors (e.g. "prop walk"). Larger props, however, are more efficient overall, and having the top blades of a surface piercing prop spinning in the air reduces load.
Lithium-polymer batteries have replaced NIMH cells and brushless motors have replaced brushed ones.
To counter "prop walk", dagger like fins and rudders are placed in strategic locations to counter the tendency of the prop to paddle wheel the boat sideways. The faster a prop turns the greater the prop walk, and this effect along with torque roll with single motor setups has to be carefully dialed out.

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