Hybrid electric drive for small craft

The Navy's small craft spend the majority of their operating hours at either idle or full power. The form of hybrid drive proposed for the 7-meter RHIB is tailored to these operating characteristics while preserving present speed and range capabilities.This type of drive is characterized as a parallel hybrid drive with a large engine and small battery. Other Naval ships and craft may warrant other hybrid electric drive train choices.We have specifically postulated a need for a low-speed (5 knot) range of 10 miles under electric propulsion. We have sized the battery pack at 12 kilowatt hours to provide the required speed and endurance with a 20% margin for wind and wave effects. Theproposed battery is a Lithium Ion high-energy pack, includes a thermal and charge management system, and is packaged in a composite container with a total weight of 135 kilograms.Fuel savings are achieved in the present design by operating at low speeds over modest distances without the engine. Low speed operation of the engine is the least efficient part of the engine's operating envelope and significant fuel is burned at theselow speeds. Signature implications of this operating mode are obvious. A more efficient propulsion system that will lead to lower operating costs of the 7-meter RHIB. Mission capabilities can be expanded with the silent mode of operation.