After watching "the last ship" on TV I started wondering........
The standard DDG-51 class can go 4,400 nautical miles at 20 knots
I was wondering with a 16% fuel saving with Hybrid.....how far will a hybrid equipped DDG-51 go on service turbine-generators at 15 knots ????
Right now, DDG-51 destroyers are fielded with a ship service electrical system, and an independent main propulsion system of LM2500 gas turbines that are tied to a mechanical drive through the Main Reduction Gear assembly. Each shaft is tied to 2 LM2500 gas turbines (GTMs), which have just 2 speeds: off, and on. Another 3 ship service turbine-generators (GTGs) provide electrical power, with the 3rd designed as a redundant back-up. Using this mechanical arrangement, current DDG-51 Flight IIA ships have a reported total power output of 7.5 MW, and end up using too much effort from their LM2500 gas turbines for propulsion at low speeds.
During underway operations under 15 knots, in low-threat areas, 2 engines are typically on line: a gas turbine GTM with a trail shaft, and a smaller ship service turbine-generators GTG for basic power to the ship, navigation radars etc. Speed changes up to 15-18 knots are controlled by varying propeller pitch, and are independent of the LM2500 GTM. For more electricity, another GTG generator can be brought online to power the main SPY-1 radar if needed.
At low speeds, Hybrid Electric Drives would allow ships to take the gas turbines GTM offline, and rely on 1-2 smaller service turbine-generators GTGs for both propulsion and power, using less fuel and offering more power flexibility. Ships could also be designed with fixed-pitch propellers, which are quieter than variable-pitch blades. As a bonus, Hybrid Electric Drives (HED) propulsion is less noisy, which is useful when a ship is trying to deal with enemy submarines, hybrid electric drive also reduces fuel use and increases range by 16%, cutting each ship’s annual steaming cost by $2.5 million.