Siemens has been outfitting big naval and commercial vessels with diesel electric power for years. Its yacht systems arm only recently began addressing the sub-megawatt market, the recreational end populated by many smaller vessels such as the April K, a 48-ft cruiser out of St. Pete Beach, FL.
The reason for the delay was mainly technological, according to Product Manager, Thomas Orberger. The company had to wait for semiconductors to achieve sufficient power density to make an inverter small enough and powerful enough to fit in a pleasure craft. Now that it's here, the system promises boat owners better fuel use, more maneuverability in close quarters, and greater space on board. Paul Smith, owner of the April K, says she's much quieter from the bridge, too.
Smith replaced his vessel's two Caterpillar V-8s with a single 210-hp Cummins diesel engine, which now couples to the Siemens generator. Electricity produced there runs through two Siemens inverters then to a pair of variable speed drives, which power the twin synchronous ac motors and screws.
According to Orberger, the inverter acts as a rectifier too, rectifying all ac inputs—from the main generator, the auxiliary generator, or shore power—to create a common grid. The electricity is then dispatched in the form needed: single phase ac for the hotel loads, three phase ac for propulsion, and dc for the batteries.
According to Smith, he could maneuver the boat at the dock on shore power alone. With the room he gained by losing one engine, Smith added stabilizers, a water purifier, a freezer, and a washer/dryer. He's also been able to go to bigger props with "noticeable" increases in pitch, because he now has "fully customizable torque to the propeller."
The single diesel engine, together with a smaller auxiliary generator, lets the yacht dispense with a second main engine, dispelling an argument that boaters have hashed over for years: whether two engines are better than one. With direct drive engines, a second power plant added reserve capacity to get a boat home. With the Siemens system, a boat with a disabled main engine can still return to port on the auxiliary generator. And the reverse is true, Smith adds: "I can run my air conditioner off the main engine."
The commercial system was first used in diesel-electric buses, Orberger says. "We've moved it from there into marine system and cranes," he says.
The system offers completely integrated power management, which communicates via SAE CANbus protocol to an HMI on the bridge. There, Smith can display engine rpm, temp, torque, hours, and so on, almost like a commercial vessel.
Safety remains paramount. If the computer malfunctions, hard wiring of the inverter gives Smith "get-home capability."
Visit the Siemens Yacht Systems site for configuration information.