Rod Sumner of Niagara Falls, CAN asks:
Thanks for answer yesterday. Your described system of a hydraulically powered alternator off the main engine seems to have many possible benefits: no fuel lines to AC generator, no cooling water line to be clogged, easier maintenance, less complexity with space and weight requirements, quieter...It would seem that this is a system possibly well suited to smaller boats as well.
One down side is having to run the main engine while at rest to top up the batteries and/or handle short term heavy loads. Comments would be appreciated.
Dan Streech responds:
Rod, thank you for your 3rd series of questions on the hydraulic alternator subject. First, I should say that the hydraulic alternator/inverter package is not a replacement for the stand alone 20kW Northern Lights generator. 8kW just wouldn’t be enough to feed all of the AC needs on a 62 foot boat. It is intended for use using careful power management when the vessel is underway. At anchor or even underway when the AC loads are high, one would use the 20kW NL. A Nordhavn 62 carries enough fuel to run non stop for 25 days or even longer at reduced speeds so the temptation to find a way to harness engine power to make AC power on a continuous basis is quite high.
An operator trick that I haven’t mentioned is the ability to run the hydraulic alternators off of the wing engine. In a typical installation of hydraulics on an N57 or N62, the hydraulic pump for the thruster (or thrusters) is mounted on the wing engine. This is because the engine can advanced to about 2,000 RPM and have ready power for one or both thrusters regardless of the RPM of the main engine. When powering the alternators only from the wing engine, the RPM can be reduced to quite a low (and quiet) level and in this configuration, the wing engine can act as back-up AC generator (via the hydraulic alternator and inverters). I would consider the use of the main engine to power the alternators while at rest to be a last resort after failure of the 20kW NL and failure of the wing engine.
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