Join Date: Feb 2012
Location: Northern & Southern California
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The above reply is well thought out and quite true. There are many scenarios that by the type of use by the operator your efficiency goes up. Example, your boat is inland on a narrow waterway and you always have to motor to get to the good sailing area, so say 10 miles motoring for a nice full day of sailing and then returning those 10 miles to your slip. Total, 20 miles using the motor but zero fuel consumption because during the first part of sailing you were regen, letting the energy captured in the sails top off the charge of the batteries. At the end of the day your on shore power.
Now for the cruiser, you let the low pressure system pass before starting on your next passage, so the winds have abated but the sea state still has those huge swells. Your not a fan of deploying a drogue, and with electric propulsion you don't have to. With the wind speed and direction, you figure to average say 8.5 kts (you have a light cat), so you set motor revs for that speed. As you climb a swell, instead of losing speed, energy is pulled from the batteries and you maintain speed. On the back side of the swell, instead of picking up speed with the chance of pitch poling, your speed is kept in check and your returning electrons back into the battery. My friends that have this system silently motor-sail most the time, allowing predictable ETAs to anchorage.
While on the hook, your solar is adequate to provide your needs even with an electric galley, but for two weeks you have been a very social animal (again, your on a cat) and have entertained guests most every night. The batteries are at 70% DOD, and you decide instead of running the gen-set, you'll just enjoy a day sail instead and top off the batteries.
So, I admit, with the up and down conversions, efficiency is lower, but the flexibilty of the system allows you to reclaim lost efficiency and then some.
WL7GS Whiskey Lima 7 Gone Sailing
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Last edited by deckofficer; 03-01-2012 at 11:57 AM.