Originally Posted by andrewoliv
I am considering re-powering my boat (Mariner 28). The option of converting to an electric drive (Elco) is very appealing. However, I would like to hear from anyone who has an electric drive on their boat. Pro's and Con's.
I am concerned about power into a strong headwind or current. How well does solar or wind re-charge the batteries. Length of time is also a factor.
I cruise the Chesapeake so don't plan to run the motor for 8-10 hours straight. But what is a realistic length of time to run the motor at a comfortable cruising speed? 5-6 knots on a boat that displaces 7500 lbs?
Any opinion welcome
Getting back to the original poster's questions asking for experiences of those who converted...
1) Can an electric motor power a 7500 lbs boat into a strong headwind or current?
Yes, it will. Remember the Queen Mary, submarines, other large vessels are driven by electric motors. The propeller doesn't "know" what is turning the shaft.
2) How well does solar or wind recharge the batteries?
Solar and wind are variable power sources. If the battery is used just to maneuver in and out of the harbor, very little of the potential battery energy is used AND will be better replenished by solar or wind than bulk charging from a diesel/gas engine's alternator/generator. This would happen within one or two days - very acceptable for most day/weekend sailers.
Bulk charging brings the battery capacity back up to 80% of full charge. A "smart" charger is needed to bring a battery back up to 100% of full charge.
If the batteries are discharged very low, an alternate source or recharging would be needed. Or if you have a long enough period of time between uses, the deeply discharged batteries can be recharged by solar and wind.
3) How long can one "motor"?
Most are sized to run maximum speed for typically 2 hours maximum.
In my setup, it draws 120 amps at full speed (just under 6 knots - hull speed). Decreasing the speed to 4 knots, it draws 20 amps. If motor-sailing, I can go 5 knots and draw 10 amps or less. In very light winds, I set the draw to 10 amps. Motor-sailing creates more apparent wind. 10 amp draw out of a 225 amp battery bank gives me almost a full day of motoring. Since we go out for only 6-8 hours, we rarely have depleted the battery past the 50% level - the goal to make the battery last for 6-8 years.
Most of us do have schedules to meet. Each individual needs to factor that into the individual's decision making.
Playing the devil's advocate, I notice that most people are quick to turn on the motor rather than use/develop sailing skills.
I have found that since I now sail with a limited amount of engine energy, I save its use until I really need it. I also have become more adept at sailing, aware of currents, tides, and winds.
Remember, until only a century ago, only wind and muscles powered boats - even on the Chesapeake... Just a thought!