Wednesday, July 6, 2011

Electric Propulsion?

Part of the allure of a sailboat, is the freedom of the wind (well, when there is wind). The low impact on the environment, and enjoying nature without an engine running in the background.   Well in my many travels through the internet (it really is a big place), I've come across a couple references to green sailing, and electric propulsion.  It sounds too good to be true - and probably is.  The engine when running is quiet, but for long cruising you can't really recover enough power without a genset.   But maybe battery technology will improve - I mean seriously, at the rate I'm progressing on my journey we'll probably have transporters before I sail! So below are comments from one of the companies that produces the engines.  Just something to think about.

Just push the throttle and go.

No more grinding the starter,
Or praying the engine will catch,
Or waiting for it to warm up,
Or clunking the gears into forward,
Or ear-shattering noise,
Or obnoxious fumes.

You slide away from the pier in silence - as quietly as under sail. The only sound is water slapping the hull. The only smell is the salt sea air.

It's clean, green, electric sailing. And with oil near $100 a barrel, and environmental regulations increasing, it's the sailing wave of the future.

Energy from batteries:
Batteries deep in the hull provide the energy to move. They've been charged from dockside AC or from onboard solar panels.           

Electrons flow from the batteries through a controller that chops them into pulses. The pulses surge through the motor windings and create fluctuating magnetic fields that silently spin the shaft.      

If headwinds or high seas start to slow the boat down, more electrons automatically flow through the motor. Boat speed stays steady, without operator control.

Regenerative sailing converts renewable energy from the wind to electricity that recharges the battery pack. A rough guide is that three hours of sailing regenerate the electricity from one hour of motoring. But the ratio varies greatly depending on sailing speed, prop size, rate of electrical consumption while motoring, etc.

When the sails go up in open water, you throttle the motor back so it's just ticking over. The motor turns the prop slowly while you sail. It corkscrews through the water and cancels most of the drag. When boat speed increases - from sliding down a wave or the wind picking up - the prop is forced to turn faster as the water rushes by. The motor then becomes a generator and sends electricity back to the batteries.

As you rise up the back of a wave, the ammeter reads negative. The motor is consuming more electricity to maintain speed on the upslope. Heading back down, the ammeter turns positive as the boat speeds up. The motor is regenerating electricity and recharging the batteries. On a windy day, the boat can return to the dock with more power than when it left.

If the wind dies, you push the throttle forward to maintain speed. Apparent wind picks up and keeps the sails pulling. Now you're motorsailing, but still with no noise or diesel smell, and you haven't burned a drop of fuel.

Generator backup:
Eventually the batteries discharge to their preset minimum level. A cocooned diesel generator starts up automatically. From the cockpit, it's barely audible over the wind through the rigging.

The generator runs with maximum efficiency at a constant, optimum speed. It recharges the batteries as the boat continues motoring, and shuts down automatically when they're fully charged.

Quiet nighttimes:
On the hook at night, the air conditioner starts up and runs quietly off the batteries. Depending on their state of charge, the batteries may power the AC through the entire night. If they run down, the cocooned generator automatically starts running quietly to bring them back up. No more getting up in the middle of the night to start a noisy diesel engine to recharge the house batteries.

Maximum control:
Heading back to the dock, the boat is easy to control. The motor can be slowed to single digit rpms, stopped and started repeatedly, and reversed in an instant.

No more wrestling the shift lever from forward to neutral to reverse to forward again. No more heading into a slip too fast with no way to go slower. Collisions with the dock are a thing of the past.

Its all part of clean, green, electric sailing - the sailing wave of the future.

It sounds good, but until the battery technology improves, I don't know if it will appeal to cruisers or not.  This all probably goes against the simpler is better statement that I've been told to follow, but it sure sounds like a neat idea!


  1. Them batteries that drive that neat motor will be made of unobtanium.

    The problem is weight, electrical management and maintenance of those batteries. You never know when you will plug into a miswired marina power source and fry the charger and all those expensive batteries. And those batteries are way more expensive once you leave the Land of the Big PX.

    I would love to have a dc motor for my propulsion needs but the technology and manufacturing base aren't quite yet at the cheaper side. I wonder if you could disassemble a Toyota Prius electrical storage system and reengineer it to fit in a sailboat motor enclosure...? Way too technical for me!

    Until then, diesel is the most practical and dependable method of non-wind propulsion.

    My point is not to bum you out or slow down the dream; If you happen upon some big bucks in the future, you can do anything you like with your boat.

  2. Barco - I just so happen to have a lot of unobtanium ;) Actually, I just posted about those systems because they sounded neat. I will not be in a position to get one, and I don't know that they are really ready for a long-term cruising lifestyle. It will definitely be diesel for me.

  3. I did an *awful* lot of research bout this actually, when looking to repower my 39' sailing trimaran. weight is a serious issue on multihulls, so I was looking to replace a 27-horsepower diesel motor and a 100-liter fuel tank.

    for the same size and weight as the motor and the full fuel tank, I could install a battery-powered motor that could take me at the same throttle for up to three hours. With a full tank of diesel, I can motor for over twelve hours straight! The realities of sailing to a schedule (which isn't the ideal, but often is the reality) is that sometimes you just have to motor into the wind for hours and hours to get where you're going.

    eventually, yes, electric is the future. right now, with the cost of LiFE batteries, it is not the answer for any serious liveaboard cruisers - it's getting to the point where it's a valid option for people motoring out of slips to the bay to sail for a few hours, then motoring back to their slip to plug in for the night - but coming up with a thousand amp-hours of charge when at anchor would take one *hell* of a solar array, or running a Honda EU2000i generator for about 20 hours straight, which isn't really saving you any fuel...

  4. Drew - Yeah, with the reading I did, I came to pretty much the same conclusion. It would be nice though. But for long distance cruising, or being a liveaboard, I guess the technology just isn't there yet. I can't imagine the number of solar panels you'd need to try and charge that sucker if you wanted to get away from a generator. I'm guessing it sounded like a cool solution to you too, since you did an "awful" lot of research.

    Also - I don't hear too much about trimarans on the various forums. What pushed you in that direction? Although I guess I could stop being lazy and just go read your blog (which of course I will because I'm a blogoholic :) ).