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Old 27-10-2012, 01:44   #1
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Circumnavigating using Electric Propulsion

Hello all,

I've been reading up about Electric Propulsion on these amazing forums and elsewhere. It seems with modern day lithium batteries, solar/wind, etc, we're approaching a point where ditching the old engines might be possible.

Of course it totally depends on your sailing style- Electric Propulsion isn't going to motorsail you for 10 days at a time but it is improving.

My question is this.. Are any of you out there actually using this to cruise around? I've seen huge cats covered in solar panels, but what about "normal" boats. The 40' monohull with 400-600watts of solar on the back and a large lithium bank.

From what I've read such a system would give you maybe a day's solid power at best. Is that going to cut it out there in the real world? Are any of you actually sailing like this and found it to be useable?

I'd LOVE to go down this road when I buy my boat (hopefully soon!) but would also LOVE to hear some real world cases of people that have experience in if the tech is there now, or if I'm dreaming.

Many thanks in Advance,
Simon
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Old 27-10-2012, 01:57   #2
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Re: Circumnavigating using Electric Propulsion.

There is a young adventurer doing this around NZ at the moment. $1000 26ft'er sailed from San Francisco without petrol or diesel. Sails, electric outboard, large homemade paddle. Good bank of batteries with two or three permanent panels and extras stored away for when conditions are right. In the doldrums can sail 3knots all day when the sun is good. Dunno what his diet is like.
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Old 27-10-2012, 05:28   #3
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Re: Circumnavigating using Electric Propulsion.

I think it will be a great option for circumnavigation for a boat that can carry enough solar panels to make it practical. For a keelboat there is limited space, but if some spare panels can be articulated out from the sides when in dead air, you could probably keep moving through the doldrums. There's a group of filmmakers enroute to complete the Great Loop on a solar-only trimaran (no sails, no shore power, no generators...just solar to battery to torqueedos). I posted an article near the beginning of their journey (Waterway Cruising Guide | Cruising Guide News) -- it pretty well outlines some of the limitations, as they have found they can only travel 20-30 miles a day. (The journey is in haitus until the spring...he may take the boat to the Bahamas for the winter).
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Old 27-10-2012, 06:45   #4
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Re: Circumnavigating using Electric Propulsion.

I've been reading up about lithium batteries and they seem to be the way to go. Half the size, double the capacity- and prices are dropping all the time. If you filled a 40' mono with these- keeping in mind the space the fuel tank frees up as well- I think it might be doable.

I think the trick though is to want to SAIL whenever possible. Give this large bank time to recharge. 30-40 miles per day isn't that bad if you ask me.

Si
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Old 27-10-2012, 06:52   #5
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Re: Circumnavigating using Electric Propulsion.

Have been very interested in electric power for boats but my conclusion based on all I could find out about current technology you have several limitations compared to standard diesel power.

1. Battery only, recharged by solar, plug in at a dock or small onboard generator. Great for getting to a from the dock or out a channel to the ocean but unless you fill the entire boat with batteries you have extremely limited range. Even with a huge battery bank once discharged can take a long time or a big charger to recharge so again range is limited.

2. Electric motor to power the boat with a generator large enough to run the motor directly. You can still run under battery only for docking or short distances but have the option to run the generator for extended range. However you are again running a diesel powered engine to run the boat with the added inefficiencies of converting diesel to electric to prop instead of diesel to prop.

3. Current commercially available marine electric drives, if you replace an existing diesel with a similar powered electric it can cost double the price of a new diesel and transmission. If you include a generator to power the electric drive system the cost can be triple.

So for someone that normally sails everywhere and never motors more than a few miles electric may work but still not cheap unless you have a very small boat or very under powered system in a larger boat.
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Old 27-10-2012, 10:28   #6
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Re: Circumnavigating using Electric Propulsion.

It's been covered before, but the problem is energy density and energy demands.

Batteries store nowhere near the power needed to power a boat for any leingth of time, and solar panels cannot provide anywhere close to the power requirements of a reasonably sized vessel's demands for propulsion. Advocates always want the numbers to be better than they are, but simple math, giving the electrical system every possible rounding error and benefit of the doubt just can't get close to the amount of power necessary to provide propulsion.

So just to go through it quickly...

A standard 40' sailboat will have about a 40hp engine installed. Lets assume that for transit purposes we are willing to accept low speed to be much more efficient. So lets say we are willing to limit ourselves to only 10hp. Which would be about idle speed for a 40hp engine. Its pretty minimal for a 40' but let's see what happens...

10hp is the same as 7.45kw or 7,450 watts used per hour. So to power this engine we would need to generate 178,800 watts per day from our solar panels.
But solar only works during daylight, so we have to account for this. Lets be optimistic and say we will get 6 hours of production a day (most installers use 4 as a base line btw), so we will need to generate 29,800 watts an hour over those 6 hours. How large a system does this require...

A nominal 100w panel, well it will generate 100watts an hour... So for our propulsion needs you would need to find space for 298 of them. So what does our array look like...

Well it will weight roughly 7,500lbs not including the framing or brackets and will be 26 feet wide, and 50 foot wide.


Alternatively lets say we want to ignore solar panels, and just use batteries... So how big of a battery bank do we need to power our boat at the same 10hp for a day...

Well again we need 7,450 watts an hour, times 24 hours equals 178,800 watts. So how big of a battery bank does this require? Ignoring inefficiency, 178,800/12v batteries = 14,900 amp hours in batteries for the day.

If we go lithium ion which is the most energy dense battery around right now, you would be looking at about 4,600 pounds in batteries, and a cost of right at $150,000 in battery's.

Instead lets say we go lead acid traction batteries to try and save money... Now we are looking at 14,900amp hours / 210amp hours / battery, or roughly 71 dep cycles 12v batteries at a total weight of 9,300lbs...

Now remember these calculations are assuming 24 hours of run time. But on a very small (relative to the boat) power plant.
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Old 27-10-2012, 10:48   #7
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Re: Circumnavigating using Electric Propulsion.

Check out THE BIANKA LOG BLOG. Mike is a pretty regular poster here on CF and has been using his boat for coastal cruising for something like the last 5 years.
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Old 27-10-2012, 11:22   #8
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Re: Circumnavigating using Electric Propulsion.

You aren't going to do a non-stop circumnavigation, but I think it would be possible. The thing is, you need to build a more efficient boat, that uses less energy to move through the water. Second, you can go 60-80 miles a day, but might have to wait a day or two for the batteries to recharge.

You also have to have have nothing that interferes with the Sun hitting the solar panels. This boat is close and is the size we are talking about: Island Pilot DSe Home Page
Or this one Boat - SolarWave

Lithium Iron Phosphate batteries are very impressive, and a 48V, 800 Ah battery pack wouldn't be too bad at 750 lbs and about $15,000 US. 38,000 watts could run a 5kW motor at full power for 6 hours (keeping the batteries above 20% to have them last longer). You would need at least 2,500 Watts of solar, if not more though. And solar panels are getting better every year.

And that is if you don't have wind turbines or some type of a sail kit to help. And even I would probably have some type of small generator when it comes to open ocean crossing just to help make better time. However, I would like to coastal cruise around most of the world and would be able to wait for good weather windows.

Avoiding storms is the biggest worry I would have.

I wish they made more of these types of boats, and made sure that the propeller design reflects the benefits that electric motors have to operate better at lower energy levels.
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Old 27-10-2012, 11:36   #9
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Re: Circumnavigating using Electric Propulsion.

The stored energy to weight of the power plant ratio and the horsepower output to weight of the power plant ratio is not close to that of the same ratios of petroleum...at least not yet. The technology will need to advance significantly for solar to be on par with petroleum in those respects.

I can certainly understand wanting to get away from petroleum, even if the power and stored energy to propulsion plant weight ratios are much less. I do like that people are experimenting, even if they are making a big show of it. How else do you advance a technology other than experimentation?

When there is a commercial passenger airplane that can cross the country on batteries and solar panels at a competitive speed, then we will know we are there.
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Old 27-10-2012, 13:05   #10
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Re: Circumnavigating using Electric Propulsion.

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When there is a commercial passenger airplane that can cross the country on batteries and solar panels at a competitive speed, then we will know we are there.
He is asking about a boat, not a plane. A commercial plane uses 1 gallon of jet fuel a second, even cruise ships don't do that (8 gallons per nm). And he isn't looking to go hundreds of miles per hour, 100% of the time.

You are going to have good days and bad days when it comes to solar power. You can increase your chances by cruising in the Summer at 20 degrees above or below the equator, but there are also days or nights when the wind doesn't blow. And when some people (me) wouldn't be able to afford thousand dollar fuel bills to run a motor boat. You are also going to have days in the harbor when you aren't cruising to recharge the batteries too. Although for the OP, the 400-600W solar panels on a monohull won't be enough. It would be to run electronics on board, and motor out of port, but not get you around the world.
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Old 27-10-2012, 13:58   #11
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Re: Circumnavigating using Electric Propulsion.

Seems to me a tri-brid is the way to go. A sail boat with enough diesel storage for three days, reserved for coastal use only. Solar drive to assist the sails the rest of the time and as needed (low wind).
Add a small diesel generator that will drive via electric props and sized to re-charge the batteries a bit too (at max efficiency) so normally runs at best speed but only when needed for motoring and surplus goes to charging up to near full charge when the genny is turned off.
Electric drive best sized to 2/3rds hull speed on full power, efficiency is important. Normally at half power giving max battery range.
The option to recharge under sail is now viable but I suspect it's expensive (no idea). I'd rather lift the props and get clean sailing, using solar for recharge. Many want power for A/C, fridge/freezer/hot and cold powered water. That's a lot of batteries.
The GreenPower cats are quite impressive and very expensive. Cost of ownership might be a lot more equal though. I'd be looking at upgrading a cheap 2nd hand boat though, not a big shiny one.
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Old 27-10-2012, 14:24   #12
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Re: Circumnavigating using Electric Propulsion.

Eleven,

Look at the numbers again. Solar cannot reasonably power the propulsion on a boat. Diesel is the only reasonable option for now. Battery power if you have a dock side hookup might be ok for an hour or so of run time, but that's it. Any further any you have to use something else.


Sun devil,

Try the numbers again, with a 2.5kw solar array it will take roughly a day of solar power generation for every hour of run time. And your 5kw motor would equate to about 7hp. How will you mount an array that large on a boat small enough to rely on a 7hp motor?

The array alone will be roughly 250 square feet.
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Old 27-10-2012, 14:34   #13
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Re: Circumnavigating using Electric Propulsion.

I beg to differ. I think the only viable way to have an 'electric' propulsion is by taking a genset along (to produce the electricity).

Batteries are way to inefficient/heavy to store energy for any long term motoring and solar/wind systems are way to inefficient to deliver necessary enery on the go.

So, I think for anybody with a daysailer tied to a marina/grid an electric motor can be a great choice (but not necessarily the least expensive one). It may be an option too for an 'engineless' sailor too perhaps.

Off the grid, and when an engine is really required, we are likely to be stuck with diesels for another moment. So I think.

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Old 27-10-2012, 14:42   #14
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Re: Circumnavigating using Electric Propulsion.

One of the pluses of electric drive is easy use, forward/reverse. ie mooring and close quarters manoeuvring. Using two elec outbards makes life even better. Adding solar means no engine start-up until clear of the marina/river mouth. By then it's genny OR sail.
For long distances daily solar helps sailing with extra power in short calms and ship power normally. A genny provides for coastal and arrival motoring against tide/current without having to worry about battery status. Bigger batteries, smaller engine and tankage.
Genny location, fairly near the stern/battery/drive legs. Diesel drive has to be on and in-line with the prop shafts.
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Old 27-10-2012, 14:49   #15
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Re: Circumnavigating using Electric Propulsion.

Quote:
Originally Posted by SunDevil View Post
He is asking about a boat, not a plane. A commercial plane uses 1 gallon of jet fuel a second, even cruise ships don't do that (8 gallons per nm). And he isn't looking to go hundreds of miles per hour, 100% of the time.

You are going to have good days and bad days when it comes to solar power. You can increase your chances by cruising in the Summer at 20 degrees above or below the equator, but there are also days or nights when the wind doesn't blow. And when some people (me) wouldn't be able to afford thousand dollar fuel bills to run a motor boat. You are also going to have days in the harbor when you aren't cruising to recharge the batteries too. Although for the OP, the 400-600W solar panels on a monohull won't be enough. It would be to run electronics on board, and motor out of port, but not get you around the world.
I realize that. I am talking about the technology itself, making sure people understand why it is not up to snuff with petroleum, because for boats power to weight ratios matter as well, although obviously not as much as it matters for aviation.
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