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Old 21-08-2010, 11:23   #1
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Electric vs Diesel

Diesle stinks and it's loud but is it a better secondary drive option for my boat?
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Old 21-08-2010, 11:30   #2
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Maybe not - you can get a very long extension cord for the price of a diesel.
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Old 21-08-2010, 11:39   #3
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That's what I have been looking at. The electrics look like the money saver and save on weight plus you can recharge when under sail props/solar/wind turbine. So why isn't everybody pulling out there diesel and going electric?
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Old 21-08-2010, 12:28   #4
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Because when you size out everything you need for a 50 horsepower electrical motor you'll spend more than the diesel. At least that's how it was the last time my friend and I did it. He pulled his old Perkins out of his ketch two weeks ago and studied the options long and hard.

I'm not fan of aux engines in general, but I burn 1 gallon an hour at around 4 knots, and have 150 gallons of tankage plus what I can carry in cans. Forgetting about the cans, that's days worth of motoring. Brand new installed and done you're somewhere in the $15K range for a diesel like that. Try to get anywhere near that with electric.

Edit: I wish electrical was a real alternative and for some people it is. Especially if you just want something for very light maneuvering work. But you will not be able to cross the Panama Canal with an electric unless you have an insane battery bank that you haul behind you on a barge.
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Old 21-08-2010, 12:34   #5
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Gallon for gallon, pound for pound, Diesel delivers more bang for your buck.
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Old 21-08-2010, 12:43   #6
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There is another option. A small reactor-to boil the water-to turn the turbine-to power the alternator-to drive the electric motor. Pre-heat the water with a solar panel-and pump it to the reactor boiler with a wind powered pump. Where is the wind coming from, you ask. From the forward motion provided by the electric motor, of course.
Encase it all in a 4" thick ferro cement boat hull, rigged as a topsail schooner.
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Old 21-08-2010, 14:23   #7
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Try electric drives; the are there...

I recommend you read up on this topic: Green.

I was lucky enough to be invited to see and crew on Green eMotion just yesterday and was pleased by the lack of noise and diesel fumes. She sailed pretty quick too. Beating to windward (amazingly you can squeeze her to sail up to 30 degrees apparent) at 50 degrees she easily sailed at around 8 knots in less than 15 knots wind (props were up).

On the way back Gideon steered her right through the masses of boats at Sail Amsterdam on the electric drives; throttle response was instant and like magic without the usual shaking and noise. We also enjoyed showing off in the locks when we raised the props to clear lots of water plants tangled around the props; beats snorkeling any time.

What a day...


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Old 22-08-2010, 19:41   #8
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This has been covered in the past in the engine forum. To sum it up, electric is only an option if you plan on daysailing and never straying far from your electric hookup. It is the same problem as with electric cars, range. I have built 3 electric cars and they make great commuter vehicles but none of them would work for a multi state drive.

The reason this is a problem is energy density of your power storage. Diesel fuel is incredibly energy dense and it can be moved quite quickly through a hose. Batteries have poor energy density and cannot be charged very quickly. To figure out how much battery capacity you would need is actually quite easy. For most boats, a reasonable approximation of the power draw would be to divide the horsepower of the diesel engine by 2. Then convert that to kilowatts and multiply it by the maximum number of hours you would ever want to be able to motor for. Remember that this is the maximum number of hours between shore power hook ups not just the maximum amount at any one time. This gives you the number of Kw Hrs that you need to store in your battery bank. If the number of batteries this requires hasn't scared you yet, you need to start taking into account things like reduced capacity due to age/temp, reserve capacity etc. I ran a rough calculation for a 35' boat a year or so ago and came up with 18 Trojan T105s. I can't remember how long it could power the boat for off the top of my head but it wasn't exceptional.

There is a common misconception that you can greatly increase your range by adding a solar panel, wind generator, or gas generator. It comes back to simple energy conservation, if you don't put as much energy into the system as you take out, you will be depleting your batteries. These things will increase your range but not by much. Considering that a 30' boat motoring at a conservative speed is consuming 5kw of power, that would be a large generator to keep up and doing it with solar panels or a wind generator is out of the question even in ideal weather conditions.

This brings you back to needing to store all of the energy that you will need. Since it is hard to change the power consumption, the only way to change the number of batteries you need is to use it for less time. For this reason, it only really makes sense for daysailors that are kept at docks with shore power or cruising boats without a schedule to keep that avoid bad weather.

There are many other design considerations if you actually want to go ahead with an electric drive system like voltage, gearing, ac vs dc, etc that I would be happy to talk about. At this point in time, it makes much more sense for the vast majority of people to use an inboard diesel.
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Old 22-08-2010, 21:07   #9
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I'm in my third season using electric propulsion in my 30 foot 8 ton sailboat.
THE BIANKA LOG BLOG: Going electric: Part 1: The why and how
I'll tell you I ain't never going back to having a diesel on board. I cruise the same way and places I did before. I have also gotten use to the smell of clean under the cockpit where the engine use to live. No filters, oil, belts or antifreeze on board.
Got solar, a Marine AirX 48 volt generator and a Honda 2000 and I will travel. My boat lives on a mooring and I mostly anchor when cruising. This has not been a problem. In three seasons my maintenace expense has been $5.00 for an oil change on the Honda. It was a gamble to make the switch once my one time reliable Westerbeke 27 died with 1800 hours on it. But, my conversion was cheaper than a diesel replacement and it was a "turn key" system. I won't say I can do 5 knots forever. But, three knots without drawing down the battery bank is my norm. Plus I can electro sail (adjusting the prop speed to negate it's drag) and it's quiet when I do because there is no iron pig ICE turning down below. I also love it it when the boat makes it's own fuel at anchor.

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Old 22-08-2010, 21:28   #10
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Hmmm...

We've been electric drive for going on six years now and we are still happy campers even though we anchor out 365 days a year down here in the Caribbean...

Then again if there is wind we never bother with the motor.
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Old 22-08-2010, 22:00   #11
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Hmmm...

We've been electric drive for going on six years now and we are still happy campers even though we anchor out 365 days a year down here in the Caribbean...

Then again if there is wind we never bother with the motor.
No one said it wasn't possible, but you're not going to cross the Panama or Suez Canals, or get through the European canals armed with an electric. The Pardey's have no engine of any type and do more sailing than I do (with a Yanmar) so it's obviously do-able, but the guy asked why more people don't do it and yeah, there ya go.
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Old 22-08-2010, 22:23   #12
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There is another option. A small reactor-to boil the water-to turn the turbine-to power the alternator-to drive the electric motor. Pre-heat the water with a solar panel-and pump it to the reactor boiler with a wind powered pump. Where is the wind coming from, you ask. From the forward motion provided by the electric motor, of course.
Encase it all in a 4" thick ferro cement boat hull, rigged as a topsail schooner.

Is this a theory or have you seen it work? And what if it's cloudy out? maybe I'll need to build a bigger boat than I thought and just go nuclear

I guess if you can't use the wind the best answer is break out the oars!

Seriously though. I hadn't thought about the canals. Thank you for that point! I would have been some pissed off with myself after I finished tootling around the capes to find out I had to unexpectedly do it again if I wanted to see the Bahamas! Makes me think about the masts I'll need when I build too. I'll need a way to take them down too won't I?
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Old 22-08-2010, 23:10   #13
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Has anyone looked at a diesel-electric system? I don't think running engines from batteries is realistic, but using a genset to power multiple electric drives seems completely workable. This setup has been used by ocean liners and trains for decades.

The current setup on our boat seems absurd to me: Two auxiliary diesel engines + diesel genset. If I was re-powering I'd set up a large genset hooked to two electric motors for propulsion. And perhaps have a very small genset for running house loads when on the hook. Simple and easy to service.

The advantages I can see would be to reduce the number of engines from 3 to 1 genset (or maybe 2); you could put the genset wherever it makes sense weightwise; and you could fit the electric drives on legs which could be retracted whilst sailing.
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Old 23-08-2010, 02:05   #14
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Snip.. Makes me think about the masts I'll need when I build too. I'll need a way to take them down too won't I?
I'm not sure if this question is the same as the earlier part of your post but just in case.

Traveling the European canals you will definitely need to remove your mast as well as think about how much the vessel draws. I think the depth limitation is around 1.4 meters but you'd need to check that carefully.

The big canals, Suez and Panama, no height restrictions that are going to effect anything you build. Well, not unless you plan something taller than most freighters

P.
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Old 23-08-2010, 02:20   #15
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A serious question here If converting diesel into power via an engine is x percent efficient, then some of that available power is lost in the drive train due to friction etcetera, how can you not have a further loss when you turn that power into electricity and then apply the electricity to turn your drive chain?
I can clearly see the benefits of having a silent electric engine charged at the dock or via solar/wind systems but diesel electric doesn't make sense to me.

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