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Old 22-07-2008, 14:19   #1
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Range using electric propulsion

I started a thread with regards to converting my boat to electrical propulsion. My biggest concern and one which many people highlighted was the short range. I was thinking last night that perhaps this can be alleviated by mounting a bracket and an outboard. this would fill the void while you are charging your batteries during a time when their is either too much or not enough wind to sail. With no wind i can see no likely situation for the outboard not to function properly. But how would an outboard fair in conditions so bad that you aren't able to sail? Also is it worth putting more penetrations in the hull of the boat?? Anybody have any input on this setup and any foreseeable problems?
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Old 22-07-2008, 15:07   #2
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But how would an outboard fair in conditions so bad that you aren't able to sail?
They don't like being totally under water. Salt water especially. Waves and such can tend to make that happen. They also require gasoline. Nasty stuff to store as it is heavier than air and has a propensity to explode. Very unhealthy.

In terms of range the problem is you quickly find that it takes longer to charge the batteries than it does to drain them under almost any situation and no matter how many batteries you have or how you charge them. Battery charging is a complex process and we actually have a lot of discussions about battery charging. It should prove most interesting for you. Check the electrical forum.

Good news - There is never too much wind to sail. It isn't always fun though.
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Old 22-07-2008, 21:46   #3
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Seriously, I think that "hybrid" forms of propulsion will become the norm over the next 25 years in both cars and boats. In a boat, you would charge the batteries using solar or a wind generator while you were under sail.
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Old 24-07-2008, 10:46   #4
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If you are going to use an electric motor for propulsion you need a generator that is large enough to operate it.

So, at anchor you would want to use wind and solar sources of energy to charge the batteries, and use the generator as a backup. When sailing you might also use a towed device. For motoring very short distances you could just suck the battery bank down. If you have to motor for long distances, though, there is no way a battery bank is going to last--it would just have to be WAAAAAY too large! And so you would fire up the generator and power the electric motor from that.

I don't see any other way to do it.
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Old 24-07-2008, 11:01   #5
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You could have a diesel-electric, just like a WW II submarine. You charge the batteries using solar or a wind generator, but the diesel also has a generator. You run on electricity as much as you can, but you have the diesel for emergencies.

I'm not an engineer, but my guess would be that the electric motor won't add much weight. But the batteries will.

Boats need weight in the keel. Maybe you could design a keel that is a giant lithium-ion rechargable battery, like the one in your laptop. That way the extra weight is in the right place.

Juast trying to think out of the box.
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Old 24-07-2008, 12:28   #6
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Hank,

The outboard will serve as a stop-gap solution when you're low on electricity, but it somewhat defeats the purpose of going electric in the first place: now you're back to internal combustion for propulsion (and an OB, unlike the diesel, offers no charging benefit of any consequence to the battery bank while running).

The math is difficult to overcome on this one. Paul put his finger on it above:
Quote:
In terms of range the problem is you quickly find that it takes longer to charge the batteries than it does to drain them under almost any situation and no matter how many batteries you have or how you charge them.
It seems as if you'll have to accept some limitations:
1) You will have to budget distances, energy draw and likely ability to recharge whenever you consider flipping the motor on (what will be the conequences to my all-electric auxilliary propulsion system of motoring X miles to Z location?).
2) There will be times you will be stationary, e.g., after a long motor-sail and dropping the hook, and not be able to motor further until there is sufficient charge in the batteries.
3) If you're relying on passive charging sources, you will be at the mercy of the available sunshine/wind, which will often not offer their bounty of energy when you'd like, leaving you at No. 2 above.

Until the technology improves, this is the real world if you don't want to burn fuel. But in the larger picture, it' only been since the last half of the twentieth Century that 27' (and larger) private yachts such as yours have relied on auxilliary engines. Eric Hiscock cruised the whole western England/Scotland, and Ireland in the Thirties with no engine. I don't recall reading anywhere that he complained. It definitely will improve your seamanship.

Depending on how you intend to use the boat, these limitations may be quite acceptable.

I missed the other thread: what route are you considering on your drawingboard for recharging?

Fair Winds,
Jeff
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Old 24-07-2008, 12:40   #7
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Maybe you could design a keel that is a giant lithium-ion rechargeable battery, like the one in your laptop. That way the extra weight is in the right place.
The weight issue is almost as close as keel ballast. LiIon batteries are not the best choice. They age from the day they are made even if not given use. I believe the last I checked the FastCat power system uses about 1600 lbs of batteries (12 Group 4 AGM's). Electric drives are not what you would call light weight after you include the batteries they require. Our boat has over 5,000 lbs of ballast so you could make the top of the keel into a battery compartment. Currently the battery bank is about 300 lbs. That with the alternator does a fair job running the fridge and the rest of the gear. 2 solar panels only help and can't carry the real load.

Scaling that up to say 1600 lbs leave a charging deficit that really is huge. Electric motors are great for converting watts into thrust. Storing watts from anything on the other hand basically sucks.
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Old 24-07-2008, 12:49   #8
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3) If you're relying on passive charging sources, you will be at the mercy of the available sunshine/wind, which will often not offer their bounty of energy when you'd like, leaving you at No. 2 above.
What about a sail hung from a tall mast? the attempt to avoid the instability of sails and old fashioned solar power brings you full circle from where you began. We really don't have adequate technology to store energy in significant amounts. In terms of the global economy we really have no ability to store any amount of energy save for leaving the oil in the ground and the coal buried and the water dammed up. Even nuclear power is not stored. The ability to create energy and then hold on to it is clearly child like compared to the ability to make it and consume it.
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Old 25-07-2008, 07:24   #9
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regeneration

One thing to keep in mind is the electric drive motors can also be used to generate electricity.

Using a reasonably high-drag 3-blade prop, while sailing you engage the motor to slightly below your average speed which reduces the drag to near zero. But every gust, wave-induced acceleration, etc. will be producing juice. If you've plenty of wind and you're willing to take the hit to speed, reduce the motor speed further and you'll be making electricity all the time you're sailing, turning your motors into a towed generator.

Water is far denser than air, so a towed generator is more efficient than a wind generator, but it is limited by the speed of your boat.
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Old 25-07-2008, 13:43   #10
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Originally Posted by Curmudgeon
Boats need weight in the keel. Maybe you could design a keel that is a giant lithium-ion rechargable battery...
Now THAT'S an idea!
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Old 25-07-2008, 13:49   #11
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Originally Posted by Pblais
We really don't have adequate technology to store energy in significant amounts.
That's the big problem. I was reading an article several years back geared towards those who live in homes off the grid, and who rely on solar, wind, micro-hydro for their power. The article mentioned batteries and their rather pathetic ability to store a significant amount of energy. The author did the math and calculated that if battery capacity had increased during the 1990s at the same rate that computer hard-disk capacity increased during that time, the average American would be able to power their house (including air conditioning and everything else) for an entire year on a battery smaller and lighter than the typical car starter battery.

Gee, wouldn't that be nice?
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Old 25-07-2008, 13:49   #12
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Well, a keel that's a battery is a little futuristic, but why not?

In vehicles, one of the big issues with electric power is the weight of the batteries. (The longevity, capacity and ease of recharge are separate issues.) But a sailboat NEEDS weight-- alot of it. So put the battery in the keel. Seems logical to me.

Yes, improvements in battery technology have lagged. But it will improve out of necessity, as fossil fuels are phased out. You will start to see alot more sailboats and fewer powerboats too.
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Old 25-07-2008, 13:52   #13
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Originally Posted by Pblais View Post
The weight issue is almost as close as keel ballast. LiIon batteries are not the best choice. They age from the day they are made even if not given use. I believe the last I checked the FastCat power system uses about 1600 lbs of batteries (12 Group 4 AGM's). Electric drives are not what you would call light weight after you include the batteries they require. Our boat has over 5,000 lbs of ballast so you could make the top of the keel into a battery compartment. Currently the battery bank is about 300 lbs. That with the alternator does a fair job running the fridge and the rest of the gear. 2 solar panels only help and can't carry the real load.

Scaling that up to say 1600 lbs leave a charging deficit that really is huge. Electric motors are great for converting watts into thrust. Storing watts from anything on the other hand basically sucks.
The weight of the AGM batterys used is actuall 11 x 42 kilo or 462 kilo , 1000 lbs and the same in Lithium Phosphate Ion is 75 % lower or 115 kilo , 265 lbs.
It only gives us 3 hours at 6 to 7 knots before having to start a generator but we do sail so it poses no problem.
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Old 26-07-2008, 23:05   #14
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I don't even want to think about the repair expense after running hard aground with a Li-Ion battery keel...
Ouch!

Steve B.
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Old 27-07-2008, 02:16   #15
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I don't even want to think about the repair expense after running hard aground with a Li-Ion battery keel...
Ouch!

Steve B.
I dont see that as a huge issue. Obviously you would "armor plate" the leading and trailing edeges of the keel. You would also design it as a full keel with a gentle taper on the leading edge. My guess is that corrosion would be a bigger issue.

When you drop your laptop, it's almost never the battery that breaks.
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