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Old 06-09-2009, 00:58   #46
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Originally Posted by s/v Jedi View Post
Also, what is often overlooked is that the conventional diesel drive for a small boat always uses a gearbox, which introduces losses just like the diesel-electric conversion loss. As you do not need a gearbox for diesel-electric, you gain, compensating the conversion loss (in part?).

When you use a diesel genset to charge batteries and use the batteries to power an electric drive, you loose a lot in the battery charge/discharge process. You do not have this loss when you first run down the batteries with the electric drive and next switch over to diesel genset to both drive the electric motors and charge the batteries.

I think the whole concept makes a lot of sense and it gets better with solar and/or wind gen power sources added to the picture. I would give it a lot of thought when the need for re-powering comes up.

And remember that submarines have been doing this for a long time, it's proven technology.

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Non-nuc subs aren't that great. They spend most of their time on the surface charging their batteries. According to the link below the height of development was 26 knots for a short time, or 10 days at 3 knots underwater.

submarine (ship) :: Toward diesel-electric power -- Britannica Online Encyclopedia
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Old 06-09-2009, 01:05   #47
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Trains have also been doing it for years.
For me the biggest advantage would be the elimination of one engine.
With conventional diesel drives you still need a generator if you want some creature comforts that take a lot of juice like AC.
With diesel electric there need not be the second engine.
I did consider it when I repowered…I was looking at Glacier Bay’s 277volt system but according to them it was still a bit early for a boat in my size range.
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Old 06-09-2009, 01:17   #48
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But what if you only use the Genset on a very rare occasion, are only using the motor briefly to get in and out of the slip, and are recharging it with wind and solar? Then you would indeed have a more efficient rig in the long haul, you just have to look at the long term picture.
Exactly my point.

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When you use a diesel genset to charge batteries and use the batteries to power an electric drive, you loose a lot in the battery charge/discharge process. You do not have this loss when you first run down the batteries with the electric drive and next switch over to diesel genset to both drive the electric motors [directly from the generator] and charge the batteries.
Yes, exactly.

As far as I can see, this hybrid system could offer the best (and a viable) solution for sailboats. I'm now wondering about the size (physical + power output) and cost of a suitable generator along with suitable electric motors. Any pointers?
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Old 06-09-2009, 01:37   #49
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Remember that your motoring is not just limited to getting in and out of a slip.
Its a very important piece of safety equipment
I believe that you should have the power stay off a windward shore when the tide, current, seas and wind are on your nose.
What it takes to push a boat along and what it take to save her are two different things.
Of course it does depend on where and how you sail...I guess I generally assume the cruisers scenario.
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Old 06-09-2009, 01:39   #50
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I dont get the energy conversion. your going to turn diesel into mech, mech into electric and electric into propulsion. each time theres a transaction, theres waste. Its the law of physics. What is the advantage here cos i dont see reducing to one engine as a way forward, it just puts more hours on the only system. OK, it might simplyfy the drive train/transmission and cables are easier to route than shafts but i cant help thinking theres a trade off.
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Old 06-09-2009, 02:34   #51
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In my proposal I mentioned that the two hour battery duration would cover entering/leaving moorings and the batteries would be recharged from solar/wind. So most of the time the genset would not be required, thereby increasing real-life overall efficiency.

In terms of power losses there's a transaction from diesel engine to gearbox to propulsion. With an electric motor system no gearbox is needed - the motor turns the propeller directly, which is more efficient. This would partially offset mech > elec > mech inefficiency, which, don't forget, isn't always required anyway (see above).

One of the earlier arguments was that a genset would charge the batteries, which would run the engine. I agree this adds an extra transaction and decreases overall efficiency. However, what I've proposed is using a genset to drive the electric motors directly, thereby reducing the number of transactions and increasing efficiency.

Running one engine to achieve a certain power output is more efficient than running two engines for the same total output (although a cat can happily run on only one of its two engines). Two engines are also 2 x the cost. That was my reasoning for one engine.
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Old 06-09-2009, 02:42   #52
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Remember that your motoring is not just limited to getting in and out of a slip.
Its a very important piece of safety equipment
Agreed (but try telling that to the Pardey's).

Quote:
I believe that you should have the power stay off a windward shore when the tide, current, seas and wind are on your nose.


Agreed. The hybrid system I proposed would do that, in terms of duration. Or are you talking about engine power? Powerful electric motors are available to compete with sailboat auxiliary diesel engines. You only have to look to the electric car market to realise that.
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Old 06-09-2009, 05:39   #53
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Rising Star, could you elaborate and give more details on your power grid on your vessel? Could you give model numbers for the DC appliances and let me know if you are using LED lighting?

Anyone out there using Lifeline AGM batteries? Other gel or AGM that you recommend?
I have one 200W 48V solar panel, switchable to recharge 2 banks of 4 Group 31 AGM batteries. I also have one 50W 12V panel to recharge 2 wet-cell Group 31 house batteries. Refrig. (CoolBlue unit) is powered off the the motor bank utilizing the excess solar power produced.

DC appliances are minimal - VHF, EEE PC as chartplotter, depth & speed, and lights. We have one LED overhead, the rest are standard 10W. The anchor/masthead lights are LED.
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Old 06-09-2009, 08:11   #54
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One advantage to diesel electric that I haven't seen mentioned inj this thread is the flexibility it allows in the installation of your power plant. In my case I see a potential benefit in mounting the electric motor to the prop shaft while allowing installation of a genset in the best location for access/maintennce. My current setup uses a V-Drive and access to some areas is pretty tough.

Another benefit is many modern gensets are really quiet and even running the gen for power it could be a lot less intrusive than running a diesel engine drive.

However, my initial research I don't see systems that have the power to drive a larger boat, especially when, as pointed out by James S, you want enough power to motor off a lee shore or against a strong current.

I looke on Electric Yacht - Electric Yachts: Battery powered sailboat auxiliary motors that are CLEAN . GREEN . QUIET and the largest system they offer has max 18 HP vs the 58 HP diesel currently installed. Like most internal combustion engines this is likely rated at the crankshaft and a significant percentage will be lost in the transmission, driving the alternator, water pumps etc, but I would guess at least 35-40 HP is available at the prop shaft. A couple of other sites that offer electric drive systems seemed to have similar max HP motors.

So, anyone know of a system suitable for larger boats?
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Old 06-09-2009, 09:09   #55
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Originally Posted by skipmac View Post
.
I looke on Electric Yacht - Electric Yachts: Battery powered sailboat auxiliary motors that are CLEAN . GREEN . QUIET and the largest system they offer has max 18 HP vs the 58 HP diesel currently installed. Like most internal combustion engines this is likely rated at the crankshaft and a significant percentage will be lost in the transmission, driving the alternator, water pumps etc, but I would guess at least 35-40 HP is available at the prop shaft. A couple of other sites that offer electric drive systems seemed to have similar max HP motors.

So, anyone know of a system suitable for larger boats?
Skipmac,

Comparing an electric motor to an ICE (internal combustion engine) is comparing apples to oranges.

The ICE drives pumps, alternator, many moving parts and produces large amounts of heat - all a power loss. An electric motor puts a significantly higher percentage of power to the shaft. The 18 hp electic motor you referred to could be equivalent to between a 36 hp to 55 hp ICE engine - depending the engineering experts you believe in. I replaced a 22 hp diesel ICE with a 6 hp electric. How you prop your electric boat is also different from the ICE boat.
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Old 06-09-2009, 11:10   #56
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There's a lot of confusion here. I'll try to clear it up...

First, diesel-electric drive is without batteries. A diesel genset delivers electrical power that is fed to an electric motor that spins the prop (in a boat).

When you introduce batteries, you get a diesel-electric-hybrid setup. Now, you can use the batteries to power the electric motor in addition to the normal diesel-electric drive. When the diesel is running, it can provide both power for driving the motor plus power for charging the batteries.

A good read is, as always, on wikipedia: Diesel-electric transmission - Wikipedia, the free encyclopedia and Traction motor - Wikipedia, the free encyclopedia

Quote:
Non-nuc subs aren't that great. They spend most of their time on the surface charging their batteries. According to the link below the height of development was 26 knots for a short time, or 10 days at 3 knots underwater.
What's not great about that!!?? 10 days continuous powering on battery alone! Or 26 knots speed? That's all impressive. At the surface, they are not just charging their batteries, they use the diesels to generate electric power for both propulsion and charging batteries.
Diesel-electric subs are the hunter-killers, going after the nuclear subs.
Quote:
For me the biggest advantage would be the elimination of one engine.
You can do that, or install two smaller gensets instead of one larger. This is what I would do. You get redundancy and more efficiency because for low power you can run just one, and bring the 2nd generator on-line when full power is needed.
Quote:
I believe that you should have the power stay off a windward shore when the tide, current, seas and wind are on your nose.
You can get as much power as you need. Look at the first photo in the Wikipedia page; the people around that engine/prop look like ants: that is a huge ship!
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I dont get the energy conversion. your going to turn diesel into mech, mech into electric and electric into propulsion. each time theres a transaction, theres waste. Its the law of physics.
With conventional diesel, you have the losses in the gearbox, which essentially is a mech into mech conversion. I think the loss in the gearbox is comparable to the mech into electric conversion. So, the only extra loss is in the electric motor.

I just checked this out. The efficiency of electric-generator and motor is 90%. So, coupled in series, you put 90% * 90% = 81% of the diesel power into the shaft.
I also found that gearbox loss is 10% too. So the extra loss with diesel electric is 9%. For a 75 hp diesel, this is 6.75 hp, about the same as a 200A 12V alternator. When you use two smaller generators instead of one big unit, you will probably win this right back under cruising speed or motor sailing, when you can get by with only one genset running (at high load equals more efficient as compared to a big diesel engine running at low load).

So, I think that in a real world situation, you can get the same range out of your diesel. You only loose if you go flat out all the time.

And this is without solar. When you throw that into the mix, the picture changes again. No way you can use solar for your drive when you have a conventional diesel. When your batteries are full, the solar array can play around a bit while most of it's output is just wasted. With diesel electric drive they can help spin your prop when you go on battery alone, greatly improving your range on battery, plus, when you shut the propulsion down again, they find batteries that are ready for a good charge!

ciao!
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Old 06-09-2009, 11:15   #57
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Agreed (but try telling that to the Pardey's).



Agreed. The hybrid system I proposed would do that, in terms of duration. Or are you talking about engine power? Powerful electric motors are available to compete with sailboat auxiliary diesel engines. You only have to look to the electric car market to realise that.[/FONT][/COLOR]
I did look and I didn’t see any electric car motors that would be a suitable replacement for my 85hp that would be happy tucked away deep in my bilge.

I think there is a bit of difference when we start to look at cooling.

Don’t get me wrong...I was willing to go electric, and very excited at the prospect of it, but I'm a full keel 39,000lb blue water boat...and I think I probably like a few more comforts than the Pardey's.
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Old 06-09-2009, 14:27   #58
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Come on James, you can do better.

My Google search for a 50hp electric traction motor returned 34,900 hits. The first page shows two links that got my attention:

An electric Mini Cooper with 4 motors of 160 hp each, one for each wheel:
Electric Mini: 0-60 in 4 Seconds: It Has Motors In Its Wheels : TreeHugger

City Electric Motor will ship you a 25-25,000hp electric traction motor same day:
City Electric Motor Company Inc.

No, that part is easy.

ciao!
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Old 06-09-2009, 19:40   #59
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Skipmac,

Comparing an electric motor to an ICE (internal combustion engine) is comparing apples to oranges.

The ICE drives pumps, alternator, many moving parts and produces large amounts of heat - all a power loss. An electric motor puts a significantly higher percentage of power to the shaft. The 18 hp electic motor you referred to could be equivalent to between a 36 hp to 55 hp ICE engine - depending the engineering experts you believe in. I replaced a 22 hp diesel ICE with a 6 hp electric. How you prop your electric boat is also different from the ICE boat.
Yes, that was exactly my point. The HP of an ICE at the crankshaft is not the HP delivered to the prop shaft. With an electric motor the HP of the motor is pretty much what you get. But are you telling me that I can replace my 58 HP diesel with an 18 HP electric and get the same speed/power against a strong head wind and seas in a fairly heavy, high windage 42' boat?

Maybe there's an engineer out there that some data on powertrain losses but I would bet that I am getting at least 30-40 HP of my 58 rated HP to the prop. Hard for me to believe that I could get the same performance from an 18 HP electric motor.
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Old 06-09-2009, 20:48   #60
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Reality

It's true after you add your assorted losses, power to prop is still power to prop. Problems have always been what is you best shot at running at optimum performance ? IF you were properly propped to run at hull speed with your engine at optimum rpm then you get to compare flat out run for an electric drive. Nigel Calder has a nice set of articles in proboat bullder mag, I think a year or so ago.

From my own personal experience. almost never run my diesel that fast. So in the wrong power band or not propped for the speed I am running. And still it stinks for marina maneuvers. My suboptimum habits for a normal cruiser probably wastes 30% of what it could deliver. I run the main to charge my batteries, run the seafrost etc. and that too is a major energy bandit.

Better overall savings if you can use a genset as it was designed, to charge batteries at the optimum load and rate, Use an electric motor that delivers constant torque no matter what rpm. You can usually run your electric drives harder than cruising spec for some limited time before motor or controller overheats, gets your thru the channel mouth.

But we will have to sacrifice that extended MAX thrust our larger HP diesel can deliver, but how often do you push that throttle all the way for hours.

AS mentioned above, can charge the batteries via solar, marina or with modest performance loss via regen. THe major problem for all is higher density energy storage in diesel than batteries. Without regen, long runs with the main diesel propulsion at "optimum" speed still gives better efficiency and range than diesel-electric, just not my usual daily use.

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