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Old 26-06-2011, 19:44   #16
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Re: Hybrid electric conversion for a cat

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Originally Posted by Sand crab View Post
1. Why do locomotives use diesel electric motors?
2. Why do these electric yacht motors have such wimpy horsepower ratings like 10 HP. Is it because they have alot of torque as compensation or are they just wimpy motors?
1) Not just locomotives but, an awful lot of ferry boats use diesel electric too! Also the QE2 which also uses electric motors for propulsion. You have much finer control with an electric motor. Kind of important when docking and moving about.

2) The reason why my 9 HP Lynch electric motor can replace my 27 HP Westerbeke diesel is because there is no longer a couple of hundred moving parts like crankshafts, valves, fly wheel, pullies, pumps and alternator that need to be turned. Lot's of pumps trying to push various fluids and oils inside the diesel eats up a lot of energy which never makes it to the prop shaft.
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Old 27-06-2011, 08:23   #17
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Re: Hybrid electric conversion for a cat

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This topic came up a while back. As I said previously the laws of physics dictate that there is no such thing as a free lunch. In other words using fuel to create energy to produce electricity to propel the boat is less efficient than just using the fuel to create energy to propel the boat. The energy loss is almost always as heat. Please note that most of those hybrid Lagoon 420s have now been converted to standard propulsion at a huge expense. Given these facts I have 2 questions.
1. Why do locomotives use diesel electric motors?
2. Why do these electric yacht motors have such wimpy horsepower ratings like 10 HP. Is it because they have alot of torque as compensation or are they just wimpy motors?
1) Locomotives use diesel-electric because of the difficulty building a multi-gear transmission that will reliably handle the very high power locomotives need (1500-9000hp) in a size that can be fitted on the locomotive. A diesel electric can actually deliver significant torque at zero speed (very nice though not absolutely necessary for starting) which mechanical transmissions can't.

2) No transmission losses and no losses on the motor for support equip like alternator, water pump or oil pump, and a lot fewer moving parts so a much larger fraction of the motors output is delivered to the shaft so a smaller motor is needed to get the same power at the prop.
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Old 27-06-2011, 11:55   #18
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Re: Hybrid electric conversion for a cat

9hp is one-third of 27hp no matter what kind of delusions one is under. The performance in adverse conditions will be readily apparent.
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Old 27-06-2011, 13:46   #19
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Re: Hybrid electric conversion for a cat

1 - As indicated by others, diesel electric avoids the need for a slipping clutch when starting. Clutches are hard to build for 1000s of horsepower. The ocean provides a perfect clutch for a propeller so no clutch is needed. For the QE2 et all, multiple generators run an engine. Diesel electric also avoids huge shafts running through the ship.

2 - a 10hp electric motor is about 8kw with perfect efficiency. In practice it is more watts. So one of these motors is about the full capacity of a medium genset. Two motors is about the capacity of the largest genset you are likely to put in a boat.

An interesting piece of locomotive trivia (which I imagine many know but I didn't - I also hope it's true as I like trivia like this).

A long train will always back up before starting to compress the cars together. This is because the locomotive wheels would slip if it tried to start the whole string of cars. Backing up compresses each coupler a few inches (couplers have this play built in). When the locomotive starts forward, it is then only pulling the first car. After going two inches the play is out of the first coupler and the 2nd car starts. After 2 more inches the 3rd car starts.

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Old 27-06-2011, 15:03   #20
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Re: Hybrid electric conversion for a cat

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9hp is one-third of 27hp no matter what kind of delusions one is under. The performance in adverse conditions will be readily apparent.
Mostly it's a matter of how the motor is rated, I have some 2.5 HP GE motors Trak, they are rated for 2.5HP continous, but are rated for 15HP for 1 minute and 10HP for 10 minutes, 5HP for one hour.
So that 9HP motor will most likely run at 20HP for an hour if the batteries will carry it.
Just think about having a bridge not open and there is a 8K current and you need to stop, that 9HP motor could run up to 50HP for a minute or two, then of course you would need to back off.
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Old 27-06-2011, 17:01   #21
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Re: Hybrid electric conversion for a cat

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9hp is one-third of 27hp no matter what kind of delusions one is under. The performance in adverse conditions will be readily apparent.
Hmmm... so mbianka's apparently successful experience with his electrified sailboat constitutes a "delusion"? What first-hand experience have you had with a sailboat equipped with electric propulsion?
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Old 27-06-2011, 21:08   #22
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Hmmm... so mbianka's apparently successful experience with his electrified sailboat constitutes a "delusion"? What first-hand experience have you had with a sailboat equipped with electric propulsion?
The delusion I refer to is that which claims that a small electric motor somehow will do the same work as the typical marine diesel. 9hp is never 27hp.

I sail with a friend here who has a nice electric drive in his heavy monohull. He is not deluded about the power available vs a diesel. It's good for anchorage maneuvers and not much else.
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Old 27-06-2011, 21:42   #23
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Re: Hybrid electric conversion for a cat

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9hp is one-third of 27hp no matter what kind of delusions one is under. The performance in adverse conditions will be readily apparent.
Electric engines produce constant torque, and a diesel never produces it's rated power until at full throttle (and maybe not even then depending on the setup). So, they aren't directly comparable.

That's why a (1 speed) Tesla is so quick.....
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Old 27-06-2011, 22:01   #24
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Electric engines produce constant torque, and a diesel never produces it's rated power until at full throttle (and maybe not even then depending on the setup). So, they aren't directly comparable.
Horsepower ratings are indeed directly comparable. That is what they are used for. Of course a diesel doesn't produce it's rated power until the speed and fuel are at the rated conditions. Electric motors do not have constant torque. They have max torque at stall and that decreases steadily to zero torque at some maximum rpm.
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Old 28-06-2011, 19:21   #25
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Re: Hybrid electric conversion for a cat

If I was to replace the 3GM30F in Juniper I would think about something like a FB1-4001 motor,
At 72 Volts
Continuous rating: 12.8 kw (17.0 hp)
At 144 Volts
Peak output: 75.0 kw (100.0 hp)
Set up with 12 12volt batteries, slow at 18 volts, normal cruising at 36 volts, fast at 72 volts, and turbo at 144 volts,
So is this motor a 17 hp or a 100 hp? or at 18volts maybe 5 hp? what # do you use?
My Yanmar is rated at 27 peak at 3400rpm but I can't get 3600, I can run at 2900 and by the curve I've seen thats about 18-20 hp.
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Old 28-06-2011, 20:37   #26
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Re: Hybrid electric conversion for a cat

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The delusion I refer to is that which claims that a small electric motor somehow will do the same work as the typical marine diesel. 9hp is never 27hp.
Upon further rereading of his post, it appears that although mbianka might not be delusional, he does seem to have a typo in this sentence:

"The reason why my 9 HP Lynch electric motor can replace my 27 HP Westerbeke diesel is...".

Elsewhere he reports having installed a Thoosa 9000 system, which is rated at 9 KW, not 9 HP. So his motor is really around 12 HP, not 9 HP.

Better?

BTW, the Thoosa 9000 is recommended by the manufacturer as a replacement for diesel engines up to 28 HP, so his old 27 HP Westerbeke would fall within that range.

Quote:
Originally Posted by daddle View Post
I sail with a friend here who has a nice electric drive in his heavy monohull. He is not deluded about the power available vs a diesel. It's good for anchorage maneuvers and not much else.
That would be a legitimate data point if we had more details. Any chance you could post his boat size, motor size and propulsion battery pack size?
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Old 28-06-2011, 23:31   #27
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There is nothing correct in item (2) of mbianka's post. That's my issue with it.

I would think only the continuous hp rating is meaningful in a marine application.

A 12hp electric motor replacing a 27hp diesel will be drawing 9kw most of the time in practical usage. One will need a huge battery bank to travel far...and after that a 9kw generator driven by something like a 20hp diesel. Ugh.

I don't know what my friend has here. I'll ask.
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Old 29-06-2011, 06:31   #28
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Re: Hybrid electric conversion for a cat

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1 -
An interesting piece of locomotive trivia (which I imagine many know but I didn't - I also hope it's true as I like trivia like this).

A long train will always back up before starting to compress the cars together. This is because the locomotive wheels would slip if it tried to start the whole string of cars. Backing up compresses each coupler a few inches (couplers have this play built in). When the locomotive starts forward, it is then only pulling the first car. After going two inches the play is out of the first coupler and the 2nd car starts. After 2 more inches the 3rd car starts.
Carl
Carl:

Interesting. I always thought the engineer was not paying attention when the train started moving backwards at the station. But, it makes a lot of sense now. Thanks!
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Old 29-06-2011, 06:41   #29
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Re: Hybrid electric conversion for a cat

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Hmmm... so mbianka's apparently successful experience with his electrified sailboat constitutes a "delusion"? What first-hand experience have you had with a sailboat equipped with electric propulsion?
Adamante:

I think he's just being mean and trying to make me cry as I silently motor past the fuel dock. But after three years with EP that will never happen. He is right I did make a mistake my 9kw motor is 12 HP.
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Old 29-06-2011, 07:08   #30
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Re: Hybrid electric conversion for a cat

I don't think electric is the way to. Otherwise every manufacturer would be installing them. It is occassionally read where Lagoon people are switching back to deisel.

Some of the quickest cars, and motorcycles on this planet are electric, but they have their limits. You have to pull over somewhere, and plug in......i2f
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