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Old 17-03-2016, 13:16   #46
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Re: Electric motor for sail boat

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Originally Posted by a64pilot View Post
They actually do much better than a conventional car, my Prius will actually get 60 MPG at 60 MPH, lightly loaded and level ground, seal level, steady state.
Logically you would think due to all the increased weight of the batteries and electric motors, controllers etc. that are not being used, it would do worse than a car not carrying all that excess weight, at least that is what I used to think.
There are a couple of reason it gets such good mileage, one reason is they are not Otto cycle engines at all, they are Atkinson cycle engines, which I had never heard of, but is very old technology.
https://en.wikipedia.org/wiki/Atkinson_cycle
which would not work at all if you didn't have the torque of an electric motor to get you moving, and secondly because you have two big powerful electric motors to accelerate you and pull hills, then you can put in a wimpy internal combustion motor as all it has to do is generate enough power to maintain speed.
Thanks for the Prius info.. I think the difference maybe it is charging when slowing down. I don't think it is applicable to a boat or my wife's driving?
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Old 17-03-2016, 13:43   #47
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Re: Electric motor for sail boat

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Originally Posted by fungod View Post
We went with the 10.0 engine for our 30' sailboat. We displace 8500lbs and the motor produces about 20 horse. It's a 48v system that produces 200amp hours. Our top speed is about 5.5 knots at 2400 rpm. We cruise at about 4.5 knots to conserve just in case. Our range is 10-12 miles.

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10kw is not 20hp. It simply isn't. 10kw is about 13.4hp. No more no less. But these are rated at input (what the motor draws) not at the shaft (where outboards are rated). But luckily electric motors are very efficient, so assuming 95% efficency the maximum shaft Hp would be 12.73hp.


This may be a reasonable trade off, and I can easily see it as such, but it is a tradeoff.
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Old 17-03-2016, 16:30   #48
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Re: Electric motor for sail boat

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Originally Posted by Stumble View Post
10kw is not 20hp. It simply isn't. 10kw is about 13.4hp. No more no less. But these are rated at input (what the motor draws) not at the shaft (where outboards are rated). But luckily electric motors are very efficient, so assuming 95% efficency the maximum shaft Hp would be 12.73hp.
That was what I calculated too.
Which possibly explains his max speed of 5.5 knots for a 30ft boat.
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Old 17-03-2016, 17:14   #49
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Electric motor for sail boat

The point of the Prius comment is to show that things don't always work like you would think. There are many other things possibly that add up to the whole. Prius for example has essentially a constantly variable transmission, computer controls throttle opening and to minimize friction and pumping losses, it operates steady state at or near full throttle with the RPM drug down to match HP output to power required, common RPM is about 1400 at 60 MPH. Oh and read up on the Atkinson cycle engine, it is a marvel of simple efficiency, but is so weak in torque output wouldn't work in an ordinary car, but when coupled with electric motors, it become viable.
I tied into the bus with a scangauge to monitor some things the car normally doesn't display like RPM, throttle opening, spark advance etc., as with anything there are a few nuts that will carry this to the extreme, and the thing is actually a little fascinating.
If your curious go to www.priuschat.com and read for hours, there are many things about the silly thing that optimizes efficiency, for example if your running 30 MPH and that requires x amount of energy, but engine will develop 2x more efficiently, then the engine is run to develop 2x with the excess going into the battery, battery hits full charge, engine shuts down until battery is discharged a little, engine restarted and cycle continues as you just drive down the road, of course as soon as you lift throttle fuel consumption ceases, everything is electric, brakes, AC, engine water pump, everything so you don't even know when the engine is off without monitoring crankshaft RPM and oxygen sensor status.
My best over a long time for actual measured fuel mileage was 72.3 , but that was gaming the thing, driving like Grandma in the country with sole goal to see just how high a sustainable MPG I could squeeze out of it, you get 50 MPG just driving it like an ordinary car, but once you learn the operating principles and work to optimize those, you get 60+ without a loss in average speed.

It possible for example for an electric motor to run at very low RPM and spin a very big prop for efficiency, and do so without transmission losses, since it can be run as a direct drive, you can't necessarily compare an electric motor directly to an internal combustion motor, HP to HP etc. plus if your willing to have full speed be well less than hull speed, then electric drive becomes more practicable for a non cruising boat, and face it, majority of sailboats are not cruised, and spend long time frames with the engine not being run, for the average non cruising sailboat, electric drive may be more practical than we think. Just as a pure electric car like the Leaf, if it is never intended to drive more than 200 miles in any 24 hour period, maybe practicable.

All I'm saying is don't discount this stuff, there may be more to it than we think, I was a complete sceptic on Hybrid cars, but have put 170,000 miles on one in five years, and am now a believer. I think I could live with a cruising boat that could make 5 kts running off of generator alone, knowing I had a battery bank that along with the generator could drive me at hull speed for a couple of hours, and this bank was large enough that I could have a pure electric boat, run AC if I wanted to etc.
May take a Life-PO bank that has a stupid high charge acceptance rate when compared to LA to make it work, but it may be coming, one day?


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Old 17-03-2016, 18:36   #50
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Re: Electric motor for sail boat

Excellent, a64:

One characteristic of the Prius and other
hybrids is that the bearings of the gas
engine only have to work in forward.
A typical gas engine must work their
bearings forward and backward, with
concomitant efficiency losses. The Prius
bearings can have much finer tolerances
and keep those tolerances throughout the
life of the car.

I own 2 Priuses (Prii?) each has over
250,000 miles with no major engine work
nor any brake work. The regenerative
braking works great.

Never had to smog them until this
year when some smog shop
lobbyists got to the legislature and made
us now smog them. What a joke.
I asked the smog shop guy whether he
had seen any Prius fail smog. He said,
"Not even close."
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Old 17-03-2016, 18:52   #51
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Re: Electric motor for sail boat

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Originally Posted by fungod View Post
We went with the 10.0 engine for our 30' sailboat. We displace 8500lbs and the motor produces about 20 horse. It's a 48v system that produces 200amp hours. Our top speed is about 5.5 knots at 2400 rpm. We cruise at about 4.5 knots to conserve just in case. Our range is 10-12 miles.

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Thats interesting. My boat is 30' 8500lbs with a 15 hp yanmar. cruise at 6.5 knots at around 2200 rpm , burns around .7-.8 gallons. I just don't remember what prop, three blade but that's all I remember. Your works for you and mine works for me. Despite the range difference,25 gals diesel, your's sounds very efficient.
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Old 17-03-2016, 19:22   #52
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Re: Electric motor for sail boat

A64,

I would point out again that by law outboards must be rated as the HP developed at the prop, not before the transmission. So when comparing a gas outboard to an electric prop-prop comparison really are a direct comparison.

In this case We are comparing a 9.5kw output electric motor to a 15kw output gas motor. It simply isn't the case that the 9.5kw motor is more powerful, and no fancy prop size difference will change that.

Want to sing a larger prop on the electric, fine, I'll get a larger prop and slower transmission on the gas motor. it doesn't change the fundamentals of what kW and hp mean.
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Old 17-03-2016, 21:07   #53
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Re: Electric motor for sail boat

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Originally Posted by uncle stinkybob View Post
Thats interesting. My boat is 30' 8500lbs with a 15 hp yanmar. cruise at 6.5 knots at around 2200 rpm , burns around .7-.8 gallons. I just don't remember what prop, three blade but that's all I remember. Your works for you and mine works for me. Despite the range difference,25 gals diesel, your's sounds very efficient.
And that's the crux of it.

If all you need is a 10-12 mile range at 4.5 knots followed by a long period hooked up to shoredpower, then electric is the way to go.

If you want up to a couple of hundred mile range at 6.5knots and rapid refuelling, then 25 gals of diesel is the way to go.
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Old 17-03-2016, 21:14   #54
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Re: Electric motor for sail boat

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Originally Posted by Stumble View Post
A64,

I would point out again that by law outboards must be rated as the HP developed at the prop, not before the transmission. So when comparing a gas outboard to an electric prop-prop comparison really are a direct comparison.
It would be nice if they followed the law. From the link posted earlier:
Motor type: PMAC* Brushless
Voltage: 48 volts
Current: 200 amps
Max power input: 10.0 kW


48V x 200A = 9.6kW

It's physically impossible to generate 10kW at the prop with 9.6kW power consumption at the motor.
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Old 17-03-2016, 21:25   #55
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Re: Electric motor for sail boat

Doesn't that say max power input is 10k, not output?

Sounds like they are feeding it 96% of the allowable max. This seems reasonable. Useable output power would be 9.6kw - heat and friction losses = something < 9.6kw.

But it is a nominal 10kw motor.


A twenty horse gas outboard isn't 20hp at a quarter throttle. But it's a nominal 20hp engine.

My Yanmar is 27hp one hour rating and 24hp continuous rating. That's at the tailshaft DIN rating. Propshaft and cutlass bearing losses not included. But it's a nominal 27hp engine.

A 9.9 outboard is rated as such because of some legal issues. Is it really a 9.9hp engine.
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Old 17-03-2016, 23:32   #56
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Re: Electric motor for sail boat

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Doesn't that say max power input is 10k, not output?

Sounds like they are feeding it 96% of the allowable max. This seems reasonable. Useable output power would be 9.6kw - heat and friction losses = something < 9.6kw.

But it is a nominal 10kw motor.


A twenty horse gas outboard isn't 20hp at a quarter throttle. But it's a nominal 20hp engine.

My Yanmar is 27hp one hour rating and 24hp continuous rating. That's at the tailshaft DIN rating. Propshaft and cutlass bearing losses not included. But it's a nominal 27hp engine.

A 9.9 outboard is rated as such because of some legal issues. Is it really a 9.9hp engine.
Doh! I completely missed that the word was "input".

That's some marketing ploy. Who cares about the "Max Power Input" of a motor. All the end user is interested in is the output power
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Old 17-03-2016, 23:51   #57
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Re: Electric motor for sail boat

Good, I was hoping that simple error had occured.

They call it a 10kw motor because that is what it says on the box it came out of. lol. Probably don't have a clue what the output is. Makes me want to look at a one horse bench grinder and see what the volt/amps rating is on the label.


If they wanted to truly compare these disparate engine types a brake horse power test would tell the tale.

Run each engine or motor at max power, then measure the force required to stop rotation. Simple.

Maybe put a straingauge on a length of three strand and toss it in the spinning prop. :-).

And make a YouTube vid of it.
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Old 18-03-2016, 01:19   #58
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Re: Electric motor for sail boat

Quote:
Originally Posted by StuM View Post
It would be nice if they followed the law. From the link posted earlier:
Motor type: PMAC* Brushless
Voltage: 48 volts
Current: 200 amps
Max power input: 10.0 kW


48V x 200A = 9.6kW

It's physically impossible to generate 10kW at the prop with 9.6kW power consumption at the motor.
Only gas outboards are regulated like this, electrics can do whatever they want. It's tied to emission standards.


For what it's worth, the reason outboards are rated as 9.9hp is because of the regulatory changes that occur when you have a 10hp or bigger engine.
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Old 18-03-2016, 08:19   #59
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Re: Electric motor for sail boat

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The point of the Prius comment is to show that things don't always work like you would think. There are many other things possibly that add up to the whole. Prius for example has essentially a constantly variable transmission, computer controls throttle opening and to minimize friction and pumping losses, it operates steady state at or near full throttle with the RPM drug down to match HP output to power required, common RPM is about 1400 at 60 MPH. Oh and read up on the Atkinson cycle engine, it is a marvel of simple efficiency, but is so weak in torque output wouldn't work in an ordinary car, but when coupled with electric motors, it become viable.
I tied into the bus with a scangauge to monitor some things the car normally doesn't display like RPM, throttle opening, spark advance etc., as with anything there are a few nuts that will carry this to the extreme, and the thing is actually a little fascinating.
If your curious go to www.priuschat.com and read for hours, there are many things about the silly thing that optimizes efficiency, for example if your running 30 MPH and that requires x amount of energy, but engine will develop 2x more efficiently, then the engine is run to develop 2x with the excess going into the battery, battery hits full charge, engine shuts down until battery is discharged a little, engine restarted and cycle continues as you just drive down the road, of course as soon as you lift throttle fuel consumption ceases, everything is electric, brakes, AC, engine water pump, everything so you don't even know when the engine is off without monitoring crankshaft RPM and oxygen sensor status.
My best over a long time for actual measured fuel mileage was 72.3 , but that was gaming the thing, driving like Grandma in the country with sole goal to see just how high a sustainable MPG I could squeeze out of it, you get 50 MPG just driving it like an ordinary car, but once you learn the operating principles and work to optimize those, you get 60+ without a loss in average speed.

It possible for example for an electric motor to run at very low RPM and spin a very big prop for efficiency, and do so without transmission losses, since it can be run as a direct drive, you can't necessarily compare an electric motor directly to an internal combustion motor, HP to HP etc. plus if your willing to have full speed be well less than hull speed, then electric drive becomes more practicable for a non cruising boat, and face it, majority of sailboats are not cruised, and spend long time frames with the engine not being run, for the average non cruising sailboat, electric drive may be more practical than we think. Just as a pure electric car like the Leaf, if it is never intended to drive more than 200 miles in any 24 hour period, maybe practicable.

All I'm saying is don't discount this stuff, there may be more to it than we think, I was a complete sceptic on Hybrid cars, but have put 170,000 miles on one in five years, and am now a believer. I think I could live with a cruising boat that could make 5 kts running off of generator alone, knowing I had a battery bank that along with the generator could drive me at hull speed for a couple of hours, and this bank was large enough that I could have a pure electric boat, run AC if I wanted to etc.
May take a Life-PO bank that has a stupid high charge acceptance rate when compared to LA to make it work, but it may be coming, one day?


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I understand with hybrid cars, they can optimize the IC engine to run at peak efficiency but IC engines in conventional drivetrains are typically running at or close to peak efficiency at highway speeds. At that point it's a balance between conversion losses in the hybrid system (of which there are many variations) vs how closely the conventional drivetrain is optimized to your exact speed. It's in city driving where the IC engine in a conventional drivetrain spends a large part of the time outside peak efficiency that hybrids can provide significant benefits.

On a side note, I think you are missing something with the prius engine. At highway speeds both hybrid and conventional engines need to put out roughly the same HP (ignoring losses and assuming they aren't plug in hybrids pulling significant power from the battery bank). If the prius engine is down at 1400rpm and the engine in a conventional drivetrain typically runs up around 3000rpm, by definition, the prius engine must be putting out more than twice the torque as HP = torque * rpm.

Yes, if you purposely drive like granny to maximize efficiency, you can improve both hybrid and conventional. This is one of the big issues when people claim electric drivetrains in boats need less power. It usually comes with substandard performance and you could make big efficiency improvements with conventional drivetrains by accepting similar limitations.

Example: I typically run at 6.0-6.5kts and figure 6mpg. I've played with dropping back to around 4.5kts and figure it jumps up to 10-12mpg. If I never wanted to exceed 4.5kts, I could drop back to a 10-15hp engine...very similar to the folks claiming you need less HP with electric motors. But in a few situations, I've needed the full 7-7.5kt hull speed for 15-30minutes and the engine provided it without a fuss (other than being noisy at WOT). An underpowered electric motor would have left me scratching my head how to get upriver against a 5kt current.
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Old 18-03-2016, 09:56   #60
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Re: Electric motor for sail boat

One other thing I believe is missing, the automobiles like Tesla and Prius run brushless DC motor with hundreds of volts AC current, must be more efficient as there was Hell to pay to get automobiles with hundreds of volts battery banks through all the requirements, people were of course terrified of being electrocuted, they aren't running brushed DC motors off of low voltage.

Now I said form the beginning I believe that the near term future for electric drive is for a non cruising boat, which I believe is the majority of sailboats, an electric drive ought to appeal to the masses, cruisers are I believe a minority of boat owners, and I believe are less likely to buy a new boat than the average buyer, but I have no data to back that up, just observation is all.

But if coupled with a generator that could drive my boat at 70% of hull speed, I could live with an electric drive for cruising, especially if it brought such advantages as a pure electric boat could have, one with a large enough battery bank that I could run the AC overnight for example, yes all I'd be doing would be to shift the generator run time to the next morning, but heck it would be nice.
I know there would be times I'd need full power, maybe for a couple of hours, and at that time both the generator and the battery bank would be called on to give me that full power. Back to that Prius, it is only a 75 hp motor, yet will accelerate to 60 MPH in 9 sec, because it has about 50 HP of electric motors to add to it, boat could do the same.

All I'm saying is it's feasible is all, and may well be the best thing for the average sailor who will never really leave the bay and returns to work on Mon. morning and may one day find itself in cruising boats.
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