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Old 17-11-2016, 14:10   #361
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
BTW, the OceanVolt projections for Conrad Colemans 60' IMOCA Class were 7.2 knots at 7kW, and that is what was achieved in reality. Another data point that the OceanVolt projection algorith is valuable. But that doesn't mean you can go 10 knots using 10 kW, because it is not straight line, we all know that. In fact for the IMOCA 60 to go 7.8 knots would take about 10kW!! so it is out of the sweet spot.

Coleman also got 4.5kW of power, yes that's not a typo or misquote or hype or a lie, it is what it is as logged by accurate calibrated instruments, 4.5 kilowatts of power on the OceanVolt regen across the Atlantic, so no, you do not need a rotating saildrive to get significant regen power.

Now, is there anything to discuss that would be of benefit for cruisers in any of this??
If that data point is actual measurement instead an estimate, perhaps you could be more specific and let us know where is that power measured:
1) mechanical power between ICE and generator (angularspeed * torque)
2) electric power between generator and motor (voltage * current)
3) mechanical power at the prop shaft (angularspeed * torque)
They are definitely not all 7 kW while that imoca has speed of 7.2 knots, and providing those would tell a lot about already existing systems available on the market.
I believe you, that 4,5 kW electrical power is effective amount, but tells us absolutely nothing at all about the low efficiency involved as both speed of the boat and associated drag force are not known while producing that 4.5 kW.
Using a camberless propblades would improve that efficiency some but not as much as rotating the drive leg. On the other hand camberless propblades are significantly less efficient while providing forward thrust for propulsion.
Either way their system seems to have substantial compromises made, that are not difficult to improve. If you can provide more information on the propeller used we would know more.
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Old 17-11-2016, 14:43   #362
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Re: Oceanvolt Hybrid Motor

You are very read on modern tech hey


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So far the extent of Mr. Musk's innovation is a slight change in the standard size of a battery.
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Old 17-11-2016, 14:43   #363
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Re: Oceanvolt Hybrid Motor

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Slightly different topic but something I am confused about that relates to sizing the electric motor. I posted a video showing electric on one cat and diesel on the other in a tug of war. The 10kW electric pulled the diesel boat backwards with 22kW diesels, at wide open throttle on both boats. It wasn't faked and it was done by the charter company not those nasty snakeoil EP vendor.

I don't think there was a good explanation of how this occurs. There were responses that it was garbage video ( whatever that meant), or that tug of wars are completely irrelevant (of course that is true), and so on, but can anyone explain why this happened, especially since it is at WOT.

If it was at lower revs, say 25% power, then the high torque of the electric would out pull the diesel, I think that is agreed. But why does it still happen at WOT when the diesel would be at or near it's maximum torque?

An explanation in laymans terms would be good, without advanced math. On the face of it, it does seem that electric motors for propulsion can be sized at about half the equivalent kW rating and still generate the same, or better, thrust of the diesel.

I realise because they are not moving through the water as fast as they could without being tethered to each other that there is prop slippage & resultant loss of thrust efficiency, but that is true for both of them.

What gives?
There are several independent reasons, but that video does not provide enough information to make any conclusion on which of those reasons were significant in that case and which were not.

First, there is no knowlidge what RPM those diesels were able to have in that test. It is entirely possible RPM never rise above 50% of rpm necessary for full power. Perhaps it was less than 30% meaning available torque was also low compared what that ICE could provide at more revs. As a result those diesels were nowhere near their full power regardless of using WOT.

Second, static thrust of a propeller is not the same for same actual propellershaft power, but depends a lot on propeller dimensions like blade area and diameter and pitch/diam ratio. The latter of those 3 has only significant effect if it is too large leading to blade stalling. It is possible pitch/diam ratio of that diesel powered cat was too large resulting stalling.
Too small blade area could have caused cavitation also severy limiting available static thrust. Diameter has significant effect on propulsive efficiency, meaning how much of power goes to increase kinetic energy of the current produced by the prop, and how much actually goes to boat as a product of thrust force and boat speed.
Static thrust can be in theory made as large as you want in any given shaft power, even 1000 000 N from 10 watts, but it is not practical at all (enormous cost) and assumes no frictional losses in transmission (in bearings or gearbox). In practice bigger diameter leads to more static thrust on any given shaft power, but requires lower revs.

In real world commercially available gearboxes for marine transmission in a given power range don't offer as much torque than those electric motors can easily produce. And that allows those electricmotors to use bigger props with more static thrust with less power used. Measure the thrust while moving forward at speed and the test no longer gives advantage in that respect to electric. That is what you need while going against current and wind in a choppy seas, actual propulsive power, not static thrust. The latter is very useful while docking though helped by superior control of electrical power.
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Old 17-11-2016, 15:02   #364
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Excellent! Thanks Valhalla, and I mean that. Good analysis that is actually helpful.



As I proposed to SVDestiny, it would be "fairer" to have the diesel going first & up to max torque, and see if the electric would then be able to stop it. Right?

No, unless you plan to use your cruising boat as a tug the entire demonstration is useless noise. The only meaningful test comparing two boats would be to do a logged race with a typical cruising itinerary. At the end of the cruise compare all in cost and hours spent on passage with each crew filling out a survey rating their experience. If one boat serves nothing but cold beans and the crew sweats a lot but the other serves good hot meals, baked bread and deserts while living in comfortable temps then the ratings will expose that.

No one is saying EP can't work. It clearly can. But is it better than what is out there now? If not, why do it? So far no one without a vested interest has made a viable case that EP is better in a cruising boat. I hope someone will using real numbers (calculated or empirical).
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Old 17-11-2016, 15:04   #365
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Cotemar View Post
It's all about ENERGY DENSITY.
That too, but not only that.
Cost is even more important, and there is far more potential improvements possible reducing cost than improving energy density. The latter is severely limited by the laws of physics and chemistry, while cost is not, possibly allowing reducing cost to continue as a reality in the future, just like it has been in the past.
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Old 17-11-2016, 15:13   #366
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Re: Oceanvolt Hybrid Motor

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How long would it take a Yanmar 30 to get to max torque? Are you saying it would be 30 seconds?

So overnight I realised a fairer test would be to have the diesel towing the electric at full torque, and then the electric goes to WOT, and then see what happens. If the electric slows the diesel down and eventually stops it, and then the direction of pull reverses, that will be definitive.

Do you agree?
Agree on what precisely?
The result would tell us a lot about which propeller is better at static thrust while not much on which propulsion system in general is better. It would however reveal which propulsion system tested was better at static thrust.

For some diesel+gearbox+prop combinations it's possible the engine never gets rpm needed for max torque under static thrust test, no matter how long you wait for it, yet the same system can be efficient and effective at speed and also be cost efficient to purchase and use and maintain.
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Old 17-11-2016, 15:13   #367
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Re: Oceanvolt Hybrid Motor

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"It's also capable of providing some electric power if necessary, but only very inefficiently.

Are you serious, or were you being ironic? The SD15 in regen mode produces 2Kw at 6.5 knots and Coleman got 4.5kW at higher speeds. That's inefficient???

Not only that, he gets no loss of boatspeed when regenerating! He has commented that his power levels from the OceanVolt SD15 is "brilliant".

The SD15 is his primary source of power. It is to be used for propulsion only in emergency, as is the case with the redundant Fischer Panda 4kW DC genset.
BB, I surely agree that 4.5, or even 2 kw is indeed a useful amount of power.
But, how in the world can one extract that much power with literally "no loss of boat speed"? Perhaps no significant loss, but there must be some loss. IMOCA boats are not much limited by hull speed issues, so any time you add drag (and extracting 4.5 Kw must add drag, for there are no free lunches) the boat speed will be reduced. It may well be a desirable trade-off, but some loss must occur.

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Old 17-11-2016, 20:39   #368
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Jim Cate View Post
BB, I surely agree that 4.5, or even 2 kw is indeed a useful amount of power.
But, how in the world can one extract that much power with literally "no loss of boat speed"? Perhaps no significant loss, but there must be some loss. IMOCA boats are not much limited by hull speed issues, so any time you add drag (and extracting 4.5 Kw must add drag, for there are no free lunches) the boat speed will be reduced. It may well be a desirable trade-off, but some loss must occur.

Jim
Jim,

If there is a loss, it is (apparently) not showing up on either Coleman's instruments onboard either on his test sails across the Atlantic, or this Vendee Globe, according to him. It was a primary issue for him deciding on the OceanVolt.

Remember that it is not a feathering prop that is being locked in reverse gear and being dragged thru the water ( drag of that is obvious) it is a folder that is being kept open by a tiny bit of power drawn from the LFP bank , while the water rushing past spins the prop much faster, thus generating a net surplus of charging power. It surprises, and delights me, to hear of this as I was looking for good regeneration in whatever solution we chose.

I could say more but I won't, as there is some hushhush innovation on the way that will be even more "interesting"
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Old 17-11-2016, 21:01   #369
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
If that data point is actual measurement instead an estimate, perhaps you could be more specific and let us know where is that power measured:
1) mechanical power between ICE and generator (angularspeed * torque)
2) electric power between generator and motor (voltage * current)
3) mechanical power at the prop shaft (angularspeed * torque)
They are definitely not all 7 kW while that imoca has speed of 7.2 knots, and providing those would tell a lot about already existing systems available on the market.
I believe you, that 4,5 kW electrical power is effective amount, but tells us absolutely nothing at all about the low efficiency involved as both speed of the boat and associated drag force are not known while producing that 4.5 kW.
Using a camberless propblades would improve that efficiency some but not as much as rotating the drive leg. On the other hand camberless propblades are significantly less efficient while providing forward thrust for propulsion.
Either way their system seems to have substantial compromises made, that are not difficult to improve. If you can provide more information on the propeller used we would know more.
This (camberless prop blades??) is above my head, I will freely admit. I can say that there is no ICE operating on the boat, at all. The whole purpose of his campaign is to demonstrate that the race can be done using no fossil fuel at all. This boat is not competitive for winning the race as it's a 2005 design which is ancient in IMOCA class, but even so he is leading the slow boats. Everyone ahead of him at this stage is new designs. He is a helluva sailor!

So I believe that it is measured as in your point 2), the kW going into the battery as shown by the OceanVolt controller display.

All the data is being logged in real time by OceanVolt as I've said before, but what the speed to output power values are, I have no idea other than the 2kW at 6.4 knot data point.

If you can deduce that the OceanVolt system has "substantial compromises" that you could easily improve, without knowing the existing engineering, if I were you I'd be sending my CV in to OceanVolt before the race is over.
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Old 17-11-2016, 21:33   #370
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Re: Oceanvolt Hybrid Motor

I doubt that 2kW at 6.5 knots is correct.

Here is some data straight from the horse's mouth:

http://oceanvolt.com/create-energy-while-sailing

According to the chart provided by OceanVolt, a boat speed in excess of 9 knots is required to generate 1000 watts. (For a single motor, so 2kW on a catamaran.)

Still, that's not bad at all.

- Fabian
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Old 17-11-2016, 21:47   #371
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Jim,

If there is a loss, it is (apparently) not showing up on either Coleman's instruments onboard either on his test sails across the Atlantic, or this Vendee Globe, according to him. It was a primary issue for him deciding on the OceanVolt.
They may not be noticing the loss of speed, but it obviously must exist. If there really was no loss of speed, then you'd fit a few dozen of these generators, run a couple of electric motors off them, which would provide plenty of propulsion power and the excess power could be used to run house loads, aircon, etc etc...

You could also equip barges with these generators and motors, and have them run in circles connected to the grid.... free power.
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Old 17-11-2016, 21:54   #372
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
They may not be noticing the loss of speed, but it obviously must exist. If there really was no loss of speed, then you'd fit a few dozen of these generators, run a couple of electric motors off them, which would provide plenty of propulsion power and the excess power could be used to run house loads, aircon, etc etc...

You could also equip barges with these generators and motors, and have them run in circles connected to the grid.... free power.
OOhhh, I like it!!! Why don't we go into the power biz, mate... we'll make a fortune!

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Old 17-11-2016, 22:09   #373
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Re: Oceanvolt Hybrid Motor

Incredible nobody else has thought of it. Shhh!
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Old 17-11-2016, 23:38   #374
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Re: Oceanvolt Hybrid Motor

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"It's also capable of providing some electric power if necessary, but only very inefficiently.

Are you serious, or were you being ironic? The SD15 in regen mode produces 2Kw at 6.5 knots and Coleman got 4.5kW at higher speeds. That's inefficient???

Not only that, he gets no loss of boatspeed when regenerating! He has commented that his power levels from the OceanVolt SD15 is "brilliant".

The SD15 is his primary source of power. It is to be used for propulsion only in emergency, as is the case with the redundant Fischer Panda 4kW DC genset.
6.5 knots is 3.344 m/s
2000 W / 3.344 m/s = 598 N
If the turbine and generator were 100% efficient it would produce 598 N drag at 6.5 knots while providing 2000 Watts of electric power.
If overall efficiency would be 50% it would produce double drag, that is 1196 N
If it uses a normal folding propeller as a turbine, it is most likely less than 25% efficient, therefore producing at least 2400 N of drag.
245 kg mass has a force of gravity of 2400 N, in other words 3 average men together weight that much. Nowhere near a negligible amount for a racing boat of that size.

In order to get no loss of boat speed it would have to violate the laws of physics. You better sell that nonsense to someone else.
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Old 17-11-2016, 23:48   #375
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Re: Oceanvolt Hybrid Motor

OceanVolt makes the claim that their 15kW motor is equivalent to a 45 hp diesel engine, reasoning:

"The torque of the electric motors is higher than that of a diesel motor and they both have the same size propeller"

I compared the specs of the OceanVolt 15 and the 4JH45 Yanmar diesel. The Oceanvolt spins at a max 2200 RPM. The Yanmar produces about 13kW at the same RPM.

So the claim seems accurate. The OceanVolt 15 kW is roughly equivalent to a Yanmar 45 hp diesel at 2200 RPM. And 2200 RPM I guess is close to a typical cruising speed.

Of course the Yanmar goes up to 3000 RPM, which is power that the OceanVolt 15 does not have. Thus the claim that the OceanVolt will be about 1 knot slower at max speed (I assume this will vary depending on the boat).

So the question then becomes whether one needs those extra 800 RPM (and the 2x power that comes with it). I don't have enough experience, as I have never had to max out the engines against strong seas, so I don't know how important this is.

Of course one would need a 30 kW generator run these motors for any length of time...

- Fabian
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