Oceanvolt Hybrid Motor

[44'cruisingcat]

So a 20 hp electric motor is actually more powerful than a 45 hp diesel, is that what they're claiming?


This is very interesting. If true, why would you use a diesel to power the genset? For instance, if it takes a 40kW diesel to power a 30kW genset, why wouldn't you use a (more powerful) 20kW electric motor, and get the excess 10kW free?

[cwjohm]

Originally Posted by BigBeakie

Ok, the argument for a 15kW Serial Hybrid OV SD15 is that when you rip out a 45HP diesel engine and put in the SD15, the OWNERS say it is about the same, and is in fact superior in some respects. It is better for making headway against wind and tide. It is better for docking in the wind. On DC genset, it uses less fuel at cruising speed. They use regeneration alot and most of their motoring is from regen into the LFP bank. What can I say? The story sounds compelling, and then there are those here that say it just ain't so. But the fact is not a single owner has replaced their OV SD15 system. That;s quite unlike your examples, isn't it? I will have data soon enough to put forth the objective case. I know you are not planning to convert just yet, so be patient.

So, where are these owners who claim this. Nobody I have spoken to and nobody on CF.

With most yachts now you get an option of a standard diesel or a larger diesel. Having chosen the standard it would be an unusual event for an owner to cover the cost of an upgrade. They will live with the consequences. Similarly, with an undersized hybrid system nearly everybody would live with the limitations imposed rather than put diesels in. This is what I believe your OV SD15 owners are doing and what I believe you will do. I think it stretches credibility to think that faced with the consequences of lower cruising speeds and travel limitations of avoiding bad weather events you will replace your hybrid with diesels. It will however, make you think very carefully about significant ocean passages.

In fact I think you will be very happy with your system. Having spent the money on 2 OVSD15 motors, a milspec 30Kw generator, and 30KW of Lithium Battery Bank investment bias will give you no choice on the matter. You will simply justify the limitations as you have no other choice and laud the advantages. The general cruising community however, will remain circumspect until such time as these limitations are ameliorated, as they are not inclined to spend significant extra funds for lesser performance.

However, there are many instance of those with the financial means, removing these systems and replacing them with diesels as they are not prepared to suffer the constraints involved.

[cwjohm]

Originally Posted by 44'cruisingcat

So a 20 hp electric motor is actually more powerful than a 45 hp diesel, is that what they're claiming??

No, they are claiming that a 20hp electric translates to greater thrust at the prop. equivalent to a 45hp diesel by a process of magic rather than physics.

As with all spin there is some element of truth in that an electric motor will result in a more manouverable system due to the linear torque curve, in that at lower than rated hp the electric motor will deliver more thrust. They then extend this to say that at maximum rated power the electric motor will deliver more thrust, this being a nonsense argument from extrapolation.

[BigBeakie]

Originally Posted by cwjohm

No, they are claiming that a 20hp electric translates to greater thrust at the prop. equivalent to a 45hp diesel by a process of magic rather than physics.

As with all spin there is some element of truth in that an electric motor will result in a more manouverable system due to the linear torque curve, in that at lower than rated hp the electric motor will deliver more thrust. They then extend this to say that at maximum rated power the electric motor will deliver more thrust, this being a nonsense argument from extrapolation.

Ok, now we are getting somewhere. But instead of stating that at maximum rated power we claim that it delivers MORE thrust, which I don't think I have ever claimed, let's just look at the known physics (as you and others are so fond of doing) of torque, RPM and propellers. And which is perfectly rational, and is what I have been trying to genuinely sort out from the beginning.

So let's look at the torque curve vs RPM of the SD15 motor, or any other that we have data on such as that was posted by StuM on the Torqeedo 30kw, and the torque curve of a diesel of double the kW rating. And lets even assume exactly the same propeller, for the moment.

Isn't that what this all boils down to? And there are others here who are eminently more qualified to do that than I am, cuz I am no engineer. (Actually my wife is an engineering graduate of the French equivalent of MIT, and keeps me honest & real on this evaluation of Serial Hybrid EP.)

Now we know that the propeller is directly coupled to the electric motor so the RPM of the motor is pretty much what the RPM of the propeller is. Right?
And we see that the torque expressed in Nm of the electric motor is STUM's post is AT LEAST double ( sometimes triple as per StuM post #493 Torqeedo 30kW 350 Nm, diesel 38kW 105Nm ) the diesel engine. And we know that the diesel engine will stall at low RPM if there is not a transmission system with gear ratios that allows it to turn the prop. So the RPM of the PROP is NOT the same as the RPM of the crankshaft. Right?

So given all that, and the fact that the prop couldn't care less what was turning it as long as when it is under resistance load it has enough grunt, ie torque, to turn it, then where does that leave us? The OV SD15 has max RPM of 2,200 and flat torque curve of about 290Nm. The new Yanmar 4JH5CE saildrive 45HP does not even show torque until 1600RPM (does anyone have those figures, out of interest?) and then it is nice and flat to 1800 RPM at 155Nm, where it starts to drop steadily so that at 2,200 RPM the torque produced is 150Nm (about half the OV SD15, right?) and it continues to drop until at WOT it is 125Nm.

See: http://www.yanmarmarine.com/theme/ya...chure-SD60.pdf

To complete the analysis I need the propeller RPM of this Yanmar engine at the various crankshaft RPM's. Then, and I believe only then, can we settle this argument. Am I wrong? Can anyone help provide those prop RPM's for the diesel engine? I guess I can get them from Power Equipment.

One thing is for sure though, I'm pretty sure that at 2200RPM on the Yanmar, the prop is not turning at 2200RPM. But the prop on the OV SD15 is. So if the props on the 2 systems is the same (about 16 x11 I'm guessing?) which produces more thrust?

[BigBeakie]

Sorry, the gear reduction ratio was right there on the Yanmar SD60 spec sheet at 2.49, so at 2200 RPM (crankshaft) the diesel prop is spinning 2200/2.49 = 889 RPM. Right?

At WOT of 3,000 crankshaft RPM the prop is spinning 3000/2.49 =1200 RPM.

The SD15 is spinning at 2200 RPM at full power. And at about half power i.e. at say 1,000 RPM the SD15 is still spinning the same prop at about what the 45HP/33kW diesel is at WOT. In fact, it can spin an even bigger more aggressively pitched prop, but cruising speed suffers, same as a diesel.

So here is my confusion. If the SD15 can spin the same prop (or bigger) at higher prop RPM's, doesn't that mean it can produce higher thrust?

But we don't want to run it at full power because the kW usage is disproportionately high. So run it around half or even lower, and get almost the same speed.

Which is, in fact, what I am hearing from owners who are using them for cruising. I am also hearing that when pushing into higher winds, their OV Sd15 Hybrid boat does not seem to slow down and speed up in the seaway, but moves more constantly forward.

Is this magic, or is this physics? If I am wrong, please educate me.

[transmitterdan]

There is an easy way to prove that full on diesel electric is less efficient than a plain mechanical system at cruising speed. What do most of the hybrid car manufacturers do? At cruise they lock the main IC engine to the wheels via a transmission. Toyota does that and I think most others do too. The main improvement in fuel efficiency for a hybrid auto comes from stopping the engine at stops, regenerative braking and the high electrical torque starting from a standing stop. It does not come from using electricity to drive the wheels at cruising speed. If it were so they would have no transmission at all since it just adds weight and cost.

[StuM]

Yanmar SD20 sail drives at generally geared at 2.64:1 so at 2200 RPM, the prop is turning at 833RPM. At 3200, it's 1,212 RPM. And of course, as you gear down, the torque at the prop goes up .

A 16 x 11 prop turning at 2200 RPM for a displacement hull motoring at typical cruiser speeds will be very inefficient regardless of whether it is EP or Diesel driving it.

[BigBeakie]

Originally Posted by transmitterdan

There is an easy way to prove that full on diesel electric is less efficient than a plain mechanical system at cruising speed. What do most of the hybrid car manufacturers do? At cruise they lock the main IC engine to the wheels via a transmission. Toyota does that and I think most others do too. The main improvement in fuel efficiency for a hybrid auto comes from stopping the engine at stops, regenerative braking and the high electrical torque starting from a standing stop. It does not come from using electricity to drive the wheels at cruising speed. If it were so they would have no transmission at all since it just adds weight and cost.

Yes, you could be right about that. But I asked the question before, is efficiency really all that important when your fuel price is low? To continue your non boat example, do the people using LPG in their gasoline engines cars, like taxis, care that it is marginally less efficient than gasoline/petrol? No, they do not, because the differential between the loss of mileage using LPG and the cheaper price of LPG is way in favour of the cheaper price. I do alot of miles on my LPG Pajero 4x4, and the payback was so quick it was amazing. That was over 225,000 km ago and we have saved significant $$$ in the meantime.

Similarly, I am saying that by far the bulk of cruising motoring hours can be done off the LFP bank which is charged MOSTLY, by solar and regeneration while sailing. Only when you need to do extended motoring for many hours to days on end, do you need to use the DC Genset to charge the batteries to feed the EP.

And in the worst case scenario, even assuming using the diesel genset is not as "efficient" as using diesel propulsion engines, i.e. marginally less distance traveled per liter of diesel fuel used, it is proportionately a low percentage, and the other benefits of Serial Hybrid EP outweigh that occasional "inefficiency".

[StuM]

Originally Posted by BigBeakie

Now we know that the propeller is directly coupled to the electric motor so the RPM of the motor is pretty much what the RPM of the propeller is. Right?

I am amazed that with all of the research you have done on Oceanvolt and all the performance data that they have supposedly given you, that you are not aware of this little fact, straight from their website:

SD - ELECTRIC SAIL DRIVE MOTORS

Reduction Ratio: 1.93:1

[StuM]

To follow up on my last. Using OV's own figures:

OV SD15. Using all 15 kW (20HP) of output, max RPM of 2200 and a 1.93:1 gearing, max prop speed is 1,140 RPM.

Yanmar 3JHJ3 diesel and SD 20 with a 2.64:1 ratio:

3JHJ3. Max HP = 38 @ 3800 RPM.

Prop speed 1,140 requires an engine RPM of: 3000

At 3000 RPM the 3JHJ3 is running at the 80% WOT sweet spot and using about 18HP (13.5kW) and I still have 800 RPM and half my available HP in the bank in case I need it.

I think that finally puts to rest the notion of "magic electric HP".

[FlyingScot]

Originally Posted by transmitterdan

There is an easy way to prove that full on diesel electric is less efficient than a plain mechanical system at cruising speed. What do most of the hybrid car manufacturers do? At cruise they lock the main IC engine to the wheels via a transmission. Toyota does that and I think most others do too. The main improvement in fuel efficiency for a hybrid auto comes from stopping the engine at stops, regenerative braking and the high electrical torque starting from a standing stop. It does not come from using electricity to drive the wheels at cruising speed. If it were so they would have no transmission at all since it just adds weight and cost.

I've owned 3, still own 2 Honda hybrids, well my teenagers do. All manual transmissions so not the same as Toyota and many other hybrids. Honda uses an electric motor as part of the crankshaft, or inline with the crank. Extra torque via 12vdc power as needed. This allows for a smaller engine. Smaller engine is more efficient. Honda always sneaks in other things to add to the mpg. Lighter construction, lower drag (CD), twin plug per cylinder head, lean burn capable at 23.1 a/f lowering pumping losses, regen braking etc. So you can't always narrow it down to one single item.

But is a diesel putting out 30kw more efficient than two at 15kw each? Keeping it simple on this point and not arguing that electric HP better or same as diesel HP.

Chris

[StuM]

Originally Posted by BigBeakie

Sorry, the gear reduction ratio was right there on the Yanmar SD60 spec sheet at 2.49, so at 2200 RPM (crankshaft) the diesel prop is spinning 2200/2.49 = 889 RPM. Right?

At WOT of 3,000 crankshaft RPM the prop is spinning 3000/2.49 =1200 RPM.

The SD15 is spinning at 2200 RPM at full power. And at about half power i.e. at say 1,000 RPM the SD15 is still spinning the same prop at about what the 45HP/33kW diesel is at WOT. In fact, it can spin an even bigger more aggressively pitched prop, but cruising speed suffers, same as a diesel.

So here is my confusion. If the SD15 can spin the same prop (or bigger) at higher prop RPM's, doesn't that mean it can produce higher thrust?

But we don't want to run it at full power because the kW usage is disproportionately high. So run it around half or even lower, and get almost the same speed.

Which is, in fact, what I am hearing from owners who are using them for cruising. I am also hearing that when pushing into higher winds, their OV Sd15 Hybrid boat does not seem to slow down and speed up in the seaway, but moves more constantly forward.

Is this magic, or is this physics? If I am wrong, please educate me.

OK, lets take it down to your 1000 RPM which you claim is "half power" for the OV SD15. AT 1.93:1 that's a prop speed of 518 RPM.

For the same prop speed, the 3JH3 with SD20 @ 2.64:1 will be turning over at 1365 RPM. which is just above idle speed, will use less than 2 diesel HP.

(I had to modify my spreadsheet to work that out because I've never bothered to calculate power/fuel consumption that low before)


So once again the OV SD15 at "half power" is doing what my diesel does at idle.

You can talk all you want about "low end torque" etc - but you only need enough to turn your propellor at your desired RPM, any more is wasted.

[BigBeakie]

Originally Posted by StuM

I am amazed that with all of the research you have done on Oceanvolt and all the performance data that they have supposedly given you, that you are not aware of this little fact, straight from their website:

SD - ELECTRIC SAIL DRIVE MOTORS

Reduction Ratio: 1.93:1

Thanks StuM You shouldn't be surprised, I did miss this gear reduction! This morning I was reading about electric motor applications and it talked about direct coupling to the shaft. In my mind I transposed that to my post, a big booboo!!

I am, freely admitted, pretty new to this propulsion stuff, and just coming to grips with understanding the issues around propeller efficiencies, reduction ratios etc. I'm sure I will make other errors down the track, that's what these forums are good for.

Ok, so the magnitude of the difference is considerably less than the figures I gave before, but it seems the principle is the same. Would you agree?

On the new information the full power SD15 at 15kW spins the prop at 2200/1.93 = 1,140 RPM and the 45HP/33kW at WOT spins it at 3000/2.49 =1,205 RPM, so pretty close. But at that RPM the SD15 torque is 190Nm and the 45HP Yanmar is 125Nm.

Isn't that significant? Wouldn't the SD15 be capable of producing more thrust?

[StuM]

Originally Posted by FlyingScot

But is a diesel putting out 30kw more efficient than two at 15kw each? Keeping it simple on this point and not arguing that electric HP better or same as diesel HP.

Ah, there's the rub! We've discussed this one recently on another thread.
The answer is, it all depends on the circumstances.

http://www.cruisersforum.com/forums/...es-176373.html

[StuM]

Originally Posted by BigBeakie

...
Ok, so the magnitude of the difference is considerably less than the figures I gave before, but it seems the principle is the same. Would you agree?

On the new information the full power SD15 at 15kW spins the a prop at 2200/1.93 = 1,140 RPM and the 45HP/33kW at WOT spins it another prop at 3000/2.49 =1,205 RPM, so pretty close. But at that RPM the SD15 torque is 190Nm and the 45HP Yanmar is 125Nm.

Isn't that significant? Wouldn't the SD15 be capable of producing more thrust?

Thrust is the result of more than torque.

What 45HP engine, sail drive and prop size are you referring to? See my figures above for my 3JH3. If the engine is using 45HP to turn the prop at 1205 RPM, it must be a very large/coarse pitch prop. The OV SD15 would not be able to produce enough power to turn that same prop at the same speed.

BTW, you are comparing the wrong torque numbers. Cranskshaft torque is not the same as prop shaft torque once you step through a gearbox. That's the whole point of gearing, as it reduces RPM, it increase torque - and vice versa.