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Old 07-05-2017, 13:48   #826
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Claude-D View Post
Yes, your calculations are correct and yes, the percentage of slip is more for electric motors than diesel inboard engines. This is because of the greater torque of the electric motor.
No, slip has nothing to do with greater torque.
>200 meters long containerships can have massively more torque, yet less slip and better efficiency than the prop in the conditions you described. too much slip is about overloading disc area.
"Slip, in fact, is actually required to produce thrust."
That is correct. But less slip can produce the same thrust at the same speed in the same boat more efficiently, if propeller disc area is increased.

Quote:
However, "propulsive efficiency" is to move the power from your batteries to your propeller efficiently.
No it's not.
propulsive efficiency is to move power from rotating shaft into propulsive power. Torque times angular speed into thrust times boatspeed.
Also, propulsive efficiency < (1 - slip) for all propellers used as one, not as a turbine. You can find that formula from every book about propellers, including the well written one you quoted.

Quote:
That is; How much power do you require to push a boat at a given speed versus how much power are you drawing from the batteries. (or from your diesel fuel).
That's total efficiency, if the drag of the given boat is defined and known.

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I am not sure that I am following. Are you saying that the Oceanvolt are not very efficient in hydro-generation mode?
No, I'm saying the prop used in KATO is not very efficient when used as a turbine in those conditions, and that applies to almost all marine propellers.
That has nothing to do with Oceanvolt, except it uses a prop, not a turbine. If you would change OV to another system using the same prop, no major improvements could happen for regeneration efficiency.

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Surely if we the system was 100% efficient in Hydro-generation mode, the boat will stop!!!
Wrong conclusion. If the systems takes out just one watt from the fluid flow and manages to put it all into torque of the rotating shaft, it would be 100% efficient, and has almost no effect at all on the boat speed. In the real world that will never happen, as no system has 100% efficiency.

In order to stop the boat you would need more power in regeneration regardless of the level of efficiency.
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Old 07-05-2017, 13:54   #827
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
1800-2550 Prop shaft RPM with a 16.5 X 11 prop? Really???
No, just 2250 rpm.
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Old 07-05-2017, 14:47   #828
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ranchero76 View Post
For you - it doesn't make sense.
Let's see. Having electric propulsion also means some benefits when not cruising, in form of huge solar/battery bank which MUST be installed so things start making sense.

Now picture - not you, but other group of cruisers, who like and appreciate some basic comfort.
Now let's count. Let say - 6 friends cruising. Electric propulsion. It's just small part of energy consuming, as it's not happening everyday. Plus one or two hot showers per day for 6 persons. Cooking for 6 persons (electric stove, cook top etc.). Water maker. Laundry for 6 persons. Air condition anytime when it's desired. Dehumidifiers. Dive compressor. Entertainment system, laptops, tv, etc. Electric tools. ALL of that will run from same batteries, which on cruising days used mostly for propulsion.
If there's enough energy collected in batteries during sailing - without hesitation use EP when wind is weak, even go directly against wind to save time and mileage, etc, etc.

Now - how much fuel and noise will it take to generate this amount of energy on regular boat with diesels, genset and small 1kW solar array? I bet - a lot more than $1000, plus all that noise.
The solar and batteries won't support those "basic comforts". The genset would need to be used anyway.
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Old 07-05-2017, 14:48   #829
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
No, slip has nothing to do with greater torque.
>200 meters long containerships can have massively more torque, yet less slip and better efficiency than the prop in the conditions you described. too much slip is about overloading disc area.
"Slip, in fact, is actually required to produce thrust."
That is correct. But less slip can produce the same thrust at the same speed in the same boat more efficiently, if propeller disc area is increased.

No it's not.
propulsive efficiency is to move power from rotating shaft into propulsive power. Torque times angular speed into thrust times boatspeed.
Also, propulsive efficiency < (1 - slip) for all propellers used as one, not as a turbine. You can find that formula from every book about propellers, including the well written one you quoted.

Yes it is... (feels like Monty Python .... ) And if we want to be pedantic with definitions, this is what you will find if you just Google it .... "overall propulsive efficiency
η\eta is the efficiency, in percent, with which the energy contained in a vehicle's propellant is converted into useful energy, to replace losses due to aerodynamic drag, gravity, and acceleration."


That's total efficiency, if the drag of the given boat is defined and known.

Yes... Total PROPULSIVE efficiency...


No, I'm saying the prop used in KATO is not very efficient when used as a turbine in those conditions, and that applies to almost all marine propellers.
That has nothing to do with Oceanvolt, except it uses a prop, not a turbine. If you would change OV to another system using the same prop, no major improvements could happen for regeneration efficiency.

Wrong conclusion. If the systems takes out just one watt from the fluid flow and manages to put it all into torque of the rotating shaft, it would be 100% efficient, and has almost no effect at all on the boat speed. In the real world that will never happen, as no system has 100% efficiency.

If the Hydro-Generation was extracting all the energy generated by the sails the boat would stop! Obviously very silly and not relevant to what we are discussing here. But, it was the point that I was making....

In order to stop the boat you would need more power in regeneration regardless of the level of efficiency.
Still, I am not following your train of thought. Are you actually saying that the Oceanvolt motors are not efficient? Or are you just wanting to contradict me, because it is definitively not an argument
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Old 07-05-2017, 15:06   #830
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cwjohm View Post
When these sorts of claims are made then rational debate becomes impossible.



.
I'd have to agree. The fact is, a kilowatt is a kilowatt. It's the product of torque and RPM.

A 15 kw electric motor produces the same power as a 15 kw diesel or petrol motor.

Yet the "electric superhorse" claims keep getting wilder. Now they're claiming electric horses are twice as big.

So I ask again, if an electric motor which consumes just 15kw produces the same power as a 30kw diesel, why not use an electric motor to power the generator? This would seem to be a logical choice, in fact the ONLY logical choice.
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Old 07-05-2017, 15:12   #831
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by Just Another Sa View Post
No, slip has nothing to do with greater torque.
>200 meters long containerships can have massively more torque, yet less slip and better efficiency than the prop in the conditions you described. too much slip is about overloading disc area.
"Slip, in fact, is actually required to produce thrust."
That is correct. But less slip can produce the same thrust at the same speed in the same boat more efficiently, if propeller disc area is increased.

No it's not.
propulsive efficiency is to move power from rotating shaft into propulsive power. Torque times angular speed into thrust times boatspeed.
Also, propulsive efficiency < (1 - slip) for all propellers used as one, not as a turbine. You can find that formula from every book about propellers, including the well written one you quoted.

That's total efficiency, if the drag of the given boat is defined and known.


No, I'm saying the prop used in KATO is not very efficient when used as a turbine in those conditions, and that applies to almost all marine propellers.
That has nothing to do with Oceanvolt, except it uses a prop, not a turbine. If you would change OV to another system using the same prop, no major improvements could happen for regeneration efficiency.

Wrong conclusion. If the systems takes out just one watt from the fluid flow and manages to put it all into torque of the rotating shaft, it would be 100% efficient, and has almost no effect at all on the boat speed. In the real world that will never happen, as no system has 100% efficiency.

In order to stop the boat you would need more power in regeneration regardless of the level of efficiency.
Quote:
Originally Posted by 44'cruisingcat View Post
The solar and batteries won't support those "basic comforts". The genset would need to be used anyway.
I am curious, So how much energy do YOU use on your boat? 1kW of solar panels will give you about 5kW a day. This equates to running your genset for how long (in YOUR boat)? Will I guess one hour? So, anyone having 1kW of solar on board, will not have to suffer the pain and expenses of running their genset for one hour every day... a good thing in my book...
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Old 07-05-2017, 15:29   #832
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Re: Oceanvolt Hybrid Motor

We have 800 watts of solar. Unfortunately we also live in the real world, where the mast and boom sometimes cast shadows, where there are sometimes clouds, and where solar panels often don't produce 100% of their rated power.

But yes, when it's sunny we can run our fridge, freezer, watermaker etc on solar. But there's simply no way it could power aircon. Not even close. And for propulsion? LOL.

Claude , did you used to work for Torqueedo? We may have met.
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Old 07-05-2017, 15:32   #833
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
No, just 2250 rpm.
Where then?

He was asked:

1) How high revs at propshaft at full power in calm conditions and what boat speed?
2) How high revs at propshaft at 23 knots while regenerating while sailing?


And he replied:
1) 2250 RPM
2) 1800-1900 RPM You can see this on my Youtube video.
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Old 07-05-2017, 15:40   #834
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Re: Oceanvolt Hybrid Motor

A question and a challenge for you guys.

If we take let say a 10M long keel monohull, fitted with a 38hP Yanmar shaft drive. Since the Yanmar can push this boat at 6.7knots at full throttle in calm water. What will be the maximum speed if we swap the Yanmar for an 8kW shaft drive Oceanvolt at 2,250 RPM. Keeping the original propeller?
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Old 07-05-2017, 15:53   #835
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Claude-D View Post
A question and a challenge for you guys.

If we take let say a 10M long keel monohull, fitted with a 38hP Yanmar shaft drive. Since the Yanmar can push this boat at 6.7knots at full throttle in calm water. What will be the maximum speed if we swap the Yanmar for an 8kW shaft drive Oceanvolt at 2,250 RPM. Keeping the original propeller?
That 38HP Yanmar will be geared to drive that prop at an efficient speed of around 1400 RPM at WOT.

Nearly doubling the prop speed would provide little gain because of decreasing efficiency, regardless of the source of the energy.

The question is: if it takes 30kW to turn that prop at around 1400 RPM, how do you turn it at 2250 RPM with 8kW?
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Old 07-05-2017, 17:41   #836
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
That 38HP Yanmar will be geared to drive that prop at an efficient speed of around 1400 RPM at WOT.

Nearly doubling the prop speed would provide little gain because of decreasing efficiency, regardless of the source of the energy.

The question is: if it takes 30kW to turn that prop at around 1400 RPM, how do you turn it at 2250 RPM with 8kW?
Ok, so are you saying that an 8 kW shaft-drive Oceanvolt does not have the power to turn the shaft at 2250 RPM on this boat?
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Old 07-05-2017, 18:25   #837
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Claude-D View Post
Ok, so are you saying that an 8 kW shaft-drive Oceanvolt does not have the power to turn the shaft at 2250 RPM on this boat?
Since the 38hp Yanmar turns 12kw @ 2250, I would say NO!
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Old 07-05-2017, 18:35   #838
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cwjohm View Post
When these sorts of claims are made then rational debate becomes impossible.



I have all that. In 3 years I have travelled up the East Coast of Aus. 3 times to Whitsundays and once around the Pacific Islands. Cost of fuel was A$1500 per year. Remember this is not the difference as in an EP system the generator will have to run often.

TCO claims are nonsense.

Yes you do not have to suffer the noise and vibration, you can pretend you are protecting the environment, and you can boast loudly at sundowners as to how you have a state of the art boat. All good reasons for EP. Financial justification is not one of them.
Chris, help me out here. You said,

[I][/When these sorts of claims are made then rational debate becomes impossible.I]

For the benefit of those reading this that may have wondered why I said this,
i.e. that I thought the propulsive thrust is about equal between the OceanVolt SD15 and a Beta 45HP diesel, it might be instructive to explain this because I understand, I really do, the skepticism of those who do not understand why EP vendors and "proponents" say such things. The reason I understand the skepticism is because when I began my journey to considerEP I too started out very skeptical. It didn't make any sense to me either, back then.

I won't go into the whole discovery journey here, but I satisfied myself that indeed electric motors of a smaller HP rating than the equivalent HP diesel, do produce more torque. So what? Well, let's cut to the chase. If you want to tturn a propshaft against resistance, whatever the resistance is such as a boats displacement through saltwater, and against wind, and against waves, well then an electric motor will maintain producing torque better than a diesel engine. Basically, that's the story a nutshell. A diesel engine will stall out before an electric motor will give up, and I satisfied myself that this is true in several different industries, not just marine engines and pushing boats. For an example the local sawmill guy explained to me why they switched over many years ago to electric motors to drive a saw because with Australian hardwoods, the diesel used to stall. When they replaced the diesel with an electric about half the kW rating, the logs did not have a chance. There were several other examples I sought out, and it was consistent that that 1 electric HP does not equal 1 diesel HP IN THE WORK THAT IT CAN DO.

But to my specific statement re 15kW OV SD15 & 45HP Beta Turbo, I spoke directly to the technical director of Beta Marine in the UK and asked what is the thrust expressed in kgf of his Beta 45 Turbo. He knew that figure ( I was impressed) at is is 320 kgf at full throttle, and that is with a 3 bladed fixed prop.

When Conrad Coleman was having his boat accepted by the technical committee of the Vendee Globe, the engines all had to pass a test of bollard pull test. The OV SD15 gave a STATIC bollard pull of 290 kgf.

So, I hear you ask, what is the relationship between static bollard pull force and actual propulsive thrust that pushes your boat against wind & waves?
Good question, and I sought that answer from multiple sources such as propeller design engineers, diesel technical resources and the technical papers written that form the basis of ship propulsion system design. I did not understand the math or even tried to, I just wanted the answer. It is about 0.9 , i.e. the static bollard value is 10% less than the propulsive thrust. Therefore Coleman's SD15 static thrust of 290 kgf is 10% less than the actual propulsive thrust so 290 x 1.1=319 kgf.

319 is pretty close to 320 isn't it?

Now, if anyone can inform me how this is dramatically wrong, fair enough.

And Chris, to me your certainty that this is not worthy of "rational debate" is not, in itself, rational. But, I'm willing to listen, so please explain exactly what is wrong with my analysis, such as it is. I am just trying to figure this out.
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Old 07-05-2017, 18:37   #839
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Re: Oceanvolt Hybrid Motor

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Since the 38hp Yanmar turns 12kw @ 2250, I would say NO!
Where are you getting these figures of 12kW @2250RPM? Is it from a publication from Yanmar?
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Old 07-05-2017, 19:08   #840
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Re: Oceanvolt Hybrid Motor

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Since the 38hp Yanmar turns 12kw @ 2250, I would say NO!
Don't confuse crankshaft and propshaft RPM to HP/kW. At 2250 crankshaft RPM, that 12kW from the Yanmar will be geared to turn the prop at less than 1000 RPM.
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