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Old 07-05-2017, 19:23   #841
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
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.
Understand.
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Old 07-05-2017, 19:23   #842
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
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.
Because that hardwood will slow the RPM of the blade to almost zero.

IOW, this is a good Use Case for the high torque at low speed of an electric motor. It is totally irrelevant to a propellor turning in water.

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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?
Why not let an EP manufacturer answer that. How about Torquedo:

"Another commonly used motor index is the static thrust expressed in kilogram force (kf) or Newton (N). In comparison to the propulsive power and overall efficiency, this index is less meaningful, as it only measures propulsion in association with the static bollard pull experiment. In this case, as the speed is zero, the effective power (power times speed) is also zero. As a consequence to this, the static thrust does not provide any information on the propulsive power that can be actually achieved and is therefore not a meaningful index when taken in isolation."

http://torqeedo-belux.com/technologie/Torqeedo%20Propulsive%20power%20and%20overall%20ef ficiency.htm
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Old 07-05-2017, 19:45   #843
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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?
Are you saying that 8kW can drive the same prop in the same conditions at nearly twice the speed that 30kW can (regardless of where that power is coming from).
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Old 07-05-2017, 19:47   #844
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Re: Oceanvolt Hybrid Motor

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Understand.

Knowing that we have only 8kW available in this case. You are saying that I will never reach 2250 RPM since the Yanmar deliver 12kW at 2250RPM? Or is it 30kW at 1400 RPM as mentioned before?
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Old 07-05-2017, 19:56   #845
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Re: Oceanvolt Hybrid Motor

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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?


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?
If you replace only the diesel engine with Oceanvolt, but keep the gear ratio, my guess would be 4,4 ... 5,0 knots, but it of course depends on exact drag/speed relationship of the said boat. It must be very heavy and draggy to go so slow with the original diesel. I have been on a 9,4m boat with 9 hp going 7,0 knots in calm conditions with no current. 3,22 gear reduction and 15x13 prop, boat weight 4 tons with fin keel.

If you also replace the gear reduction, OV does not have the power to rotate the original prop with 2250 RPM at the propshaft, not even close.
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Old 07-05-2017, 20:00   #846
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Re: Oceanvolt Hybrid Motor

Attention OceanVolt: to build credibility, please equip two identical small sailboats w standard diesel and oceanvolt deisel/hybrid for same day, real world comparisons. This would help so much to manage speculation and varying claims/counter-claims. Couple of 35 foot monohulls would do.
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Old 07-05-2017, 20:04   #847
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Claude-D View Post
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
You are still mixing existing statements regarding props used as a turbine with imaginary statements about Oceanvolt efficiency. I'm sure you know OV produces neither props, nor turbines, only the rest of the propulsion system. The idea that the overall system could have good efficiency while regenerating with a standard marine propeller is false. It makes no difference who made it or design it, only that it has a propeller instead of a turbine that is needed to make the efficiency low.

If you consider how a fully battened mainsail function while beating to windward with all the battens inverted, you will realise why that is so. Prop as a turbine is exactly that. Guaranteed stall at the leading edge in both. And fluid flow not reattaching. How well OV makes electrical and electronic parts has no effect on this.
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Old 07-05-2017, 20:08   #848
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Claude-D View Post
Knowing that we have only 8kW available in this case. You are saying that I will never reach 2250 RPM since the Yanmar deliver 12kW at 2250RPM? Or is it 30kW at 1400 RPM as mentioned before?
Crankshaft or prop? Gearing. I thought you would have understood the difference by now.
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Old 07-05-2017, 20:38   #849
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
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.
It's already been explained. You can fit a prop to a 10 HP motor that would produce huge statics thrust. A big diameter, big blade area, very low pitch prop will do this.

And it would perform well in your tractor pull contests that seem to impress you so much.

It would also be excellent for marina manoeuvres. But it would be near useless for propulsion.

And yet again I ask: if one electric kilowatt is worth two diesel kilowatts, why not use an electric motor to power the generator?
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Old 07-05-2017, 20:45   #850
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Re: Oceanvolt Hybrid Motor

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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.
Now, this is a classic case of confirmation bias that you are constantly harping on about. You do not understand the math, nor have you tried to, but you are more than ready to pose an opinion as to the implied outcome. If you had bothered to study the papers in question you would have found that STATIC THRUST involves the displacement of water past the props with boat stationary and the DYNAMIC THRUST involves the propulsion of the boat through the water and is strongly affected by the characteristic of the resistive force presented i.e. the characteristics of the boat. To say that the difference is 0.9 is as ridiculous as saying that the ultimate solution to life is 14. If you had bothered to study the math you would have found that the relationship is heavily non-linear.

The papers in question refer to idealistic characteristics, and so in reality we have to leave it to the marine engineers to identify the correct propulsion equation. One assumes that they can do the math.

As a guideline however, you have unwittingly provided a real world example of Kato 1 vs Kato 2, which are very similar designs but different weights, Kato 1 having diesel motors and Kato 2 having EP motors. Simple calculations show that if Kato 2 were equipped with 45HP diesel motors one would expect motor speeds of 10-12 knots, but with 15Kw EP motors you get 6 knots. Remember, that the HP/KW equation vs hull speed is non-linear as well. Thus real world data indicates that OV15KW provides nowhere near the equivalent thrust of a 45HP diesel. I will grant you that the EP motor provides more thrust than predicted from the conversion from Kw to HP but not a great deal more. I accept that if I were to equip 30Kw EP to the Helia it MAY be ok but 40Kw would be my preference.

Following this line I would expect that if you were to equip 15KW EP to your Freeflow you would get about 4kn cruising speed. If I were you I would look at 30Kw which should give you similar results to typical production cats.
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Old 07-05-2017, 20:53   #851
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Re: Oceanvolt Hybrid Motor

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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.
One example - SV Curiosity (Winns) - they're running AC on Lithium batteries only and seem very rarely using genset. Another example - Sunreef 62 on the market right now with 68kWh battery. It's specifically modified to be able to run AC overnight without noise.
Yes, one would need "a little" more than 1kW solar to keep batteries charged. More like 10-15kW, I would say. Maybe, couple wind generators. During sailing power is also generated by regeneration, as widely discussed above.
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Old 07-05-2017, 20:59   #852
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Re: Oceanvolt Hybrid Motor

15 kw of solar requires about 75 square metres. Think about it. That's 10m X 7.5m. About the entire horizontal surface area of a 40 foot cat.
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Old 07-05-2017, 21:06   #853
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
Crankshaft or prop? Gearing. I thought you would have understood the difference by now.

Ok, let me try again. The maximum that can be delivered from the Oceanvolt AX8 is 8kW, maximum 2250 RPM, gear reduction 2.46:1

The Yanmar 38hp give a maximum speed of 6.7knots. The reduction is 3.4:1 I think.

So the question is what will be the maximum speed for the Oceanvolt? Using the same Propeller.

You believe that the Oceanvolt cannot reach maximum RPM in that situation? As the Yanmar deliver 12 kW at 2250 RPM. And Yes we do have to adjust for the difference in reduction gear.
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Old 07-05-2017, 21:20   #854
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Re: Oceanvolt Hybrid Motor

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Ranchero Said

Yes, one would need "a little" more than 1kW solar to keep batteries charged. More like 10-15kW, I would say. Maybe, couple wind generators. During sailing power is also generated by regeneration, as widely discussed above
Wow, 10-15Kw of solar to save $1.50 per hour to run the genny. Just shows you need a lot of greenbacks to be green.
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Old 07-05-2017, 21:39   #855
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Re: Oceanvolt Hybrid Motor

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Attention OceanVolt: to build credibility, please equip two identical small sailboats w standard diesel and oceanvolt deisel/hybrid for same day, real world comparisons. This would help so much to manage speculation and varying claims/counter-claims. Couple of 35 foot monohulls would do.
There are a few already around. Our problem is that we have not talked about it enough... You may like to have a look here: Monohull Archives - Oceanvolt
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