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Old 27-12-2017, 16:43   #961
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
So are you claiming 9kW output at 12kn with little to no drag?
Little, not no. Of course it causes drag and slows the boat> The question is "how much slower?" I'm claiming from talking at length to Oceanvolt owners with the regular regen, not even the new Servoprop, which is WAY more efficient by the way, that the slowing of the boat when you flick it from regen to off, then back on, and off etc. is very low, and by low they say it is, maybe, a quarter knot. Even if it is half a knot slower, I could care less given the huge advantages of having that much power, especially in extended cloudy periods or passagemaking at night.

And little is a relative term, as in not precise. What's little to me on my cruising cat, might be "not so little" to a racer in lighter conditions. But then he wouldn't be trying to regenerate in light conditions would he? He's RACING.

This made up hypothesis that it causes "large" drag ( there's another imprecise term for you) is understandable to some extent, because we're conceptually Ok with the drag difference between fixed 3 blade props versus feathering props, aren't we? So, the Servoprop seems counter-intuitive. I get that, but arguing from the viewpoint of personal incredulity doesn't help.

I'd be interested to ask what would be your expectation of how much the Servoprop would/should slow a somewhat performance/cruiser cat sailing at between 6 to 7 knots, according to your viewpoint?
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Old 27-12-2017, 16:47   #962
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Actually, no. It has very little drag. Not NO drag, but very little. On a cruising cat sailing at 6 to 7 knots, with BOTH Servoprops in regen mode, you MIGHT see a quarter knot difference, if you can measure a quarter knot. I spoke to an owner recently who saw no difference whatsoever, but what would he know? He only had 3 different GPS units.

But to understand why, you'd have to understand how the Servoprop works, and I do understand you don't really want to know or to understand. Not like those judges at METS who gave it the DAME award, and who actually try and understand the technology before giving out awards like DAME.

It's all been explained before on CF, but I suspect you already knew that.
You can't change physics.

It is very possible users don't see much difference. That means they are overpowered to begin with. So instead of wasting power trying to climb your bow wave, you produce power. You can bet as soon as the wind speed matches the power needed to reach hull speed, you will notice the drag, in a big way.
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Old 27-12-2017, 18:52   #963
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Re: Oceanvolt Hybrid Motor

Reversing the equation: So if we were sailing along at 11 knots and we turned on the motors and throttled up until they were delivering 9kw total to the props the boat speed would only go up 0.5kn? Seems kind of far fetched to me.
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Old 27-12-2017, 19:45   #964
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Re: Oceanvolt Hybrid Motor

Guys, the answer was given in Post #910, in the data, measured data from the 66' cat with OV SD15 during the sea trials. Those are the actual numbers.

You guys love math and physics, right? Ok, here goes.

For this boat, the power needed to motor at 10 knots is 71.5kW. Whether it comes from the sails or electric motors or diesels doesn't matter. It is what is needed to overcome the resistance of 7,225 Newtons of water resistance. Ok?

Notice how little extra speed you get from 8.4 to 10 kts from the extra 40kW of juice from the batteries? You get that?

So, they got a measured 1 to 1.2 kW regen when sailing at 10kts. When sailing, Kato still needed 71.5kW of wind force to achieve 10 knots. Right? Same boat, same resistance. Simple physics right? Speed-Resistance-Power relationship.

So when on regen, we subtract the 1.2 kW of regen "drag" from the sail power and we get 71.5 - 1.2 = 70.3kW still pushing the boat. Right? That's 1.7% less sail force pushing the same boat same water resistance. So you guys reckon the boat will now slow down "in a big way" or like a 9.9HP in full reverse???? Get real.

An analogy to help with your conceptual blockage: how much slower would you go if you reduced WOT throttle on your diesels by 1.7% less fuel flow? For 45HP diesels thats about 0.4 liter per hour on 25 liters per hour WOT fuel useage.

That's what I thought.....
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Old 27-12-2017, 22:20   #965
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Re: Oceanvolt Hybrid Motor

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Guys, the answer was given in Post #910
Thank you, BigBeakie!
But to be fair, we now need to look at this with 4500 Watts hydrogeneration power due to ServoProp. With this, you end up with 6.3% power loss at 12 knots (looking at one prop only).
But because this is a lot of energy, you would probably not need to do this for long time during the day and further I guess it can be regulated to the amount you like. So where is the problem, guys? For me its only the price.
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Old 27-12-2017, 23:10   #966
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Re: Oceanvolt Hybrid Motor

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Thank you, BigBeakie!
But to be fair, we now need to look at this with 4500 Watts hydrogeneration power due to ServoProp. With this, you end up with 6.3% power loss at 12 knots (looking at one prop only).
But because this is a lot of energy, you would probably not need to do this for long time during the day and further I guess it can be regulated to the amount you like. So where is the problem, guys? For me its only the price.
I don't think you can just say you get 6.3% loss, because it depends on the boat. I don't have the data on what the power required is for Kato to go 12 knots, so how can you say it's 6.3%? I think you took 4.5 divided by 71.5, but this is not correct. Make sense?

At 10 knots, the Servoprop curve shows just under 3kW generated (say 2.9kW), so for Kato and her resistance- power curve, that yields 71.5-2.9=68.6kW net sail force. And 2.9/71.5=4%

The thing to remember however is that the Servoprop will get the energy back into the battery much faster, and it will do it at a much lower boat speed.

So for instance Conrad Coleman used regen from his SD15 about 45 minutes a day to meet his daily power requirements. With the Servoprop in the next Vendee Globe, he might only need to regen for 15 minutes with the Servoprop, which might suit him better re weather or sea state conditions. One thing is clear, the reliance on gensets for battery charging while sailing will be looked at very closely by ocean racers from now on. As they say, watch this space.
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Old 28-12-2017, 00:45   #967
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Re: Oceanvolt Hybrid Motor

Quote:
At 10 knots, the Servoprop curve shows just under 3kW generated (say 2.9kW), so for Kato and her resistance- power curve, that yields 71.5-2.9=68.6kW net sail force. And 2.9/71.5=4%
Are you saying that when generating 3 kw of electrical power, this prop only detracts 3 kw from the energy driving the boat (sails in this case)?

That's 100% efficiency in converting hydraulic flow to rotational torque, and torque to electricity and electricity to energy stored in a battery.

Somehow this seems optimistic to me.

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Old 28-12-2017, 00:57   #968
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Re: Oceanvolt Hybrid Motor

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I must have gone to the wrong university. I learned that someone trying to sell something should explain how their product is useful with clear specifications and costs so anyone can compare it with a competitive solution. I should not have to “dig” for the data.
Sorry but I'll have to side with the oceanvolt marketing department here.

What you say is true but only if you came up with the proverbial "better mouse trap".

If you are selling an inferior product, the goal of the marketing department is to confuse and distract with vague claims and misleading (but technically not incorrect) information while putting out flashy displays.
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Old 28-12-2017, 01:31   #969
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Jim Cate View Post
Are you saying that when generating 3 kw of electrical power, this prop only detracts 3 kw from the energy driving the boat (sails in this case)?

That's 100% efficiency in converting hydraulic flow to rotational torque, and torque to electricity and electricity to energy stored in a battery.

Somehow this seems optimistic to me.

Jim
Yes, well we're not being precisely accurate because there are losses, particularly in the last stage of battery charging. But it does assume Lithium battery tech. But the other percentages are in the high nineties, so it's close enough to be very practical.
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Old 28-12-2017, 03:54   #970
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Re: Oceanvolt Hybrid Motor

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That's 100% efficiency in converting hydraulic flow to rotational torque, and torque to electricity and electricity to energy stored in a battery.
Yes, you are probably right and I missed this.
We have to assume that the hydrodynamic efficiency of the adjustable prop is may be 25-60% (?). The electric losses down to the battery are relatively small.
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Old 28-12-2017, 05:05   #971
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Re: Oceanvolt Hybrid Motor

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Originally Posted by myocean View Post
Yes, you are probably right and I missed this.
We have to assume that the hydrodynamic efficiency of the adjustable prop is may be 25-60% (?). The electric losses down to the battery are relatively small.
I dunno the actual figures of overall efficiency, all I know is the speed vs regen output as actually measured. These are from both tank testing and test boats where the Servoprop has been in test for over a year prior to the official production launch at METS this year. One of the test boats was a Swan 50 I believe.

So for me, the question of what are the losses, how efficient is this aspect or that aspect, I couldn't really care less. It's a bit like that saying about mathematical models i.e. no models are accurate, but some models are very useful. The Servoprop will be very, very useful.

As long as I can head out for a sail with the Servoprop when my solar output is low due to several days of heavy cloud, rain etc. and I need to top up the bank, I'll be very happy to have as much battery charging as a fair size diesel genset as we sail along. That is a game changer.
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Old 28-12-2017, 05:09   #972
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Re: Oceanvolt Hybrid Motor

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Yes, well we're not being precisely accurate because there are losses, particularly in the last stage of battery charging. But it does assume Lithium battery tech. But the other percentages are in the high nineties, so it's close enough to be very practical.
I believe it hurts the perception of hybrid electric systems to make claims that are obviously wrong on their face. One can't just brush away the issue of efficiency as if it's too small a detail to make a difference. It would be groundbreaking if the conversion efficiency of sail power to battery stored usable energy was even 50%. If one could sail giving up only 5kW of sail power for one hour and be able to use 2.5kW of that power later for an hour would be amazing. A 1,000W solar panel array would require probably 4-5 hours to produce similar amounts of usable stored energy. Solar is the true competition for cruiser's attention not W&S.
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Old 28-12-2017, 05:16   #973
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Re: Oceanvolt Hybrid Motor

What claim is wrong?


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Old 28-12-2017, 05:38   #974
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Re: Oceanvolt Hybrid Motor

Oceanvolt only seem to sell complete solutions including batteries, charger etc.

A 10 kw system containing 10kw of batteries, servprop etc cost 31 000 Euro.
A little bit to much for me but an awesome system!
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Old 28-12-2017, 05:55   #975
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Re: Oceanvolt Hybrid Motor

The sails have to produce X horsepower to move the boat at the desired speed, let's assume hull speed (HS).

If the sails produce X+, the extra power is typically wasted by trying to push the boat up it's bow wave. Since climbing your bow wave takes a huge amount of power, OV is taking that extra power and using it to produce electricity.

But if the sails are only producing X, the drag produced by the OV will be huge.

It's a good idea, but it's not free.
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