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Old 06-12-2016, 00:16   #571
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
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.
Stu,

I picked the Yanmar 4JH45 with SD60 and have no idea what prop for the purpose of this exercise just because OV say their SD15 is the functional equivalent of a 45HP diesel. And there have been all the comments here about that claim being bogus and marketing hype, and so forth.

I can say I have personally met the OV folk, and they are about as far away from sales hype types you can get IMO. And believe me I have certainly met the snake oil type....nuff said. OV seems to me to be a very technically driven company with a fanatical focus on QA. I would say quite honestly that I think marketing is NOT their strong game, never mind "clever" marketing of the hype type.

Yet the comments back to me from OV owners is that the OV SD15 is about the same as a 45HP diesel. Some of them have re-powered with OV after having diesels in their boat. I visited a new OV owner a couple of weeks ago who has removed his 38HP diesel shaftdrive with a 16x11 Kiwiprop from his Freedom 33 mono, and is putting in an 8kW OV shaft drive with the SAME Kiwiprop back on. Those 16x11 specs for the prop are exactly want was recommended by OV for their AX8 KW. He will be doing extensive testing, so that will be a good data point. I will be particularly interested to see the regeneration data for the Kiwiprop.

The OV owners opinions have to count for something. So you can see my quandry.

So let's run the numbers and see what comes up. Ok? That is all I've ever wanted to do.

I will need assistance doing that, becuz you already get the picture that I'm basically incompetent to do the technical analysis on converting crankshaft torque to propshaft torque, prop specs and loads, etc. Deal?

Let's start with what do you need to know about the OV SD15 besides the max revs at 2200 and gear reduction at 1.93:1 and torque of 290Nm, in order to compare the thrust vs any 45HP diesel of your choice? We know from the Vendee Globe bollard pull result that the OV SD15 on Coleman's boat pulled 320 kg in their static bollard pull test for 15 minutes. As I understand it, the Vendee Globe committee requirement was 280 kg for 15 minutes.

Once I know the thrust, I can closely approximate how either engine will push my cat against the wind of various strengths, which is where I want to get to. I'm sure Mr. Cwjohm would concur with that.
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Old 06-12-2016, 03:45   #572
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Re: Oceanvolt Hybrid Motor

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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
It depends as Stu said. In the range we are talking then the efficiencies would be about the same I would guess. But I think the edge would go to the two mechanical engines. A 30kW engine can produce about 20kW of electricity max with a somewhat reasonable life expectancy (that's being pretty optimistic). Since efficiency of the electrical side is about 75-80% it means we can expect to get about 8kW max to each prop. I think the 15kW diesel can beat that number while burning the same or slightly more fuel.

If you raise the hypothetical power from 2X15kW to say 2X30kW then mechanical wins hands down.
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Old 06-12-2016, 04:05   #573
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Stu,

Let's start with what do you need to know about the OV SD15 besides the max revs at 2200 and gear reduction at 1.93:1 and torque of 290Nm, in order to compare the thrust vs any 45HP diesel of your choice? We know from the Vendee Globe bollard pull result that the OV SD15 on Coleman's boat pulled 320 kg in their static bollard pull test for 15 minutes.
...
Once I know the thrust, I can closely approximate how either engine will push my cat against the wind of various strengths, which is where I want to get to. I'm sure Mr. Cwjohm would concur with that.
In order to determine thrust at any specific boat speed and prop RPM, in addition to torque we need to know the efficiency of the prop at those values. And that is likely to vary by a factor of over x2 under various conditions.

The prop efficiency at a given boat speed and prop RPM is a function of the Velocity of Advance (i.e. the speed of the water flow immediately in front of the prop. This is is some percentage of boat speed and depends on the hull profile, siting of the prop etc.) and diameter, pitch, slip, blade cross section area and blade profile of the prop in question.

IOW, you can't generalise thrust from just input torque and RPM, it varies tremendously with boat speed and prop design, (Hence my comment about a 45HP engine only generating 1205 prop RPM must be driving a large, coarse prop)

If you assume the same boat and saildrive configuration and the same prop, then all of those cancel out and the only variable that matters is power delivered to the prop and that is HP or kW.


And forget about that bollard pull. That is by definition at 100% slip and you will never experience that with a moving boat under any conditions.
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Old 06-12-2016, 04:05   #574
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Once I know the thrust, I can closely approximate how either engine will push my cat against the wind of various strengths, which is where I want to get to. I'm sure Mr. Cwjohm would concur with that.
At low speed it is true that 15kW of electric is about the same thrust as 45kW of diesel because a cruising boat has no variable gear reduction. But thrust changes as soon as the boat starts moving through the water. I think your fixation on thrust and torque are blinding you to a simpler way of thinking. It takes energy to move a boat through the water. For a given hull and displacement it takes the same amount of energy to move the boat from point A to point B no matter where that energy comes from. Power is just the amount of energy expended per unit of time. So total energy is the average power multiplied by the total trip time. There is absolutely no way 15kW can be "about the same as 45kW" once your boat is moving at any reasonable speed. It's just hype to claim that. It takes horsepower to overcome wind and waves because these things require energy from the boat to overcome. Energy divided by time is power. Therefore it takes a certain amount of power to achieve a desired trip time regardless of thrust or torque. Thrust and torque are just the variables we tweak to achieve maximum efficiency, they are not the same as power and energy.
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Old 06-12-2016, 04:11   #575
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Re: Oceanvolt Hybrid Motor

So the claim you are presenting is the 15kw ocean volt motor puts out 290Nm at 2200RPM.


That's really odd because that calculates out to around 90hp or 75kw. I'm really shocked that they would under-rate their motors by a factor of 5!


That really is some magic HP if you can input 15kw of electricity and get 75kw of mechanical power out.
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Old 06-12-2016, 14:38   #576
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post


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.
15 kW = 15000 Watts
2200 RPM = 2200/60 RPS = 36.667 RPS = 36.667*2*pi radians/second = 230.383 radians/second
15000 W / 230.383 radians/second = 65.109 Nm
Therefore OV SD15 produces 65.1 Nm at rotorshaft at 2200 RPM.
SD - ELECTRIC SAIL DRIVE MOTORS
That link states that it has a gear ratio of 1.93:1
Therefore it would have 65.109 Nm*1.93 = 125.66 Nm at the prop shaft if the gear where 100% efficient. It isn't, therefore it's more like 120 Nm or a little more, but that much we can be sure of. And the propshaft has 1140 RPM while the rotor has 2200 RPM at the same time, due to gear ratio.

I don't know from where you got it's torque at zero RPM, but it can definitely be much more than 120 Nm at propshaft.

I conclude your numbers were neither magic nor physics, they were just wrong.
And if the prop in question does have those 1140RPM with OV SD15, it is too small for the diesel with 2.49:1 reduction gear. If it's instead matched with the diesel, OV SD15 will not be able to rotate at full revs with that prop, but can still most likely produce the same power at less revs and more torque. But the prop will produce then less thrust with SD15 as it is rotating slower than with diesel.
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Old 06-12-2016, 14:50   #577
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
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.
Sorry, but no locking involved in Toyota prius.
The Power Split Device - How Hybrid Cars Work | HowStuffWorks
" Once you are up to freeway speed, the car will move under a combination of gas and electric power, with all of the electricity coming from the generator."

Search for "prius PSD" to find more sources for the same effect.
Prius doesn't have traditional gear box to match car speed and engine RPM. If relies on PSD to function as a variable transmission by the generator RPM to be whatever is needed.
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Old 06-12-2016, 15:01   #578
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
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?
190 NM at 1140 RPM = 22 682 Watts. SD15 is not capable of producing that much power continuously, only 15 000 Watts. (ps, I'm not sure it could produce over 22 kW even instantaneously)
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Old 06-12-2016, 15:27   #579
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Re: Oceanvolt Hybrid Motor

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Sorry, but no locking involved in Toyota prius.

I don't have Prius. Most others (e.g. Honda) use CV transmissions and the engine drives the wheels directly. The electric motor provides starting torque and braking. I suspect Toyota wishes they had done that too.
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Old 06-12-2016, 17:38   #580
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Re: Oceanvolt Hybrid Motor

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I don't have Prius. Most others (e.g. Honda) use CV transmissions and the engine drives the wheels directly. The electric motor provides starting torque and braking. I suspect Toyota wishes they had done that too.
You wrote Toyota and I responded to that.
And no, they don't wish they had done it otherwise. Their system allows optimizing load on the engine and that results far greater increases on ICE efficiency than the increased efficiency losses due to partially electrical transmission instead of gears. Their system has proved to be more efficient by independent testing of hybrid cars up to 100 km/h speeds. And most driving in most countries is below that speed most of the time.
They are not claiming the same benefits on efficiency applies at max speed on German motorways.
Had they not patented their system some other manufacturers would have copied their system.
Toyotas system does however cost more to buy, and most likely to manufacture too.
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Old 06-12-2016, 21:38   #581
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Re: Oceanvolt Hybrid Motor

Create energy while sailing


It's interesting to see oceanvolts regeneration numbers (see graph in link).


Yeah, it can put out 3000-3500w...but that's when you are doing around 17kts.


At a more reasonable but still optimistic for long duration 7kt speed it appears to be down around 200-250w of about the same as a solar panel.


The graph doesn't even show output at much more reasonable 4-6kt cruising speeds which typical cruising boats do on long voyages but it's safe to say, it tails off drastically.
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Old 08-12-2016, 16:59   #582
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
Create energy while sailing


It's interesting to see oceanvolts regeneration numbers (see graph in link).


Yeah, it can put out 3000-3500w...but that's when you are doing around 17kts.


At a more reasonable but still optimistic for long duration 7kt speed it appears to be down around 200-250w of about the same as a solar panel.


The graph doesn't even show output at much more reasonable 4-6kt cruising speeds which typical cruising boats do on long voyages but it's safe to say, it tails off drastically.
It tails off quite drastically for ANY hydro generator, that's just the way it goes. Better for cats, not so much for mono's...bad luck. But for many cruising cats on a reach or even on downwind crossings, there can be alot of power generated i.e in around a kilowatt or more. If you have LFP, they suck that up and recharge pretty quickly. For a typical 400Ah house bank, that's a full recharge in about 5 hours while doing 8 to 9 knots. I'd be pretty happy with that.

And things will be getting even better in the not too distant future.
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Old 08-12-2016, 17:43   #583
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Re: Oceanvolt Hybrid Motor

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For a typical 400Ah house bank, that's a full recharge in about 5 hours while doing 8 to 9 knots. I'd be pretty happy with that.
Yeah, most folks would be ecstatic... but if you look at some of the cruising cat speeds that Pollux has posted for the current ARC, you will see that even without the drag of the turbine, those speeds are not realistic expectations for most boats, no matter what the number of hulls.

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Old 08-12-2016, 18:33   #584
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Re: Oceanvolt Hybrid Motor

What could possibly go wrong with all that state of the art electrickery floating around?

News - Fire aboard Conrad Colman’s boat - Vendée Globe 2016-2017
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Old 08-12-2016, 18:40   #585
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Re: Oceanvolt Hybrid Motor

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It tails off quite drastically for ANY hydro generator, that's just the way it goes. Better for cats, not so much for mono's...bad luck. But for many cruising cats on a reach or even on downwind crossings, there can be alot of power generated i.e in around a kilowatt or more. If you have LFP, they suck that up and recharge pretty quickly. For a typical 400Ah house bank, that's a full recharge in about 5 hours while doing 8 to 9 knots. I'd be pretty happy with that.

And things will be getting even better in the not too distant future.
I notice they are careful not to include grid lines but it looks to me like 1000w output is up around 10kt cruise speed. At 8kts, it's definitely well below 1000w output but again, these are the subtle marketing methods used to oversell the product.

There are cats that can do that in good conditions but the vast majority of cruising boats (cat or mono) will never see sustained speeds in that range.

Even if you have a boat that can manage those speeds in near perfect conditions...how many days per year can you expect to be running offshore per year? Much simpler and more reliable to fill that 400Ah battery bank with solar because it won't care if you are racing at double digit speeds or not.

Of course this is still just a side issue. I'm still waiting to hear how a 15kw motor is generating 75kw of power at the prop. If you can answer this with a reasonable answer that can be explained by physics, I'll agree with anything else you claim about Ocean Volt.
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