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Old 30-11-2019, 18:42   #1936
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cj88 View Post
I see this comparison between hp and watts but what it sounds like from those that have gone electric say about the performance makes me wonder if there should also be more of a comparison of torque at different rpm when trying to compare performance on the water between a given ICE and an electric motor.

Of course the EP proponents keep talking about torque and ignoring HP, because EP has high torque at very low RPM, unlike a diesel.


But its HP at the prop that drives a boat, not torque.
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Old 30-11-2019, 19:22   #1937
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Re: Oceanvolt Hybrid Motor

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Thanks for that but perhaps I wasn't being very clear. I know that there is a direct relationships between hp and watts and I know that there is a direct relationship between torque and power. I never suggested otherwise and I never mentioned any "magic electric horsepower". What I was trying to suggest is that there should be more consideration given to the different torque characteristics at different rpm of an ICE and an electric motor in a given use case scenario to help people understand how a boat may perform with the different options as just looking at a max hp or a max kW figure doesn't tell the whole story.



Very high torque at very low RPM is great if you are driving one of these:





Not so much value on a sailboat's auxillary drive.
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Old 30-11-2019, 20:12   #1938
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cj88 View Post
Thanks for that but perhaps I wasn't being very clear. I know that there is a direct relationships between hp and watts and I know that there is a direct relationship between torque and power. I never suggested otherwise and I never mentioned any "magic electric horsepower". What I was trying to suggest is that there should be more consideration given to the different torque characteristics at different rpm of an ICE and an electric motor in a given use case scenario to help people understand how a boat may perform with the different options as just looking at a max hp or a max kW figure doesn't tell the whole story.

As I wrote, the only difference is torque at what RPM and the chance of swinging a larger, slower, amd hence more efficient prop.


Torque is not work; its just force. Horsepower (or watts) is the measure of work done, and a horsepower is a horsepower whether it comes from electricity or infernal combustion, or indeed - a horse.
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Old 30-11-2019, 20:13   #1939
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Re: Oceanvolt Hybrid Motor

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Originally Posted by StuM View Post
Very high torque at very low RPM is great if you are driving one of these:





Not so much value on a sailboat's auxillary drive.

Indeed. What a beauty!
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Old 30-11-2019, 23:52   #1940
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Re: Oceanvolt Hybrid Motor

If you have a chance, try an electric car.
The difference to an ICE one is obvious.
And even my little Zoe goes like stink, even with only 88HP. So I think, that is comparable with boats.
And manufaturers of electric boat propulsion need to compare to something and that is the diesel or outboard.

What I would like even more is the silence that comes with electrification. Listening to a diesel engine right beside my head is not very pleasant over a longer time.
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Old 30-11-2019, 23:56   #1941
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Re: Oceanvolt Hybrid Motor

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I see this comparison between hp and watts but what it sounds like from those that have gone electric say about the performance makes me wonder if there should also be more of a comparison of torque at different rpm when trying to compare performance on the water between a given ICE and an electric motor.
Ummm...that is exactly what is done.

HP = torque * RPM.

Opps already addressed.

For cars in city driving, that low end torque (and resulting low end HP) make a big difference. You can use a significantly smaller motor to achieve similar performance in a car because in city driving, every minute or two you are going from 0 mph to 35-45mph and back to 0 mph. Low speed acceleration makes a big difference in what people perceive as performance.

With a displacement cruising boat, the typical operation is to go for 0 mph to 6 mph and then leave it there until you reach your destination...At a steady cruising speed, assuming the same prop, HP is HP...there is no magic HP.

As far as turning a really big low pitch prop...sure but you can do that with a reduction gear on a diesel for the same effect (gears can multiply torque)...it's not done because no one cares much about acceleration on displacement cruising boat but if you find it important, it's not hard to achieve and the power source is largely irrelevant within normal ranges.
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Old 01-12-2019, 00:06   #1942
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Re: Oceanvolt Hybrid Motor

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What I would like even more is the silence that comes with electrification. Listening to a diesel engine right beside my head is not very pleasant over a longer time.
Has your muffler failed? I've accidentally tried to restart my motor when a bridge opens because I though it stalled. I've been on numerous boats where unless you firewall the throttle, they don't make much of any noise.

Yeah, when I had a twin V8 power boat it was noisy but also impractical for electric power (energy storage not electric motors).
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Old 01-12-2019, 00:31   #1943
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Re: Oceanvolt Hybrid Motor

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Magic electric HP again?
The point is that these very small gasoline outboard are horribly bad (in terms of real thurst in the water, prop efficiency etc.). If you have ever tried them im comparison with a good, well optimized electric outboard you would understand this.

But my statement was about if 1 knot can be achieved from solar when crossing the doldrums. For this you may want to look at hull resistance curves and just compare numbers.
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Old 01-12-2019, 00:34   #1944
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Re: Oceanvolt Hybrid Motor

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The point is that these very small gasoline outboard are horribly bad (in terms of real thurst in the water, prop efficiency etc.). If you have ever tried them im comparison with a good, well optimized electric outboard you would understand this.
Give us factual evidence to support this statement (not magic HP) for use on a large cruising boat.
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Old 01-12-2019, 00:53   #1945
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Re: Oceanvolt Hybrid Motor

Starts with not having to rev it.
Full torque at 1/u min. And that allone makes a huge difference.
Power aka HP comes with revs, so if there is no need to rev the engine, you get the same result with less power.
And since there is no gear box needed there is less loss, so more power ends up on the prop.
That is why you can achieve the same with less HP.
But in order to compare it to what people know, there come the magical HP you are refering to.
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Old 01-12-2019, 01:02   #1946
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Re: Oceanvolt Hybrid Motor

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Starts with not having to rev it.
Full torque at 1/u min. And that allone makes a huge difference.
Power aka HP comes with revs, so if there is no need to rev the engine, you get the same result with less power.
And since there is no gear box needed there is less loss, so more power ends up on the prop.
That is why you can achieve the same with less HP.
But in order to compare it to what people know, there come the magical HP you are refering to.
Cruising boat...starting isn't an issue to begin with. No one is doing 0 to 6mph races with cruising boats.
Likewise max torque from 0 rpm offers no real advantage (note: power is torque x rpm, so it's not same result with less power)
Outboard HP is measured at the prop...so gearbox losses are already included when you provide the outboard HP.
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Old 01-12-2019, 01:58   #1947
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Re: Oceanvolt Hybrid Motor

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Originally Posted by harlem24 View Post
If you have a chance, try an electric car.
The difference to an ICE one is obvious.
And even my little Zoe goes like stink, even with only 88HP. So I think, that is comparable with boats.
And manufaturers of electric boat propulsion need to compare to something and that is the diesel or outboard.

I use and love electric cars (BMW i3's from my car sharing service). The acceleration in city driving is fantastic. But that is not much applicable to boats. I've heard people with Ocean Volt systems say that this low speed torque does indeed improve low speed manuevering, but as Valhalla or whoever said, once you're up to cruising speed, this does not matter at all, and that's what you're doing 99% of the time in a cruising boat.


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What I would like even more is the silence that comes with electrification. Listening to a diesel engine right beside my head is not very pleasant over a longer time.

I do agree with this. I rather like the sound of my Yanmar, which runs sweet and smooth (it's turbocharged). But I like the sound of silence even much better Definitely an advantage of electric. And because of the very short range of electric boats, not only is the sound very quiet, but you don't have to listen to it for very long.
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Old 01-12-2019, 02:04   #1948
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Re: Oceanvolt Hybrid Motor

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Originally Posted by harlem24 View Post
. . . Power aka HP comes with revs, so if there is no need to rev the engine, you get the same result with less power.
. . .
That is why you can achieve the same with less HP. . .

This is illogical and false. You need the same power to get the same result. The ability to do work is precisely the definition of power.





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Originally Posted by harlem24 View Post
. . .And since there is no gear box needed there is less loss, so more power ends up on the prop. . .

This is true, but is a very tiny advantage. Power lost in typical marine gear is only 2% or 3%.




Bottom line: If you want the "same result", you need the same horsepower, give or take 2% or 3%. Horsepower, not torque.
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Old 01-12-2019, 02:14   #1949
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Re: Oceanvolt Hybrid Motor

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I do agree with this. I rather like the sound of my Yanmar, which runs sweet and smooth (it's turbocharged). But I like the sound of silence even much better Definitely an advantage of electric. And because of the very short range of electric boats, not only is the sound very quiet, but you don't have to listen to it for very long.
Depends, if you look at, let's say the Silent Yachts, they claim that they are able to go on solar all day with 5kn on a sunny day.
They have 210kWh batteries put on the boat and two 30kW motors. To get to those 5kn they need one on half power, so you can go 14h which means that you can motor 75 nm before the need to start the genset. If the sun did not come back up again.

And on a sailboat you just need to push until the wind picks up again. And when it does, you generate your own electricity.
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Old 01-12-2019, 03:15   #1950
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Re: Oceanvolt Hybrid Motor

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The point is that these very small gasoline outboard are horribly bad (in terms of real thurst in the water, prop efficiency etc.). If you have ever tried them im comparison with a good, well optimized electric outboard you would understand this.
Torqueedo claim their 4kW outboard can match a 10hp outboard. It can't. It does in static thrust, a pretty useless metric, but once you're moving 10hp is 7.5kW, and 4kW is 4kW.

Torque at zero revs is nice for getting a wheel driven vehicle off the line. A boat's propeller at zero revs isn't doing you much good.
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