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Old 01-12-2019, 03:31   #1951
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Re: Oceanvolt Hybrid Motor

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Originally Posted by harlem24 View Post
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.
1/u min? What is that suppose to mean? Reciprocal Daltons and minutes?



Your second statement makes no sense at all. What do you mean by "result". Are you saying you get more propulsion without more power? If so, you've just invented yet another perpetual motion machine of the first kind.
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Old 01-12-2019, 03:36   #1952
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Re: Oceanvolt Hybrid Motor

Sorry, wrong language...;-)
Full torque from 1 rpm.
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Old 01-12-2019, 04:05   #1953
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Re: Oceanvolt Hybrid Motor

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Sorry, wrong language...;-)
Full torque from 1 rpm.

Yep, I'm sure a sailboat auxiliary motor with a prop turning at 1 RPM will really drive the boat at quite a speed.
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Old 01-12-2019, 04:40   #1954
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Re: Oceanvolt Hybrid Motor

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Yep, I'm sure a sailboat auxiliary motor with a prop turning at 1 RPM will really drive the boat at quite a speed.
Great reply, very funny...
But it means that an electric engine can put out more punch at lower revs.
And if you look at the Gemini thread and here, you'll see that you can go okay speed with very little power...
https://www.sailinguma.com/the-motor
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Old 01-12-2019, 04:57   #1955
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Re: Oceanvolt Hybrid Motor

One thing that's different cars vs boats:
- At 0 rpm, if you apply full torque, the car will absorb it as acceleration (up to the point where the wheels break free). Result, max torque from 0 rpm, results in snappy response from a stopped condition.
- At 0 rpm, a boat prop will start spinning before generating any significant thrust or meeting significant resistance as it slips in the water. Result, the engine can quickly spin up to an RPM where it can generate significant power.

While I'm sure someone can come up with exceptions, only time I've ever used more than 1/4 throttle docking, was tying up to a barge on the mississippi where we were fighting a 4-5kt current. Of course, snappy throttle response really wasn't an issue as we were already up to speed with the engine turning enough rpm to be in it's power band.

When you do throttle up quickly, the engine spins up to where it's generating good thrust within 1/2 sec. More often than not, extra power while docking just results in hitting the dock (or other boats) harder. Very rare for panic throttling to have a positive outcome.
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Old 01-12-2019, 05:20   #1956
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Re: Oceanvolt Hybrid Motor

The issue is that EP proponents who stand to profit from selling the tech keep talking about “equivalent HP”. And there is no such thing either in theory or practice. They need to find a better way to describe the benefit they want to promote. Using incorrect language invites the obvious criticism of “snake oil” selling. Is it really that hard to come up with a set of words or graphs that convey the benefit without inventing a new (wrong) definition of the word equivalent?

EP has many benefits but “equivalent horsepower” isn’t one of them. That is simply because a horsepower is a standard unit. The only thing equivalent to a horsepower is any other horsepower.

They could talk about energy consumption vs. boat speed for example. A nice curve showing electrical power vs. speed compared to diesel fuel consumption vs. speed would make the point. Diesel has about 9.7 kWh of potential energy per liter. So it’s possible to convert that into a graph of used potential energy as a function of boat speed. The units for diesel and EP would then be equivalent. It would show diesel power is terribly inefficient at low speed. But as already mentioned by others is that really a benefit customers care about?

This latest thread burst was prompted by the question about motoring in doldrums. The reply was that about 10 nautical miles per day could be had with solar alone as long as you don’t use any other electrical power. Is that really a benefit of EP? I would argue it is not.
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Old 01-12-2019, 05:30   #1957
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Re: Oceanvolt Hybrid Motor

Yeah, but then we are so deep in the theoretical world, most people dose off...
It seems that the way electric propulsion on a boat works, they do need less power to achieve the same result, that's why manufacturers came up with the comparison.
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Old 01-12-2019, 05:35   #1958
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Re: Oceanvolt Hybrid Motor

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Yeah, but then we are so deep in the theoretical world, most people dose off...
It seems that the way electric propulsion on a boat works, they do need less power to achieve the same result, that's why manufacturers came up with the comparison.
Still waiting for evidence that electric need less hp to achieve the same cruising speeds.
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Old 01-12-2019, 06:02   #1959
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Re: Oceanvolt Hybrid Motor

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Yeah, but then we are so deep in the theoretical world, most people dose off...
It seems that the way electric propulsion on a boat works, they do need less power to achieve the same result, that's why manufacturers came up with the comparison.

You need to go back and read the first 130 pages of this thread to see this very topic has been discussed ad nauseam.


EP proponents like to use the max rated HP of a diesel and proclaim, "that's how much HP a diesel requires to push your boat". Which is never the case....no one runs their diesel at max output to achieve cruise speed, they select an rpm for max efficiency and then match the prop to that rpm. In the end, the electric is putting out the same HP as the diesel in order to push the boat at the like speed (given the transmission loss stated earlier).
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Old 01-12-2019, 06:44   #1960
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Re: Oceanvolt Hybrid Motor

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Originally Posted by harlem24 View Post
Yeah, but then we are so deep in the theoretical world, most people dose off...
It seems that the way electric propulsion on a boat works, they do need less power to achieve the same result, that's why manufacturers came up with the comparison.

That only seems to be true if you listen to the EP vendors.


Once again, HP ( or Watts) required to drive a boat through the water at a certain speed is the same regardless of how you generate it.
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Old 01-12-2019, 06:46   #1961
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Re: Oceanvolt Hybrid Motor

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You need to go back and read the first 130 pages of this thread to see this very topic has been discussed ad nauseam.

Yep, next thing you know we will be back to comparisons with tractor pulls and sawmills
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Old 01-12-2019, 06:47   #1962
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Re: Oceanvolt Hybrid Motor

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Great reply, very funny...
But it means that an electric engine can put out more punch at lower revs.
And if you look at the Gemini thread and here, you'll see that you can go okay speed with very little power...
https://www.sailinguma.com/the-motor

Sorry, but I don't know what units you measure "punch" in. Please explain.
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Old 01-12-2019, 16:34   #1963
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Re: Oceanvolt Hybrid Motor

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I think i know the answer but, if an oceanvolt cat was out of fuel and trapped in the doldrums, could solar alone push her even at 1 knot during the day until the wind came back?
According to OV's (ha!) guesstimates to us when we asked, they say our 16tonne 50' powercat can go near 4kn on 3kW of motor power (so ignoring prop losses), or around 2kn on just over 1kW (12.3:1 LB ratio helps). On flat water, no wind of course! But that's what you're talking about in the doldrums (and let's pretend there's no ocean current either...).

If we pushed the envelope, we could probably put on 8-9kW of solar, but being conservative let's say 5kW. In the doldrums, that should get about 5x5kW or 25kWh of solar input per 24hr. If (!) we can store that amount, then in theory we could toddle along at just less than 2kn - faster than your 1 knot. The "just less" is due to battery-to-motor efficiency of around 85% at low draw so the whole 25kWh isn't available (and ignoring the battery bank size or type - as long as you're taking in what you're using AND the battery isn't totally empty at the start ).

If we solar-up the boat as we intend, at 8kW of solar in the doldrums/high sun = 5 x 8kW = 40kWh / 24h = 1.7kW available * 85% = 1.4kW to the motor which should be about 3kn (according to OV), or 72nm days. Woohoo - fastest trip out of the doldrums ever!! But, responding to the question, at least you can get out unlike the old sailing boats who were sometime stuck there for weeks, effecting the mental ability of the screw to sail when they did get wind...
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Old 01-12-2019, 18:02   #1964
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Re: Oceanvolt Hybrid Motor

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Originally Posted by mcarthur View Post
we could probably put on 8-9kW of solar, but being conservative let's say 5kW. In the doldrums, that should get about 5x5kW or 25kWh of solar input per 24hr. If (!) we can store that amount, then in theory we could
Wrong envelope.

Figure out how many usable Ah / kg you can (are willing to) buy - that determines speed/range.

At 48V, each kW of panels will deliver 65-90Ah per day (with ideal insolation) so of course you want to fit as many as possible.
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Old 01-12-2019, 19:48   #1965
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Re: Oceanvolt Hybrid Motor

9
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..........as long as you don’t use any other electrical power..
This bit always seems to be ignored. Yet the EP proponents will boast of having an "all electric galley" electric hot water etc.

These could all make quite a dent in the available motoring range.

In hot weather our fridge, freezer, watermaker, breadmaker etc have used up to 3.5 kWh per day.
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