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Old 16-11-2016, 07:34   #301
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
Actually, a typical cruising boat will have no need for changing gears. Gear changing is only needed when you need a vehicle to operate over a wide range of speeds and thus the engine cannot stay in it's ideal RPM range without multiple gears.

For a cruising boat, it only needs to be set up for optimum operation of the diesel at cruising speed which most production models do a pretty good job at because it's an easy change for the manufacturer to spec the ideal prop and that costs nothing and provides better performance. (You do hear of one-off or repowered boats having issues or boats with significant bottom growth but not really relevant to the discussion as it's usually the result of a poor.)

Starting from a standstill it's less efficient but since the prop slips in the water, it's not an issue and so unless you are running a short distance ferry that starts and stops constantly, the diesel drivetrain is pretty much at it's peak efficiency.

Keep in mind, it's not only the transmission that determines the ideal loading on the engine. The pitch of the prop effectively is part of the gearing. So if you originally thought you needed a 2.3 gear ratio and the closest available is a 2.4 gear ratio, you just adjust the pitch slightly and you wind up with effectively the same load on the engine and you stay in that nice efficient RPM range for the diesel.
You can do that, but then the engine doesn't rev up at WOT.
The prop would require more power than is available at recommended rev range for WOT. Using WOT with such heavy prop leads short engine life.
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Old 16-11-2016, 07:51   #302
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Re: Oceanvolt Hybrid Motor

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Yeah, tons of cruising boats have sail drive legs that rotate 180 degrees...

In the real world we have propellers that are designed to turn out best efficiency at something like 500-1000 shaft RPM producing 5-10 knots. No cruising boat can drag that same propeller through the water and get even a tiny fraction of 500RPM from the prop while producing significant power. The design of the propeller is all wrong for that application. A propeller designed to transmit 25HP to the water at 1000RPM can't produce even 1/10 of that power as a water turbine traveling through the water at 5-10 knots so they are pretty inefficient as power generators.
Most cruising boats don't have electric drives, therefore no driveleg rotation.
Any electric drive intended to be used as a turbine are worth nothing if they don't rotate. It at the very least doubles the efficiency as a turbine, possibly more depending on prop dimensions. 40% turbine efficiency for a prop is easy to achieve if working backwards.
The best revs for max efficiency for most boat props is below 500 rpm, but that is totally useless as the thrust is minimal, and engine efficiency is also minimal.
How much power a prop can produce as a turbine in a given boat speed has nothing to do with efficiency, but a lot to do with effectiveness. Totally different concepts, as the former involves the amount of drag force as well, which you ignore.
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Old 16-11-2016, 08:02   #303
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
So if we assume your numbers are correct (they are not but for the sake of argument...), diesel still has 36 times the energy density of the very expensive Li battery banks. (105 times for lead acid).

Even if you assume 75% efficiency losses (assuming an engine that is running horribly as a typical diesel does significantly better) converting diesel to mechanical energy and the batteries have 0% efficiency loss, it's still an order of magnitude more available propulsive energy.

If they ever get that ratio down into the single digits (at reasonable prices), there will be a revolution. Until then batteries simply do not store enough energy to meet the typical cruisers expectations.
With 75% efficiency losses the brake specific fuel consumption would be 330 g/kWh for the diesel engine. Why should I assume that?
And under what loading conditions?

You can't define energy losses for batteries when only motoring but not charging. Both have to be considered, which are not available when discussing energy densities. Those depend only on motor and wire&connection losses, not on batteries.
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Old 16-11-2016, 08:12   #304
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
You can do that, but then the engine doesn't rev up at WOT.
The prop would require more power than is available at recommended rev range for WOT. Using WOT with such heavy prop leads short engine life.
Umm, no.

The whole point is to match the drivetrain to the engine output at peak efficiency. By picking a reduction gear and prop pitch, you can dial it in near perfectly.
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Old 16-11-2016, 08:12   #305
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
You can do that, but then the engine doesn't rev up at WOT.
The prop would require more power than is available at recommended rev range for WOT. Using WOT with such heavy prop leads short engine life.
And in addition, it would still have low efficiency when motor-sailing in light winds, those conditions would require even higher pitch or less revs for the engine for the same prop revs, another gear ratio.
Typical useful power range is quite large for boats, 5...100% max power, and engine revs can't be changed anywhere near that much as would be necessary for optimal fuel consumption.
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Old 16-11-2016, 08:15   #306
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
With 75% efficiency losses the brake specific fuel consumption would be 330 g/kWh for the diesel engine. Why should I assume that?
And under what loading conditions?

You can't define energy losses for batteries when only motoring but not charging. Both have to be considered, which are not available when discussing energy densities. Those depend only on motor and wire&connection losses, not on batteries.
I agree 75% losses for the diesel is way overstating reality in an attempt to give your assumptions their best shot at making battery storage viable and it still falls an order of magnitude short.

Agreed, there are energy losses charging and discharging the batteries plus through the rest of the system. Again, I was giving you the benefit of the doubt and it still falls an order of magnitude short.

The point still stands: the biggest limitation to the adoption of electric drivetrains is the energy density of the storage system.
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Old 16-11-2016, 08:16   #307
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
Umm, no.

The whole point is to match the drivetrain to the engine output at peak efficiency. By picking a reduction gear and prop pitch, you can dial it in near perfectly.
Yes, either peak efficiency in one operating speed and loading (possible windage, seaway or saildrive) or max power, not both at the same time.
For max efficiency engine torque should not change more than a factor of 2 in either way in available rev range.
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Old 16-11-2016, 08:21   #308
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Re: Oceanvolt Hybrid Motor

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I agree 75% losses for the diesel is way overstating reality in an attempt to give your assumptions their best shot at making battery storage viable and it still falls an order of magnitude short.

Agreed, there are energy losses charging and discharging the batteries plus through the rest of the system. Again, I was giving you the benefit of the doubt and it still falls an order of magnitude short.

The point still stands: the biggest limitation to the adoption of electric drivetrains is the energy density of the storage system.
Your last conclusion is valid for full electric systems, not hybrid with electric drivetrains.
What made you assume that I claimed battery storage would be viable?
Nothing to do with electric drive being viable.
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Old 16-11-2016, 08:22   #309
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Re: Oceanvolt Hybrid Motor

Why do people keep comparing diesel fuel potential energy to battery energy storage pontential???? This is not relevant, nor the limiting factor on a HYBRID system. We're talking hybrids here people!!!
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Old 16-11-2016, 08:28   #310
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Just Another Sa View Post
And in addition, it would still have low efficiency when motor-sailing in light winds, those conditions would require even higher pitch or less revs for the engine for the same prop revs, another gear ratio.
Typical useful power range is quite large for boats, 5...100% max power, and engine revs can't be changed anywhere near that much as would be necessary for optimal fuel consumption.
Motorsailing is already massively more efficient than straight motoring, so the marginal improvement in MPG isn't a big deal. Even at low RPM, diesels don't lose that much efficiency. Certainly not enough to justify the cost of conversion and lack of performance in more demanding conditions.

As has been mentioned numerous times, we aren't talking about new technology or new ideas. They've been tried for decades (really even back to the 1800's) and haven't unseated diesel as the power plant of choice.
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Old 16-11-2016, 08:29   #311
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Re: Oceanvolt Hybrid Motor

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Why do people keep comparing diesel fuel potential energy to battery energy storage pontential???? This is not relevant, nor the limiting factor on a HYBRID system. We're talking hybrids here people!!!
If you want to limit it to hybrids, then it's all just silly as you have all the negative aspects of a diesel power train plus the negative aspects of an electric drivetrain with the one exception that the battery storage isn't the limitation.
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Old 16-11-2016, 08:38   #312
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Re: Oceanvolt Hybrid Motor

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Your last conclusion is valid for full electric systems, not hybrid with electric drivetrains.
What made you assume that I claimed battery storage would be viable?
Nothing to do with electric drive being viable.
Who said an electric drive leg wasn't viable? It's just silly to substantially reduce the overall drivetrain efficiency by introducing a hybrid system.

If you are running the generator anyway, out goes any motorsailing advantages.
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Old 16-11-2016, 08:40   #313
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Re: Oceanvolt Hybrid Motor

All the advocacy reminds me of the numerous garage startups that tried to market hybrid cars or EVs before Toyota made the Prius and Tesla/Nissan introduced the Model S or Leaf.

Spend all day talking about the efficiency of the motor, present range based on unrealistic driving/AC usage condition and cherry pick performance figure from 0-25mph.

Real consumers that aren't evangelicals sort through the BS by three simple questions:

1. What will it cost me? Install/maintain/energy cost/future life expectancy? Itll cost more to install, limit my cruising to costal with marina power, battery degrades by 4% per year without considering deep cycle. Nope.

2. How will I recharge? What's my range at normal hull speed? (No I won't sail at 4 knots for 72 hours). 6 nm at full power. Nope.

3. What's the performance benefit? Weight you lug around whether you have energy potential or not. No better real life cruisingperformance . Nope.

End of story.

Im not anti EV. Appreciate what the Prius has done, wouldn't rule out owning a Model 3 or something like it - but I don't have a garage at sea, can't call AAA to tow me home, or call a cab. If one loses a mast, diesel offers you margin of safety. Fuel can be transferred. Batteries cannot. End of story.

Electric boats will more likely when batteries get better and are a better natural fit for powerboats, smaller dailsail/racing boat outboards where range anxiety, function and purpose and fuelaavailability limits your cruising ground anyway.
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Old 16-11-2016, 09:56   #314
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
If you want to limit it to hybrids, then it's all just silly as you have all the negative aspects of a diesel power train plus the negative aspects of an electric drivetrain with the one exception that the battery storage isn't the limitation.
Excellent reason for opposing any and all innovation. We get it: you are an old and highly experienced sailer, and like most elderly, highly resistant to change, even if said change doesn't directly effect you in any way. Many have and will fail to refine cruising propulsion systems, but if history has taught us anything about technology, it's that eventually enough money, genius, and creativity will make it's way into this issue to come together to form an improved system despite the resistent drunken old sailors, who yell and throw empty bottles of rum at the innovators while wrenching away on their rusty old diesels that have lasted for 30 years.
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Old 16-11-2016, 10:02   #315
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Re: Oceanvolt Hybrid Motor

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Originally Posted by valhalla360 View Post
If you are running the generator anyway, out goes any motorsailing advantages.
No, the best thing about hybrids is better efficiency during motorsailing compared to traditional diesel drive due to optimising revs of prop&engine.
20% more range at a given speed is achievable.

Another advantage of electric drive comes with rotating drive leg if available (Gunboat 60 Moonwave have one), no need for bow or stern thrusters and better and easier control than with them while docking. And as a bonus the prop charging as a turbine.
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