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Old 10-12-2018, 12:52   #1471
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
From that page you can download the engine manuals.
The 3YM20 is not the same engine as the 3YM30AE. And the actual continuous rating can be found on the plaque according to the manual last I looked. You're looking at the break-in procedure perhaps?

Yanmar says (https://www.yanmar.com/global/suppor...leasure.html):

Quote:
Max output less than 5% of total operation hour, continuous operation duration (full throttle) less than 30min
Standard operation; less than 90% of the maximum engine speed
Even if you take 3,200RPM as a given then (about 89%), you're well outside of the efficiency curve. Compared to 2,400RPM you're burning twice the fuel to get about 25% more power.

Seems like a pretty silly argument to me.
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Old 10-12-2018, 13:01   #1472
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Re: Oceanvolt Hybrid Motor

Even if you have 30HP continuous duty electric drives where do you get the 40kW of power needed to feed them electricity? Answer: An 80HP diesel using a 50% longevity factor.

And there is no point in comparing continuous duty electric unless you can actually run extended periods (days) at full power. No electric boat can do that without ICE driving a generator. Most canít even run 24 hours on batteries let along a week.

No ICE->generator->inverter->induction motor->propeller system will be more efficient on a liters per mile basis that a plain old ICE->gear->propeller if both are properly designed to same specifications. A cruising ICE and gear train is running at pretty much the optimum point for efficiency and longevity. EP cannot change that.
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Old 10-12-2018, 13:19   #1473
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by ssmoot View Post
The 3YM20 is not the same engine as the 3YM30AE. And the actual continuous rating can be found on the plaque according to the manual last I looked. You're looking at the break-in procedure perhaps?

Yanmar says (https://www.yanmar.com/global/suppor...leasure.html):



Even if you take 3,200RPM as a given then (about 89%), you're well outside of the efficiency curve. Compared to 2,400RPM you're burning twice the fuel to get about 25% more power.

Seems like a pretty silly argument to me.
The manual covers a rsnge of engines.

The specifications are on pages 82 to 84.

In every case, continuous power output is far more than 50% of rated maximum.

So the claims that in order to have 15 kW available continuously you'd need to buy 30 kW motors appear to be unsupported.
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Old 10-12-2018, 13:26   #1474
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Re: Oceanvolt Hybrid Motor

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Even if you have 30HP continuous duty electric drives where do you get the 40kW of power needed to feed them electricity? Answer: An 80HP diesel using a 50% longevity factor.
Answer: Not from a diesel running at 89% of redline.

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Originally Posted by transmitterdan View Post
No ICE->generator->inverter->induction motor->propeller system will be more efficient on a liters per mile basis that a plain old ICE->gear->propeller if both are properly designed to same specifications.
So let's nail this down with real numbers. Your inverter/charger is better than 90% efficient. Your motors are better than 90% efficient. Generators vary, but I seriously doubt a ~2L 1800RPM generator selected with efficiency in mind is as inefficient as a much smaller diesel at 3200RPM.

The diesel doesn't doesn't make power from the sun or regeneration. Which if you manage to squeeze 3kW of solar on your boat like others on the forum might actually make you consider ditching the diesel generator all together and instead carry a pair of gas generators.

You aren't going to cruise for days with that setup, but it has other advantages of course. You can buy a lot of battery capacity for the factory price of a diesel generator.

Quote:
Originally Posted by transmitterdan View Post
A cruising ICE and gear train is running at pretty much the optimum point for efficiency and longevity.
Not a small Yanmar running at 3,200.

I don't think you're necessarily making that argument, but hopefully you can appreciate the difficultly of trying to discuss an issue when different people are talking about different goalposts.
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Old 10-12-2018, 13:29   #1475
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
So the claims that in order to have 15 kW available continuously you'd need to buy 30 kW motors appear to be unsupported.
So if you decided you needed 15kW to cruise comfortably, you'd buy 15kW diesels?

Of course you wouldn't. That's entirely disingenuous.

That's the point of the argument. You can't cruise continuously, safely, and efficiently by sizing a diesel's max output to your cruising requirements. Period.

The same is not true for EP.
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Old 10-12-2018, 13:38   #1476
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
So if you decided you needed 15kW to cruise comfortably, you'd buy 15kW diesels?

Of course you wouldn't. That's entirely disingenuous.

That's the point of the argument. You can't cruise continuously, safely, and efficiently by sizing a diesel's max output to your cruising requirements. Period.

The same is not true for EP.
Speaking of entirely disingenuous.....

No, if you needed 15kW, the continuous rating is less than 15kW. Its 13.9kW remember?

But its not 7.5kW as has been claimed.

So you'd size according to the continuous rated output.
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Old 10-12-2018, 13:54   #1477
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Re: Oceanvolt Hybrid Motor

BTW, no one is avoiding the fact that just because electric HP magic is real, that we still need to carry a big ICE to go long distances. That is still true until solar panels become way more efficient, or batteries store way more energy or...

However, a strong case can be made for that big engine being so much more efficient as a generator at a designed steady state speed, that it makes up for all losses in electric conversion.

PS: I'd skip the inverter and use a DC generator. Puts little/no load on the batteries when close to power needed at desired cruising speed and removes a source of inefficiency.
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Old 10-12-2018, 14:05   #1478
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
So you'd size according to the continuous rated output.
Agree with this point, just seems the mfg's are all over the place with this. I am stuck on Yanmar's inconsistency in rating. They contradict themselves.

You also picked a specific engine. Even if this particular engine's continuous is close to it's maximum without any conditions/exceptions (my instincts tell me to doubt it), it's not true for most ICE's.
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Old 10-12-2018, 14:27   #1479
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
Speaking of entirely disingenuous.....
Is that foreshadowing about the comment you're about to make?

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Originally Posted by 44'cruisingcat View Post
No, if you needed 15kW, the continuous rating is less than 15kW. Its 13.9kW remember?

So you'd size according to the continuous rated output.
Guess so.

No, you wouldn't size for the continuous rated output. Or at least I wouldn't. The idea of burning twice the fuel to achieve cruising speed seems ridiculous to me. There's no way you're burning 100 gallons/year or whatever you've claimed while keeping that as your benchmark. You've either overspecced your diesels to run efficiently and you don't actually need 15kW (or 13.9kW), or you basically never use 'em.

Can we not just have an honest conversation and say you shouldn't be buying 15kW diesels if you want 15kW of cruising power, but you can do exactly that with EP and that's ok?

I really don't understand why this is so hard to understand.
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Old 10-12-2018, 14:27   #1480
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Re: Oceanvolt Hybrid Motor

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You can't cruise continuously, safely, and efficiently by sizing a diesel's max output to your cruising requirements. Period.

The same is not true for EP.
I'm curious about the power reserve that might be included in "cruising requirements."

When sizing a diesel for hull-speed cruising, the duty cycle limitations force you to make use of only a fraction of the engine's rated power for continuous duty- you HAVE to...allowing the engine to survive. Also, for efficiency, you WANT to run it under this limit anyway...to save fuel. Fair enough- you buy a diesel that cannot even use it's max prop HP for more than a few minutes, so the rated HP number must be higher than what you need for constant motoring. Two times? Ok. Now you've got a few minutes of WOT max power sitting there just waiting to be used short term. No, you won't get all the rated power to the prop but you will get MORE power. 15%? 25%? I can think of a lot of reasons to wish for another 15% for a short period of time, some of which might even be in reverse.

When sizing a typical electric motor for hull-speed cruising, how much power reserve is there? (Not much from some of the math I have seen.)
Is considerable short-term power reserve part of cruising safely?
Maybe not, but IMO it seems a bit disingenuous to tout the 2:1 diesel:electric HP rule of thumb without mention of WOT reserve-power differences.
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Old 10-12-2018, 14:45   #1481
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Re: Oceanvolt Hybrid Motor

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Maybe not, but IMO it seems a bit disingenuous to tout the 2:1 diesel:electric HP rule of thumb without mention of WOT reserve-power differences.
If you need that 25% extra power, you should probably build it into your EP design. I don't know if Oceanvolt's system lets you overpower. That would make apple to apple comparisons a lot easier.

Some EP systems do allow you to throttle up to peak (vs nominal) power though. If that power margin is important to you, then you might want to look at those.

Or look at larger motors. But then you've got the continuous debate all over again since the diesel won't have the stamina or efficiency of the electric.

You can slice this pie any way you want to say whatever you want. But what's practical and what's realistic?

It's realistic to have a really big battery bank, lots of solar, electric motors and only portable generation I think.

Or a large diesel generator sized for max propulsion demands, as small a battery bank as your current demands allow for, and electric motors.

Or a diesel generator sized for fractional requirements (say 5kW), a 1C battery bank, and electric motors.

Or twin diesel direct drives.

They're all valid options.

What's not valid is claiming that the peak HP rating of a diesel is the most important number for everyone. I don't think I've ever seen an engine sizing discussion here come to that consensus, but that rationale seems to dominate this thread. It's silly.
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Old 10-12-2018, 15:00   #1482
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Re: Oceanvolt Hybrid Motor

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I'm confused by your post, I'm not sure what part of my math you are questioning.

Edits (sorry, way too many as I worked to understand you and Yanmar).

My source for pleasure duty: https://www.yanmar.com/global/suppor...epleasure.html

Maybe Yanmar rates pleasure duty differently than most? Everything is possible.

I do see the engine you reference, which lists continuous power, but they still rate it as pleasure duty, on the page I linked above with the asterisks/definitions they put at bottom. I'm not a Yanmar expert, but I have worked with duty ratings before. Pleasure duty is very light use and does not match the numbers you are showing. Their documentation is contradictory, but I can't debate their words, only they know. Duty rating is still an input no matter what single data point you find. Maybe there's some honest engine manufacturers, maybe there's some dishonest electric motor manufacturers, I wouldn't be surprised by either.

My 3 cyl Yanmar max rating (1 hour) is 20.1KW, continuous is 17.7KW (88% of max KW). I cruise at an rpm that CAN produce 15KW (2800rpm) due to best fuel/torque efficiency. You must realize my engine CAN produce 15KW at 2800rpm, but will only produce whats needed to maintain 2800rpm with the given load, i.e., if the load only requires 12KW, the governor will adjust the fuel input accordingly. Without precise fuel measurement, we don't know the power required to cruise.


So, yes, it is very likely that a 12KW EP will push my boat at cruise speed in normal (semi-benign) conditions. But it certainly won't do the job in conditions that require 17.7KW to push my boat at cruise speed. IMO, building a system with zero reserve power is foolish.


Plus, if you have to run ICE to produce the power for EP, I contend you are less efficient that ICE direct drive. For certain, you carry more weight as you must size the ICE to cover the losses in the system.


Then you have to look at cost differences.
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Old 10-12-2018, 15:19   #1483
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Re: Oceanvolt Hybrid Motor

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For certain, you carry more weight as you must size the ICE to cover the losses in the system.
That's not a given. Two 10kW generators will weigh significantly more than a single 20kW generator for example.

In my spreadsheets the worst I can manage is an EP design that weighs about the same as a typical three-diesel plus Lead Acid design. But it's not too difficult to come up with a system a couple hundred kilograms lighter as well.

It all depends on what trade-offs are important to you. Weight and cost are my biggest ones.

You're not wrong about price of course. Batteries can be relatively cheap, but it's hard to get around the fact that EP motors/saildrives tend to cost every bit as much as diesels with sail drives. That makes a repower a pretty expensive proposition.

ElectricYacht's 20kW saildrives are $13,495 each for example. Which is maybe great for some, but too much for me.
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Old 10-12-2018, 15:21   #1484
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Re: Oceanvolt Hybrid Motor

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Agree with this point, just seems the mfg's are all over the place with this. I am stuck on Yanmar's inconsistency in rating. They contradict themselves.

You also picked a specific engine. Even if this particular engine's continuous is close to it's maximum without any conditions/exceptions (my instincts tell me to doubt it), it's not true for most ICE's.
It was true for all the engines I looked at. Frankly I couldn't be bothered searching for examples where it wasnt.
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Old 10-12-2018, 15:28   #1485
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
If you need that 25% extra power, you should probably build it into your EP design. .
But, but..... then your 2:1 or 3:1 or 5:1 power equivalence goes out the window!

And while the electric faithful keep carping on about the continuous power capabilities of diesels, they seem to ignore the fact that most electric installations size a generator that doesnt come close to allowing continuous 100% throttle on the electric motors.
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