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Old 21-12-2018, 15:45   #1786
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by bridaus View Post
Reading the Yanmar manual: 5%. This is what they'll admit to, not actual. Ratings are funny like that.

Interesting, my experience follows the Yanmar ratings.


What's been your experience?
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Old 21-12-2018, 16:04   #1787
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Re: Oceanvolt Hybrid Motor

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Originally Posted by OldMan View Post
Interesting, my experience follows the Yanmar ratings.

What's been your experience?
I'm asking for sources. You state that you have directly experienced no more than five percent loss with your transmission. Excellent, please let me know how you experienced it, I am very willing to learn and need sources to pin these numbers down.
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Old 21-12-2018, 22:14   #1788
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Re: Oceanvolt Hybrid Motor

Anyone who actually drives two same model boats at identical cruising speeds, one with diesel fueled EP and the other with mechanical will know that EP uses same or more fuel per NM. Also, a 15HP electric motor cannot drive the boat as fast as a 50HP mechanical. That’s ok and not a reason not to use EP. But for some reason the EP crowd seems offended by these simple and obvious facts. For the life of me I cannot understand why.

My transmission gets no where near 80-100C. I also feel confident that a single bearing is greater than 99% efficient. So can we agree that a very simple mechanical transmission can be 95% efficient and get on to the next bit? Like the fact that some (most?) EP systems also use gears?
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Old 21-12-2018, 23:21   #1789
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Re: Oceanvolt Hybrid Motor

Anyone who actually drives two same model boats at identical cruising speeds, one with diesel fueled EP and the other with mechanical will know that the diesel uses same or more fuel per NM. Also, a 50 HP diesel (38kW) engine will only drive the boat a knot faster than a 15kW EP even though it is over twice the size because it is so inefficient, and noisey, and maintenance intensive. That’s ok and not a reason not to use a big diesel. But for some reason the diesel crowd seems offended by these simple and obvious facts. For the life of me I cannot understand why.
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Old 22-12-2018, 00:06   #1790
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Re: Oceanvolt Hybrid Motor

I seriously despair about how strongly some people hold onto opinions in the face of contrary data. Not anecdotes, not opinions, data.
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Old 22-12-2018, 01:46   #1791
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by bridaus View Post
I'm asking for sources. You state that you have directly experienced no more than five percent loss with your transmission. Excellent, please let me know how you experienced it, I am very willing to learn and need sources to pin these numbers down.


That's a fair question. I don't know any sources on the efficiency of marine gearboxes. Here is one on the efficiency of car drive trains, including the gearboxes and axles, as measured on a dynometer:


Click image for larger version

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AUTOMOTIVE TRANSMISSION EFFICIENCY MEASUREMENT USING A CHASSIS DYNAMOMETER,A. IRIMESCU et al, Politehnica University of Timisoara, Mechanical Engineering Faculty, Timisoara 300222, Romania, 21 June 2010; Revised 17 January 2011



http://spiff.rit.edu/classes/phys216/workshops/w10c/car_engine/efficiency.pdf




Efficiency varies according to gear ratio, speed, and torque, as we might imagine.


The difference between this and a marine gearbox is the following:


A car gearbox has a layshaft, unlike a marine gearbox. So power is transmitted by two sets of helical gears. There are three shafts involved -- input, layshaft, and output, so three sets of bearings.


A marine gearbox does not have a layshaft; it has only input and output shafts, power is transmitted through one set of gears and there are two sets of bearings. Marine gearbox however may have the output shaft at an angle which is somewhat worse efficiency than when the shafts are parallel.


Someone wrote that a marine gearbox has two engagements -- not true -- you don't count the gears engaged which are not transmitting power. A car gearbox with a six speed gearbox has eight sets of gears engaged at all times (or seven if the reverse gear is not constant mesh); that does not amount to eight (or seven) engagements.


Then, a car transmission as measured on a dyno has a whole other box -- the rear axle with its own oil supply and splashing losses, another set of gears (bevel gears), and three more shafts with associated bearings, then the wheel bearings.



The car drive train with all these components measured on the dyno here is 78% to 95% efficient depending on speed of input shaft and gear ratio (what gear the gearbox is in). The lowest efficiencies come from the highest gear ratios at high input shaft speeds, which seems counterintuitive, but if you think about it -- that is from high speed of the final part of the transmission which will cause a lot of bearing friction in the rear axle and the relatively inefficient bevel gear in the rear axle.


I don't know if the car measured has IRS, but if it does, then we have 4 CV joints in the equation as well.


We don't have any of these high speed losses in the rear axle effect on a boat -- the final drive turns slower not faster than the engine. So I guess we can expect a marine transmission to be at least 3 times more efficient than a car drive train consisting of gearbox plus rear axle plus wheel bearings, and three times more efficient than the car drive train operating in the better part of the graph, so should be rather better than 95%, and maybe 97%-98%, at cruising speeds, by analogy to this measured performance.


That follows from:


Bearings: Boat 4 Car 9 (at least; if IRS then 11)
Oil sumps: Boat 1 Car 2
Gear engagements: Boat 1 Car 3





This analogy lines up well with general gear efficiency:


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http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html



And lines up with experiences in heat generated from boat gearboxes.


It would be nice to see some actual measured efficiency numbers for marine gearboxes, but the measured performance of car drive trains can give us a pretty decent idea.
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Old 22-12-2018, 05:31   #1792
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Re: Oceanvolt Hybrid Motor

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Originally Posted by tp12 View Post
I seriously despair about how strongly some people hold onto opinions in the face of contrary data. Not anecdotes, not opinions, data.


As long as people bring new supportable information, the discussion can move forward.

Our subjective brains are built to make judgement without data because back when rocks were the pinnacle of tools, and grunts were the pinnacle of knowledge transfer it's all we had to determine life or death.

We are better than that now, but we still confuse feelings with reality. This applies to both sides myself included. For the record I FEEL that EP can be more efficient, but I am FAR from knowing or proving that. I consider this discussion a journey, the outcome is not predetermined.

Dockhead's post is a great of example of contributing information to this discussion. I'm going to address it in another post.
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Old 22-12-2018, 07:18   #1793
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Dockhead View Post
That's a fair question. I don't know any sources on the efficiency of marine gearboxes. Here is one on the efficiency of car drive trains, including the gearboxes and axles, as measured on a dynometer:

Attachment 182615

AUTOMOTIVE TRANSMISSION EFFICIENCY MEASUREMENT USING A CHASSIS DYNAMOMETER,A. IRIMESCU et al, Politehnica University of Timisoara, Mechanical Engineering Faculty, Timisoara 300222, Romania, 21 June 2010; Revised 17 January 2011

http://spiff.rit.edu/classes/phys216...efficiency.pdf
This is great data. I read the study in full, it's not perfect, but it's good. It will be important to understand the differences, the methods, the stated uncertainties, and how we can apply this to marine gear.

Quote:
Originally Posted by Dockhead View Post
Efficiency varies according to gear ratio, speed, and torque, as we might imagine.

The difference between this and a marine gearbox is the following:

A car gearbox has a layshaft, unlike a marine gearbox. So power is transmitted by two sets of helical gears. There are three shafts involved -- input, layshaft, and output, so three sets of bearings.
The input and output shafts are coaxial and in our study fourth gear locks those two shafts as one (important later). There is at least one more bearing in a car manual transmission in play.



Quote:
Originally Posted by Dockhead View Post
A marine gearbox does not have a layshaft; it has only input and output shafts, power is transmitted through one set of gears and there are two sets of bearings. Marine gearbox however may have the output shaft at an angle which is somewhat worse efficiency than when the shafts are parallel.
I've been ignoring any additional complex configuration that makes the marine gear worse, because I feel EP should be compared against the typical transmissions in the application we are discussing in this thread, and some people would cry foul if we did not. We already know that in certain applications EP is considered more efficient (anything with high house loads, anything that has high variability in power needed) and DD is considered more efficient in other realms (high continuous power). It is my feeling (I admit), that if something new is to replace something that is known (DD) that it should be compared against the most typical current technology in order for folks who subscribe to current thinking to accept it. It's a judgement call, I'm open to what is "typical" in the context of this thread.

Quote:
Originally Posted by Dockhead View Post
Someone wrote that a marine gearbox has two engagements -- not true -- you don't count the gears engaged which are not transmitting power. A car gearbox with a six speed gearbox has eight sets of gears engaged at all times (or seven if the reverse gear is not constant mesh); that does not amount to eight (or seven) engagements.
That was me and you are right and I was incorrect. Those do not count as engagements for the purposes of efficiency because there is no load being transmitted.


Quote:
Originally Posted by Dockhead View Post
Then, a car transmission as measured on a dyno has a whole other box -- the rear axle with its own oil supply and splashing losses, another set of gears (bevel gears), and three more shafts with associated bearings, then the wheel bearings.
Six more bearings and one more gear (somewhat like a saildrive, but we aren't considering those here). Since the differential is not turning in dyno measurement, we should consider just the churning, the gear engagement, and the 3 shafts. The churning MIGHT be low here because the RPM at this point is fairly low at the outputs we are talking about (about 800 rpm at 60mph), but it would have to be calculated to back out it's contribution.

Quote:
Originally Posted by Dockhead View Post
The car drive train with all these components measured on the dyno here is 78% to 95% efficient depending on speed of input shaft and gear ratio (what gear the gearbox is in). The lowest efficiencies come from the highest gear ratios at high input shaft speeds, which seems counterintuitive, but if you think about it -- that is from high speed of the final part of the transmission which will cause a lot of bearing friction in the rear axle and the relatively inefficient bevel gear in the rear axle.
It is REALLY important to note here that the highest efficiency is achieved when the input shaft is locked to the output shaft in fourth gear. It's evident when you look at how much more efficient fourth gear is compared to the other gears. In other words, there is no gear engagement loss, engine direct to output shaft. Marine gear does not have this benefit, there is ALWAYS an engagement. The next highest efficiency gear is second gear at 93% at RPM's up near 4500 which is not very comparable.

The most comparable scenario here is second gear (ratio of 2.19:1) which reading the graph at 2250rpm corresponds to about 91% efficiency. Interesting.

Quote:
Originally Posted by Dockhead View Post
We don't have any of these high speed losses in the rear axle effect on a boat -- the final drive turns slower not faster than the engine. So I guess we can expect a marine transmission to be at least 3 times more efficient than a car drive train consisting of gearbox plus rear axle plus wheel bearings, and three times more efficient than the car drive train operating in the better part of the graph, so should be rather better than 95%, and maybe 97%-98%, at cruising speeds, by analogy to this measured performance.
I'm not with you here. The gear ratios in second gear in a car are very comparable. Also "I guess we can expect" and "three times more efficient" are not supported by any data.

Quote:
Originally Posted by Dockhead View Post
That follows from:

Bearings: Boat 4 Car 9 (at least; if IRS then 11)
Oil sumps: Boat 1 Car 2
Gear engagements: Boat 1 Car 3
You are missing one bearing in the boat, two in the car (let's also not count IRS, like we do not count V drive or angled output).
Gear engagements in the car are either 1 or 0 by my count and always 1 in the boat.

Quote:
Originally Posted by Dockhead View Post
This analogy lines up well with general gear efficiency:

Attachment 182616

Gears- Gear Efficiency
Ahh, one of my sources, but doesn't include bearings, churn, or load. Also, what efficiency are you assuming for the helical, 98 or 99 (if you only rely on this source)?

Quote:
Originally Posted by Dockhead View Post

And lines up with experiences in heat generated from boat gearboxes.

It would be nice to see some actual measured efficiency numbers for marine gearboxes, but the measured performance of car drive trains can give us a pretty decent idea.
I don't agree with this, "experiences in heat generated from boat gearboxes" is completely subjective. Try to get two people to agree on the temperature in a car or a shower. Their "experiences" are completely different. How about someone run at 2250 rpm for an hour and measure the ATF fluid temp, or case temp at least? Case temp will be misleading because it won't be uniform, and it will only represent the majority heat loss, but at least it would be a start. Energy can be released in many forms, work, heat (convection, radiation, conduction), and sound (probably missed one).

Our experience putting our hands on the transmission is a very imprecise AND inaccurate. To prove it, take a laser temp sensor (not that accurate, but precise enough for the task) and touch things with your hand, WRITE DOWN your guess first, and then measure with the sensor. Try not to use things you could estimate the temperature of (anything at room temperature for instance) or something fresh out of the fridge/freezer. You will find that we are terrible at temperature measurement (not even talking about heat loss, completely different!). It's just not something we need to be precise at to survive and is completely subjective. I studied this a bit a long time ago, and it was eye opening how much heat is produced and rejected by temperature differentials we don't think of as very high. I think part of the problem is that we are already 30 degrees F higher than room temperature and put out about 100 watts ourselves.

Whatever the reasons, we should not guess at heat loss, we should calculate or measure it or both. Experience is great, but we need actual measurements to get to the bottom of this.
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Old 22-12-2018, 07:55   #1794
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Re: Oceanvolt Hybrid Motor

EDIT: I take back 91% for 2nd gear at 2250rpm, it looks more like 88% based on the blue data points. Their second gear data points are all over the place, and it appears like the fitted curves might be mislabeled. The data variation is probably due to the torque generated and the ability of the equipment to measure it. They didn't report first gear due to this. Even more interesting.

PS: I have a tough time understanding how these transmissions are not putting out heat when I read things like this: https://www.foleyengines.com/tech-ti...lar-hour-gear/

Why would a reputable outfit recommend something unnecessary? And why would you cool something that isn't putting out very much heat?
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Old 22-12-2018, 09:43   #1795
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
. . . .PS: I have a tough time understanding how these transmissions are not putting out heat when I read things like this: https://www.foleyengines.com/tech-ti...lar-hour-gear/

Why would a reputable outfit recommend something unnecessary? And why would you cool something that isn't putting out very much heat?

Well, no one said they aren't putting out heat. 3% loss out of 75kW is still 2.25kW. Out of 20kW it's 600 watts. That's not nothing.


But 15% loss would be 12.5kW and 3kW respectively. I think it's an absolutely fair observation that you can feel that our gearboxes are just not putting out that kind of heat. A little box like that just can't be taking in 3kW and still be lukewarm to the touch.
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Old 22-12-2018, 10:06   #1796
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by bridaus View Post
. . .Six more bearings and one more gear (somewhat like a saildrive, but we aren't considering those here). Since the differential is not turning in dyno measurement, we should consider just the churning, the gear engagement, and the 3 shafts. The churning MIGHT be low here because the RPM at this point is fairly low at the outputs we are talking about (about 800 rpm at 60mph), but it would have to be calculated to back out it's contribution.


. . .. The gear ratios in second gear in a car are very comparable. Also "I guess we can expect" and "three times more efficient" are not supported by any data.



I agree about leaving out the differential. And I agree about second gear at 2000 RPM being the most comparable scenario. And you are right, not 3x, but anyway 2.5x -- see here:



Bearings:

Boat: Two shafts (no layshaft) with two bearings each = 4
Car: Three shafts in the gearbox = 6, plus four bearings in the rear axle of a rigid rear axle, = 3, Total 10


Churning:

Boat: one sump
Car: two sumps


Gears:
Boat: one set transmitting power
Car: three sets transmitting power -- two in the gearbox and one in the rear axle. (I'm ignoring the possibly locked input and output shafts in fourth gear; let's use the second gear data which is a similar ratio to a boat gearbox).



So I put all this into a spreadsheet with guesses as to the relative drag from each type of component:


Click image for larger version

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You can play with the relative values, but the results are always roughly similar -- boat should have about 39% of the losses of the car (so 2.56x as efficient).


So if the efficiency of the car drive train at 2000 RPM in second gear is 91%, then the boat -- ALL OTHER THINGS BEING EQUAL -- should be about 96.5% efficient. You can play with the relative significance of different components but you won't see a big variance from this.



In reality other things are not all equal, but I don't see any reason why they shouldn't be roughly equal. For example, boat will lose something if it has an angled drive like mine does -- such gears are more lossy -- but car has as one of its sets of gears a bevel gear which is also a bit more lossy than a straight helical gear -- these should roughly cancel each other out.



There is nothing really precise about this, but it's a really good data point and makes it awfully hard to imagine that a boat gearbox can be much less than about 95% efficient.


And it works well on the converse side too: If a car drive train with 2.5x the number of bearings and 3x the number of gears and 2x the number of sumps can be 88% efficient, then how can a boat gearbox be 85% efficient?





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Originally Posted by bridaus View Post
Ahh, one of my sources, but doesn't include bearings, churn, or load. Also, what efficiency are you assuming for the helical, 98 or 99 (if you only rely on this source)?

My only point in bringing this up was to show that it ROUGHLY lines up. A percent or two for a set of gears, a percent or two for 4 bearings, and a percent or two for churning -- adds up to roughly what we would expect if we think a boat transmission is roughly 95% efficient.
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Old 22-12-2018, 10:10   #1797
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
I'm asking for sources. You state that you have directly experienced no more than five percent loss with your transmission. Excellent, please let me know how you experienced it, I am very willing to learn and need sources to pin these numbers down.

No, I stated my experience has followed the performance ratings produced by Yanmar, which include the transmission loss. I track engine hours and calculate fuel used per the graphs, actual usage is always better, i.e., less fuel to fill the tank than calculated.



You apparently have no experience, but yet disagree with Yanmar, disagree with Gerr, and you disagree with my explanation of how fuel consumption tracks load not rpm.


Not sure what sources you are looking for...??
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Old 22-12-2018, 10:31   #1798
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Re: Oceanvolt Hybrid Motor

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Well, no one said they aren't putting out heat. 3% loss out of 75kW is still 2.25kW. Out of 20kW it's 600 watts. That's not nothing.

But 15% loss would be 12.5kW and 3kW respectively. I think it's an absolutely fair observation that you can feel that our gearboxes are just not putting out that kind of heat. A little box like that just can't be taking in 3kW and still be lukewarm to the touch.
The manual says that the typical operating temperature is 50-80C or 122 to 176F. That doesn't seem lukewarm to me.
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Old 22-12-2018, 10:37   #1799
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Re: Oceanvolt Hybrid Motor

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The manual says that the typical operating temperature is 50-80C or 122 to 176F. That doesn't seem lukewarm to me.

At full power, sure. At cruising speeds, you can put your hand on most boat gearboxes.
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Old 22-12-2018, 11:00   #1800
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Re: Oceanvolt Hybrid Motor

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At full power, sure. At cruising speeds, you can put your hand on most boat gearboxes.
Hmm, the manual didn't say full power, it said typical. Whatever that means. I think the full power temperature was 100C for "brief periods", also interpretable.

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There is nothing really precise about this, but it's a really good data point and makes it awfully hard to imagine that a boat gearbox can be much less than about 95% efficient.
Great analysis, unitless helps simplify it a bit without losing the point. We don't totally agree on the bearing count, but not to enough of a degree to matter here. I was backing out all the car gear from 88% and getting 95% as well.

This is all assuming this ONE particular study we are using as our input is good, and that we can accurately back out the contributions for the rest of the drivetrain. These are reasonable, but not unassailable assumptions.

I still contend that the efficiency is a little lower than 95% based on straight analysis of the gearbox itself, BUT I need better data than what I have so far. 98 or 99% for a helical gear is quite a wide range in the scheme of things. I do think we are bounding the efficiency, in my mind it's no better than 95% and no worse than 90%, and I've updated the DD/EP model I'm working on to reflect that.
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