Oceanvolt Hybrid Motor

[ssmoot]

Originally Posted by john61ct

Are you saying 1800A discharge is required? At what voltage?

Voltage doesn't matter in this context. Current is what matters. 3C would mean your 7.2kWh pack (presumably, since you said 600ah) could discharge at 21.6kW.

It's more useful to talk in terms of capacity though. kWh. Not ah. Because your motor might be 48V, 72V, 96V, 350V, 360V, etc and a 600ah 360V bank is anything but small.

Which would have made a ton more sense if I hadn't accidentally edited out that I was basing these numbers on a 20kW motor.

Originally Posted by john61ct

The bank has to be so huge per hour of motoring anyway. . .

If you're running a generator that covers 100% of motor needs then you don't actually need very much capacity. But if you want to motor on battery alone you do need to match the capacity/c-rate to the motor (or at least the power level you intend to use it at, but that seems pretty unsafe). ie: Given a 20kW motor and 5kWh battery pack, you need 4C, with a 1kWh pack you need 20C, etc.

My point is that such packs, that are air-cooled, don't exist. At least not in a practical sense. And anything over about 1.5C max is going to suffer from longevity issues. Which means for something like the Torqeedo 48-5000 you need at least three batteries (15kWh) to move the boat on battery power alone.

> And you'd lose all the weight, volume, luxury benefits.

In the monohull vs multihull scenario.

You buy a brand spankin' new Fountaine Pajot. The bigger generator is a marginal weight increase over the standard one. Batteries are a wash depending on your choice. The electric motors are much lighter than the diesels they'd replace. Overall the EP solution should be around 100kg to 200kg lighter. So there's the weight benefit. And on a multihull I understand that's more meaningful.

Then there's volume. The generator is marginally larger, but it probably doesn't impact your stowage given the location. The batteries might take up 50% more space, but again, you're probably not hurting for space on most boats where the batteries are located.

You gain a ton of room in what was formerly your engine bays though (assuming we're talking about electric sail drives or pod drives). If you're using air-cooled saildrives then you probably want a blower hose or something but otherwise you've got a lot of storage volume freed up. Especially appealing on boats with under-bunk engine bays like older Lagoons or the Seawind 1260.

Finally the luxury benefits of running around with a 15kWh battery pack are probably already obvious to you if things like air-conditioning, induction cooking, DC water makers, a small electric hot water heater (to give you the option to get rid of generator use or propane in the interior of the boat), etc appeal to you.

Originally Posted by john61ct

Yes exactly, but I do not understand your point, you seem to be contradicting yourself now ?

When I refer to "mega-batteries", I'm talking about batteries that would let you motor at WoT for 8 hours or more on battery alone. That's garnered a few mentions in the thread. With a 20kW motor you'd need 160kWh. The problem is, you need to put ~167kWh back into it somehow. And you have to typically do it at an average of about 0.5C. So the 10kWh or smaller generator you'd realistically pair with such a system would have to run for 17 hours straight with no propulsion demands if you managed to drain your battery. It just doesn't seem very practical to me, and it would weigh a lot more.

Even if a magical 1lb, 200kWh, $2,400 battery were developed, I'd still be conflicted between that and the 1/4lb 50kWh version for less volume, lower price and a better fit for intended usage when "mains" power is always the flip of a switch away.

Originally Posted by john61ct

> Just get a peak 1C battery pack and call it a day.

I don't know what that means. I don't think I'll be going past .2-3C

I was a bit vague, but it means you need to match your battery output (current) to your peak motor demands. If you're not going to do that, then you'll have to run your generator while running the motor at anything above partial throttle and at that point you might as well direct drive.

Especially on a monohull where you're not recovering any volume. There's a lot of bullet-points in the "Pros" column for EP that go up in smoke if you aren't saving space or weight IMO, and given the cost, that's hard to justify.

[bridaus]

Originally Posted by OldMan

About = 19%!

The 4JH5E @ 2250rpm provides 17KW to the prop. Input of 15KW to the Oceanvolt Servoprop provides 14.25KW to the prop. The 4JH5E will burn less than 5L/hr at this output.

Assume like props, the direct drive will burn less fuel and provide 19% more power to the prop than the OV.

https://www.yanmarmarine.com/theme/y...heet_4JH5E.pdf

I'm concerned with this result, too many assumptions:

• "Same boatspeed" Where are those numbers coming from?
• 17kW to the prop vs 14.25 to the prop: I'm not sure you can compare these numbers at all, how is the 14.25 derived?

Most important: If they are resulting in the same boatspeed then by DEFINITION they are providing the same power to the water.

So also by definition, someone's numbers are off a bit. Either:

• Boatspeeds are not same.
• Power of Yanmar to prop is overstated.
• Power of OV to prop is understated.
• Prop on one or other is much more efficient at this speed
• Some other efficiency/factor I've missed.

Lastly: Fuel consumption is something I don't trust theory on. I have seen too many lies in print. As an engineer you have to do the best you can with theories and hypotheses, but then test the hell out of the actual system in real USE after ponying up the real labor and $$$ to build the theory. Until we get that, we definitely will flap our gums a lot in good clean fun.

[OldMan]

Originally Posted by bridaus

I'm concerned with this result, too many assumptions:

• "Same boatspeed" Where are those numbers coming from?
• 17kW to the prop vs 14.25 to the prop: I'm not sure you can compare these numbers at all, how is the 14.25 derived?

5% loss converting electric to mechanical, 15KW input - 5% = 14.25KW to the prop.


My only point - the DD can deliver 17KW burning less than 5L/hr vs EP consuming 5L/hr for maximum 14.25KW available at the prop.

Originally Posted by bridaus

Most important: If they are resulting in the same boatspeed then by DEFINITION they are providing the same power to the water.

Exactly!

Originally Posted by bridaus

So also by definition, someone's numbers are off a bit. Either:

• Boatspeeds are not same.
• Power of Yanmar to prop is overstated.
• Power of OV to prop is understated.
• Prop on one or other is much more efficient at this speed
• Some other efficiency/factor I've missed.

Lastly: Fuel consumption is something I don't trust theory on. I have seen too many lies in print. As an engineer you have to do the best you can with theories and hypotheses, but then test the hell out of the actual system in real USE after ponying up the real labor and $$$ to build the theory. Until we get that, we definitely will flap our gums a lot in good clean fun.

No doubt, until empirical results are known, and each boat will be different, the only information we have is manufacturers spec sheets.

I can attest that my (2) 3GM30s at cruise rpm producing up to 20KW at the props burn 4-4.5L/hr (total), which quite well may indicate less than 20KW consumed by the props at cruise rpm. Fuel burn is a reflection of load not rpm. Manufacturer spec sheets only show maximums for a given rpm during lab testing.

[bridaus]

Per suggestion by tp12, I built an assumption list to see if it helps with discussion. Also I listed some basic efficiency calculations.

Definitions

• DD=direct drive, EP=Serial electric propulsion

Assumptions:

• New build
• Normal hulls and configurations, nothing exotic.
• Saildrive not counted: Because it is the same in EP/DD.
• Reserve: Optional, but can be included as desired. No rule of thumb yet for me.
• Gearbox Loss: 3-15% per Gerr.
• DC Alternator/Generator loss: 3-15% per research.
• DC Motor loss: 3-15% per research, includes controller/distribution.
• No duty cycle considerations yet, working out how to include.
• No prop considerations yet. EP might be able to gain here with torque at low RPM and CPP has to be considered see below.
• No battery loss considerations yet, I want to optimize by planning the least amount of charging in/out of batteries FIRST and if it can be shown to be negligible by targeting generation power to cruising power...
• No regen/solar/wind considerations yet, too many choices of sizing/efficiencies. This is bonus frosting that I believe makes the cake great, but everyone has different tastes.

Notes:

• Yes, it looks weird to me too that all efficiency claims are 3-15%. I want better numbers, but these are what I'm finding so far that are current and have reasonably trustworthy sources. I think the low is artificially 15% because everything worse is not considered/thrown away and I think the high of 3% might be because it's not worth the engineering $$$ or liability to design for or market for higher. You have to prove and warranty higher, and that last 3% is a &$%# in any engineered system.
• CPP: Leaving it out for now, but only because it needs a side discussion. It's very interesting in my research. It is effectively a transmission, similar to hybrid as a transmission (allows us to leverage the bsfc map better). It may get included later because this is a new build, no reason not to investigate it's effects on DD and EP.
• DC Motor includes controller and distribution
• DC Gen: Contrary to intuition is MORE efficient the more you load it. This is promising for efficiency gains for when something likes to be loaded, we can plan and cycle our loads and save.
• $$$ buys efficiency for both systems, so that's a factor that is hard to control for...
• Not sure how Gerr gets his gearbox efficiencies, need to investigate.
• Time is the great equalizer. I see posts with examples from research vessels and other systems. Real world is good, but in technology things often move fast. Controller and motor efficiencies have climbed in recent years with developments for commercialization of electric cars being applied. It's almost like when an industry is forced to do something (reduce emissions), the side benefits (efficiency) are tangible and usable.
• Engine mfg's should be forced to publish bsfc maps. It makes this so much harder to estimate/calculate. The graphs in most manuals are rubbish, showing you only what the mfg wants you to see (understandably, but still frustrating).

My current comparative math from the above estimates (I expect this will change):

DD losses: 3-15%
EP losses: 8-24%

Difference of 5-9% theoretical efficiency at this stage. Could probably call this 7% difference and feel good about it. This is not a lot, and I believe this can be made up by EP duty cycle, prop optimizations, but I haven't proven that yet to myself let alone anyone here. I only know they do it in large scale operations regularly, so that means it COULD be possible.

Todo:

More prop and CPP research.
More efficiency research, qualify and justify the high and low efficiencies.
Duty cycle research.
More...

Edit: I use generator a lot of places, but I believe it's often an "alternator" that is being used in these DC "generators". The difference is not lost on me, and I'm not sure which term is better to use most generally to keep people on the same page. Regardless, efficiency is efficiency and sometimes I don't care how the power is made, just looking for the output versus the input.

[bridaus]

Originally Posted by OldMan

My only point - the DD can deliver 17KW burning less than 5L/hr vs EP consuming 5L/hr for maximum 14.25KW available at the prop.

I think we are on the same page, we don't know enough to know whether this statement is true. Both depend on calculations that we don't have enough information to guarantee.

[OldMan]

Originally Posted by bridaus

I think we are on the same page, we don't know enough to know whether this statement is true. Both depend on calculations that we don't have enough information to guarantee.

Not sure what your are missing.


BigBeakie provided data on the efficiency of his chosen generator (93%), his fuel usage calcs look reasonable.


The math is very generous giving OceanVolt a 95% efficiency rating, on their own website they only claim 93% efficient.


https://oceanvolt.com/faq/my-first-faq/


Data on the 4JH5E engine is from Yanmar engineers and shows maximum power capability and maximum fuel usage.

[bridaus]

Originally Posted by OldMan

Not sure what your are missing.

BigBeakie provided data on the efficiency of his chosen generator (93%), his fuel usage calcs look reasonable.

The math is very generous giving OceanVolt a 95% efficiency rating, on their own website they only claim 93% efficient.

https://oceanvolt.com/faq/my-first-faq/

Data on the 4JH5E engine is from Yanmar engineers and shows maximum power capability and maximum fuel usage.

I understand what you are saying, I don't doubt your reading of the graphs. I'm not sure it's your error, but there is an error somewhere. You observe the 4JH5E DD is providing 17kW and OV is providing 14.25kW (both to the prop) and both are producing same X boatspeed according to BB. This is impossible unless the OV propping is (17-14.25)/17=16% more efficient. Is that reasonable or possible?

In other words, how are they achieving the same speed with the OV providing less power? It makes no sense to me. I question one or more of the inputs and therefore the results.

[bridaus]

Correction: In my spreadsheet assumptions, I have DC Generator as:

DC Alternator/Generator loss: 5-10% per research, not 3-15%, cut and paste error.

Which still results in 8-24% for EP, 5-9% difference, average of 7%.

[OldMan]

Originally Posted by bridaus

I understand what you are saying, I don't doubt your reading of the graphs. I'm not sure it's your error, but there is an error somewhere. You observe the 4JH5E DD is providing 17kW and OV is providing 14.25kW (both to the prop) and both are producing same X boatspeed according to BB. This is impossible unless the OV propping is (17-14.25)/17=16% more efficient. Is that reasonable or possible?

In other words, how are they achieving the same speed with the OV providing less power? It makes no sense to me. I question one or more of the inputs and therefore the results.

Ah, OK, now I understand. I didn't think thru it that far.


Edit: More thought: If they use the same prop pitch to rpm ratio, the DD may in fact be consuming only 14.25KW from the 4JH5E at the same speed. In that case, the DD would be more efficient as the fuel usage would go down.

[john61ct]

Originally Posted by ssmoot

Voltage doesn't matter in this context. Current is what matters. 3C would mean your 7.2kWh pack (presumably, since you said 600ah) could discharge at 21.6kW.

It's more useful to talk in terms of capacity though. kWh. Not ah. Because your motor might be 48V, 72V, 96V, 350V, 360V, etc and a 600ah 360V bank is anything but small.

Again, fundamental paradigm shift in your thinking required here. Sounds like you perhaps missed the description above in #1657 of my use case. http://www.cruisersforum.com/forums/....php?p=2781452

Take that 7.2kW House bank out of the picture for anything EP related, other than near-realtime buffering of some diesel gennie output fluctuations.

That genset will need be running in order to do any serious EP motoring, and will be sized to handle WOT without any contribution from stored battery power.

The battery will not be operating anywhere near 1C, ideally normal will be .2-.3C in or out for longevity. House loads only.

> And you'd lose all the weight, volume, luxury benefits.

I have no interest in luxury, certainly nothing like aircon. Freezer / fridge yes, via large holding plates, and eliminating propane would be nice but not critical.

Space on my heavy small monohull boat will be so tight, maybe **none** of this is possible. There never was room for a genset other than maybe a Honda in the lazarette to be deployed in the dink.

The **critical** advantage of EP in my use case is **I hope** it will make diesel electric feasible for running the (heavy for such a small boat) House loads.

Hopefully weight will not be so much an issue.

[john61ct]

Originally Posted by OldMan

At that point, the ROI on the upcharge to EP goes way out of whack! You could hire a tug to pull your boat to the next destination and still save $$ over a 10 year period.

Well I still need the genset.

I don't have room for two diesel engines.

I don't need a big bank.

I could go for a small diesel genset, then use an outboard for propulsion I suppose, whatever flavour of dino juice.

But I prefer to imagine upsizing the gennie enough to be able to do EP.

[BigBeakie]

Bigger prop on the OV spinning at same rpm?

It commonly uses a 17.5" Gori or Flexofold for the SD15, and their own variable pitch Servoprop is 18.7" (475mm).

My data inputs are admittedly limited, until we get more data from OV users that are out there, with the specifics of the use in calm water; kW used, boatspeed, prop used etc.

I compared owner reports from a Freeflow 46 with Yanmar 54HP 4JH5E's and 8 years experience cruising with them > 7 knots on one engine at 2250 rpm , and a Slyder 47 with SD15, 7 knots using 15kW. They are very comparable boats wrt hull shape, Lwl/Bh, Displacement. The Freeflow has daggerboards and they were up. The Slyder has mini keels. So hull resistance I'm taking as being very similar, apples to apples.

I looked at the propeller power curve for the Yanmar, as being about 17kW, is that correct?

[bridaus]

BigBeakie could you spell out on two lines each separate configuration (not even sure if it's two actual and one theoretical?) and stats including props, engines, speeds, hull, etc. I'm not able to understand them clearly, I feel like I'm mixing, might just be my reading comprehension.

Thanks!

[valhalla360]

Originally Posted by john61ct

The Reserve Power for Safety issue

How much is "needed" is impossible to quantify as a generality.

No one can predict what you will encounter, the skillset of the captain in avoiding trouble is even more a variable than the "hull strength / build quality" or "RTW bluewater vs weekender hugging coasts" factors.

Plenty of sailors make do with zero "emergency power" it is true, but these days - just like camping discomfort in tiny cabins - that is much less mainstream.

While it's true you can't come up with a specific power needed down to the nearest watt...that's like saying you can't know the maximum load on a bridge.. so just design for the typical loading...

How it works is you make some reasonable assumptions about the conditions you expect to be able to handle and how much power you need to handle them.

But ABSOLUTELY YOU NEED TO KEEP THE ASSUMPTIONS THE SAME FOR BOTH POWER PLANTS.

[valhalla360]

Originally Posted by 44'cruisingcat

Multihulls don't have a hull speed.

Cats do have a hull speed. Some really fast ones, are so far outside the normal range that it seems as if they don't...but if it really bothers you pick a performance speed that the boat needs to determine motor size requirements.