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Old 14-12-2018, 10:46   #1651
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Dockhead View Post
Indeed. So it's a problem which cars have, which hybrid drive with regenerative braking partially solves. A significant hybrid benefit which does not apply to boats.
Wearing a bullet proof vest when getting shot at is a nice thing. It's even nicer to not get shot at.

At a constant 20MPH (minimal drag) regenerative braking isn't used at all. And yet hybrid vehicles, not stopping, traveling at a constant speed are at their most efficient under those conditions.

Can you present a single case of regenerative braking improving range vs maintaining a constant speed covering the same distance?

If not, why confuse the issue? Stop comparing a boat to city driving, where regenerative braking has some benefit (though not nearly as significant as believed here), and start comparing it to constant-speed/efficiency graphs. Then the only difference you need to account for is the drag of the liquid the vehicle is moving through to justify your conclusions.

They are both vehicles moving through a liquid. The only difference is mass, viscosity and thrust. Regenerative braking is an off-topic distraction to that. If your argument is that it's not possible for a boat to achieve the efficiencies a hybrid vehicle does under those conditions, you have to have some other explanation for it besides regenerative braking when you eliminate braking entirely.
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Old 14-12-2018, 11:06   #1652
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Oceanvolt Hybrid Motor

When you want to go slower than normal a hybrid system can do it more efficiently than mechanical.

So what?
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Old 14-12-2018, 11:22   #1653
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Re: Oceanvolt Hybrid Motor

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Originally Posted by transmitterdan View Post
When you want to go slower than normal a hybrid system can do it more efficiently than mechanical.
I certainly didn't make those claims. Citation needed?
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Old 14-12-2018, 11:52   #1654
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
Until you reach hull-speed. Then it might actually be more efficient to store excess energy instead of using it to "climb hills".

.
Multihulls don't have a hull speed.
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Old 14-12-2018, 11:58   #1655
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
Stop comparing a boat to city driving, where regenerative braking has some benefit (though not nearly as significant as believed here), and start comparing it to constant-speed/efficiency graphs. Then the only difference you need to account for is the drag of the liquid the vehicle is moving through to justify your conclusions.

They are both vehicles moving through a liquid. The only difference is mass, viscosity and thrust. Regenerative braking is an off-topic distraction to that. If your argument is that it's not possible for a boat to achieve the efficiencies a hybrid vehicle does under those conditions, you have to have some other explanation for it besides regenerative braking when you eliminate braking entirely.
You have stated this many times, in different ways.
Your point is good, but you might have missed the reason you keep seeing the topic.
Upthread, in defense of an EP boat, it was suggested that boat stops and starts are an important component of the comparison vs a direct drive diesel boat. Most cruisers understand how actually trivial this is, and they don't need to understand algebra for that.
It would indeed be nice to move on to the constant speed efficiency comparison.
Regarding this steady state efficiency between EP and DD, I have yet to see any data that disproves what many have stated: it appears to be close to a wash after dispensing with propeller confusion and other distractions.
I'm still in, though, and not for efficiency.
It's all about controlling the noise for me... the redeeming quality.
As for the efficiency....
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Old 14-12-2018, 12:19   #1656
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Re: Oceanvolt Hybrid Motor

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Originally Posted by 44'cruisingcat View Post
Multihulls don't have a hull speed.

Multihulls do have a hull speed.


As Froude defined it, briefly; the speed where applying extra power starts to dig a hole in the water, instead of linearly increasing speed. Of course this only applies to displacement hulls. Most multis.
Froude's formula ignores the effect of l/b ratio on hull speed. Which made sense in his day, when all vessels were monohulls, with similar l/b ratios.

Multihulls do have a hull speed, but, because of l/b ratios of 10, or greater, it is much higher than an equivalent monohull.
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Old 14-12-2018, 12:21   #1657
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Re: Oceanvolt Hybrid Motor

For me fuel efficiency is not a high priority as long as within the ballpark.

Cost, weight & space maybe seems the biggest obstacle. How big an electric motor do I need?

Monohull only, 6-10,000# displacement, 26-31' length,

want 5-6 knot calm cruising,

say 30% reserve HP at WOT for SHTF?

Do not plan on a huge battery bank, maybe 600aH LFP, not much alt-energy input expected.

Weight savings are obviously very important, already needing at least a small diesel genset is a given.
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Old 14-12-2018, 12:41   #1658
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Re: Oceanvolt Hybrid Motor

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Originally Posted by KJThomas View Post
Multihulls do have a hull speed.


As Froude defined it, briefly; the speed where applying extra power starts to dig a hole in the water, instead of linearly increasing speed. Of course this only applies to displacement hulls. Most multis.
Froude's formula ignores the effect of l/b ratio on hull speed. Which made sense in his day, when all vessels were monohulls, with similar l/b ratios.

Multihulls do have a hull speed, but, because of l/b ratios of 10, or greater, it is much higher than an equivalent monohull.
Ok, so what's the formula? Ive seen 50 foot cats doing 30+ knots in full displacement mode, not planing. Our 44 footer has touched 25.

And the fact is, the bow wave at those speeds isn't noticeably bigger than at 10 knots.
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Old 14-12-2018, 12:52   #1659
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Re: Oceanvolt Hybrid Motor

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Originally Posted by cyan View Post
You have stated this many times, in different ways.
Your point is good, but you might have missed the reason you keep seeing the topic.
Upthread, in defense of an EP boat, it was suggested that boat stops and starts are an important component of the comparison vs a direct drive diesel boat. Most cruisers understand how actually trivial this is, and they don't need to understand algebra for that.
It would indeed be nice to move on to the constant speed efficiency comparison.
Regarding this steady state efficiency between EP and DD, I have yet to see any data that disproves what many have stated: it appears to be close to a wash after dispensing with propeller confusion and other distractions.
I'm still in, though, and not for efficiency.
It's all about controlling the noise for me... the redeeming quality.
As for the efficiency....
Starts and stops are important yes, but not because regen is a factor. To me regen does not seem as promising on boats because they simply do not need to "throw away" speed, water is much more viscous than air. There are not many times where you need to waste energy (heat in brakes in cars) to slow a boat.

Starts and stops are important because I think they make up more engine hours fleet wide than people think.
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Old 14-12-2018, 12:55   #1660
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by cyan View Post
it was suggested that boat stops and starts are an important component of the comparison vs a direct drive diesel boat
I definitely missed that.

Quote:
Originally Posted by cyan View Post
It would indeed be nice to move on to the constant speed efficiency comparison.
Agreed. It feels like with the right math this could all be put to bed and everyone could walk away happy feeling like they've learned something.

Quote:
Originally Posted by cyan View Post
it appears to be close to a wash after dispensing with propeller confusion and other distractions.
I think there's potential to do the same as cars. Use a (typically smaller) engine that operates at peak efficiency, overcoming conversion losses compared to using a bigger direct-drive engine inefficiently. Make it just big enough to provide for typical power requirements plus some margin to slowly charge the battery.

But I'd also agree that the overall efficiency advantage is probably very small (under 10% I'd guess) and there'd probably be bigger gains from manufacturers just building better, more modern engines.

If you're going to use electric motors anyways it's a nice to have.

My only issue with the efficiency topic is the unsupported claim that overall efficiency would go down when that flies in the face of all available evidence.

Quote:
Originally Posted by cyan View Post
I'm still in, though, and not for efficiency.
It's all about controlling the noise for me... the redeeming quality.
Agreed. There are a lot of reasons to prefer EP I think. Efficiency is way down the list. I just don't think there's any evidence to move it into the "Cons" column.

In fact, I can think of only two Cons (though I'd love to hear more):
  1. Repower/Upgrade Cost
  2. Redundancy

Maybe someday I'll find a Seawind 1260 that needs a repower at a steep discount.
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Old 14-12-2018, 13:17   #1661
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Re: Oceanvolt Hybrid Motor

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Originally Posted by john61ct View Post
For me fuel efficiency is not a high priority as long as within the ballpark.

Cost, weight & space maybe seems the biggest obstacle. How big an electric motor do I need?

Monohull only, 6-10,000# displacement, 26-31' length,

want 5-6 knot calm cruising,

say 30% reserve HP at WOT for SHTF?

Do not plan on a huge battery bank, maybe 600aH LFP, not much alt-energy input expected.

Weight savings are obviously very important, already needing at least a small diesel genset is a given.
Time for fun!

According to quick calculations, most losses not calculated yet (lots of opportunity to be wrong):

28ft
10K#
30% reserve
5.5 kt normal cruise at slightly less than 10hp (30% reserve = 3hp, but we'll do more).
8.4 kt max at 50hp, but won't size for this wasteful speed unless you wanted to, but you said you wanted 30% reserve, not 400% reserve.

Size the electric motor at 10kW (20-25hp equivalent)
Size the DC genny at 5kW continuous (might require a 6kW to get cont. 5kW, oversized for normal cruise)
600ah *12v (assumed) = 7.2kWh

5.8kt conservatively as long you have fuel, and 7.0kts conservative for 30 minutes (based on size of your bank).

1.65 liters per hour using Polar fuel consumption at 5kW continuous, but I don't believe them, they call them "calculated". Call it 2 or 2.5, I think it's still good.

I put in some conservatism in this, but I did it so fast I guarantee it is wrong I did it for fun and as a starting point.
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Old 14-12-2018, 13:21   #1662
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Re: Oceanvolt Hybrid Motor

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Originally Posted by john61ct View Post
Do not plan on a huge battery bank, maybe 600aH LFP, not much alt-energy input expected.
That's a sticking point. I haven't seen a LiFePO4 bank yet that's that small that has a ~3C rate. Air cooled batteries just don't have those kinds of continuous c-rates without severe degradation issues. Even NMC is going to want 0.5C charge, ~1.5C discharge for longevity if it's air cooled.

So you'd have to plan on firing up your generator before you could motor.

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

You're definitely better off with diesel direct drive at that point I think.

Battery capacity isn't the bottleneck in EP. By the time you can match charge/discharge rates to your power needs, you already have a lot of capacity.

While I've seen some comments that dream about more capacity and waiting for some revolutionary tech to enable it, I don't think that's practical. As someone who drives around with a 60kWh battery, what I want is not more capacity. It's more fast chargers along travel routes. I don't want to drive around with a battery I'll typically only use a few percent of. Unless that capacity can do 100% of the job, it just means fewer, but much longer stops.

Same on a boat. You could have a 200kWh battery. But do you want to run your generator for 36 hours straight to charge it back up? If you're motoring for the day, better to be running your generator if the dead zone lasts for more than an hour or two.

I'm not going to call it stupid or anything. But as someone who lives with electric transportation every day, I don't understand the rationale for wanting mega-batteries and carrying all that extra weight and losing all that volume in your boat and wallet. There's definitely a happy medium, and it feels like we're already there with current C-rates. Just get a peak 1C battery pack and call it a day. Can anyone think of a reason for more than that?
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Old 14-12-2018, 13:55   #1663
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Re: Oceanvolt Hybrid Motor

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Originally Posted by ssmoot View Post
That's a sticking point. I haven't seen a LiFePO4 bank yet that's that small that has a ~3C rate. Air cooled batteries just don't have those kinds of continuous c-rates without severe degradation issues. Even NMC is going to want 0.5C charge, ~1.5C discharge for longevity if it's air cooled.

So you'd have to plan on firing up your generator before you could motor.

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

You're definitely better off with diesel direct drive at that point I think.

Battery capacity isn't the bottleneck in EP. By the time you can match charge/discharge rates to your power needs, you already have a lot of capacity.

While I've seen some comments that dream about more capacity and waiting for some revolutionary tech to enable it, I don't think that's practical. As someone who drives around with a 60kWh battery, what I want is not more capacity. It's more fast chargers along travel routes. I don't want to drive around with a battery I'll typically only use a few percent of. Unless that capacity can do 100% of the job, it just means fewer, but much longer stops.

Same on a boat. You could have a 200kWh battery. But do you want to run your generator for 36 hours straight to charge it back up? If you're motoring for the day, better to be running your generator if the dead zone lasts for more than an hour or two.

I'm not going to call it stupid or anything. But as someone who lives with electric transportation every day, I don't understand the rationale for wanting mega-batteries and carrying all that extra weight and losing all that volume in your boat and wallet. There's definitely a happy medium, and it feels like we're already there with current C-rates. Just get a peak 1C battery pack and call it a day. Can anyone think of a reason for more than that?
In the example I'm quick calculating a 0.6C charge rate with 5kW genny (and that's only if battery pack is fully empty and you want it full fast). Unless I'm missing something.

Even so, why does everyone always assume their tank is empty?

A small electric car story: Everyone always asks me how long it takes to charge my car. Answer: I don't really know, I plug it in every night and in the morning, it's full. I park at the "gas station" every night. (Ok, I do know out of interest, but not out of need, but my answer is better). Yes, I know we are not parking the boat in a garage, but I'm not also waking up, discovering I'm clawing my way off a lee short AND my battery bank is dead empty (unless I plan to prepare horribly, and then I should prepare for lack of preparedness by buying more reserve, but I sense a disturbance in the force in my planned lack of planning... hmm).
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Old 14-12-2018, 14:29   #1664
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Re: Oceanvolt Hybrid Motor

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Originally Posted by bridaus View Post
In the example I'm quick calculating a 0.6C charge rate with 5kW genny (and that's only if battery pack is fully empty and you want it full fast). Unless I'm missing something.
I was using 20kW motor as the baseline. Your 10kW number may be more realistic.

Quote:
Originally Posted by bridaus View Post
Even so, why does everyone always assume their tank is empty?
I'm not assuming that. C-rate doesn't depend on SoC. If you don't have enough C-rate to meet your discharge requirements you need to run the generator or risk damaging the pack.

Quote:
Originally Posted by bridaus View Post
A small electric car story: Everyone always asks me how long it takes to charge my car. Answer: I don't really know, I plug it in every night and in the morning, it's full. I park at the "gas station" every night. (Ok, I do know out of interest, but not out of need, but my answer is better). Yes, I know we are not parking the boat in a garage, but I'm not also waking up, discovering I'm clawing my way off a lee short AND my battery bank is dead empty (unless I plan to prepare horribly, and then I should prepare for lack of preparedness by buying more reserve, but I sense a disturbance in the force in my planned lack of planning... hmm).
Totally agree. The best thing about an EV is never visiting a gas station (and the performance, and the TCO, and... well, you get the idea ). And even though I have no reason to feel anxious, I rarely let mine go lower than 50% SoC. I couldn't imagine owning an EP boat and not keeping the pack around 80% as a general rule. Maybe if I felt like running the air-conditioning I'd plan to let it get down to around 40% by morning, but I'd still check the forecast before going to bed.

My pack lives between 50% and 90% pretty much all the time. I've only had it down to ~10% once, when I calculated I could skip the last charge station on a road trip back home and still have ~15 miles in reserve. I can't imagine that being any different on a boat. Force of habit I guess.

In a perfect world I'd have digital switching and just turn on the generator automatically once SoC hit 40% and stop it at 80% (for battery longevity and charge efficiency). And automatically turn off power to all non-essential devices besides propulsion if power ever hit 30%. In fact, if I could figure out a way to pack in 3kW of solar, I'd probably just skip the diesel generator entirely and carry a pair of parallel gas generators for peace of mind.
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Old 14-12-2018, 19:41   #1665
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Re: Oceanvolt Hybrid Motor

Nice to see some analysis on EP Hybrid vs DD by both sides. At the end of the day, this is a topic that can be resolved, because it comes down to demonstrable facts, not agenda driven opinions.

Just wanted to point out and share the DC genset efficiency re fuel useage mistake I was making, and that has been corrected by the head engineer of Eniquest who makes our DC genset.

The engine charts for Yanmar fuel used vs RPM ( and probably all other marine diesels for the common sizes for sailboats) is only applicable for direct propulsion use, not when used as the power plant for gensets.

So for our DC genset we take the given fuel use per kWh power produced times the kW produced as output, which is 260 grams diesel per kWh produced, divided by the efficiency of the alternator, which in our case is 93% to give the total fuel used in grams per kWh. Then to convert to liters per hour AT THAT POWER OUTPUT divide by specific gravity of the diesel or 830.

So our 16kW DC genset from Eniquest produces 15kW so:

(260g/kWh x 15kW) divided by .93 = 4194 grams of diesel. Divided by 830 = 5.05 liters per hour to produce 15kW.

At half power producing 7.5kW we'd use 2.5 liter per hour of diesel.

When I compared that to the designers recommended Yanmar engine for the same boat, the 4JH5E Series, I see that that at the cruising rpm for that engine (2250) to give the same boatspeed as the Servoprop 15kW, the kW output is about the same and fuel useage is about the same.
So, it's a wash on direct drive diesel vs electric hybrid as far as I can see.

My conclusion way back then when I worked through this with the help of a marine engineer experienced in sizing engines for sailboats, as it is now, is that the cruising speed performance is about the same between the two options, ie the 15kW Oceanvolt Servoprop and the Yanmar 54HP (40kW).

The Yanmar 4JH5E will give a higher top speed by about a knot to 1.5 knots on the same boat when its at WOT.

Nothing I have seen or heard, whether on this forum, or otherwise, has changed what I saw way back then, and when I posted that you need a diesel approximately 2 to 3 times larger than the OV 15kW to get the same cruising speed. And it seems, some other OV users are reporting the same conclusion on this forum.

Here is a paper on the benefits and system considerations for the rationale for electric hybrid. Note that it is from a marine diesel manufacturer, Man Diesel.
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