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Old 12-02-2018, 20:04   #1216
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Re: Oceanvolt Hybrid Motor

Valhalla your numbers are more than suspect they are jokes. 4-5kw is not going to move a sizable boat at any speed. So unless you are going to be cruising around in a canoe you are just wrong.

Saying Lifepo is only double the cost is absolutely absurd. Maybe if you buy bottom of the barrel reject batteries with no BMS. But a Renogen 12v 100ah Lifepo runs $850-1,000 a piece. So for your $5,000 you get all of what, 6 of them, or ~7.2kwh, even with 100% dod thats less than an hour of run time. Let me know where you get better prices, I would be happy to take a look. Or go really name brand with Mastervolt and you can get 320ah @12v for $7,000.

The rest is just equal nonsense and wishful thinking. EP is workable on small craft going short distances with regular access to shore power. But for any real size or distance it just isn't there. The problem is one of energy density. There is roughly 1/50 the power in a pound of LifePo batteries as there is in a pound of diesel. Until that problem is solved it just won't work.
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Old 12-02-2018, 20:20   #1217
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Re: Oceanvolt Hybrid Motor

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Originally Posted by Stumble View Post
Valhalla your numbers are more than suspect they are jokes. 4-5kw is not going to move a sizable boat at any speed. So unless you are going to be cruising around in a canoe you are just wrong.
The 25hp we had at barely over idle would get us 4mph. 5mph wasn't much more throttle. That should work out petty close to 5kw for 5mph. No wishful thinking--- actual experience.

A replacement Leaf battery pack is $5500 with 24kwh usable power. If you want to do a DIY aftermarket, it likely would run higher but a manufacturer buying in bulk could likely get something pretty close.

So far, you haven't provided much to challenge the assertion that it's viable for a canal cruiser where the energy density issue largely goes away.

You might need to tweak the specs and costs a little but the numbers do work.
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Old 12-02-2018, 21:53   #1218
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Re: Oceanvolt Hybrid Motor

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Yes, you are correct. I was thinking more of keeping the hull geometry constant, where a boat of more displacement would have a waterline length multiplied by the cube root of change in displacement. And in this case, the wetted area would increase with an exponent of 2/3 (or the square of the cube root). So even then it's not linear, but it is significant. Double the displacement, and the wetted area is multiplied by 1.59 (approximately).
In that case the drag at a given speed is not exactly proportional to wetted area, as changes in Reynolds number are also present, but rather small. And if you were considering mostly wavemaking drag, then it's only valid when Froude number is kept constant and speed is not. Only in that case wavemaking drag of a given shape (but changing size) is proportional to displacement.

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In the case you are actually considering, where the additional displacement is only increasing the draft of an existing floating shoebox (so to speak), then the wetted area may change very little.
I thought that to be the case for most canal boats I have seen, when loaded up more.
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Old 14-02-2018, 10:45   #1219
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Re: Oceanvolt Hybrid Motor

I tried sifting through these 80 + pages for the answer I'm looking for, perhaps I missed it but I didn't see it directly addressed.

What would be more fuel efficient, say on a 45-foot catamaran, standard 50+ hp motors with sail drives or replacing both the motors with two smallish generators say 6-9 kw ones and replacing the sail drives with pod type electric sail drive.

The advantage I see are you don't need another generator so your down to 2 motors vs. 3. So saving a bit of weight. Also in my mind the electric pod drive would be more effecient vs. mechanical sail drive. Not sure if you would have to go bigger than 9kw generator to get equivalent power, if more maybe 13kw generators?

Anyway, cost aside, what would use less fuel at crusing speed assuming you were able to match similar power to move the boat at the same speed?
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Old 14-02-2018, 11:59   #1220
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Re: Oceanvolt Hybrid Motor

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Originally Posted by rpmbnsf View Post
I tried sifting through these 80 + pages for the answer I'm looking for, perhaps I missed it but I didn't see it directly addressed.

What would be more fuel efficient, say on a 45-foot catamaran, standard 50+ hp motors with sail drives or replacing both the motors with two smallish generators say 6-9 kw ones and replacing the sail drives with pod type electric sail drive.

The advantage I see are you don't need another generator so your down to 2 motors vs. 3. So saving a bit of weight. Also in my mind the electric pod drive would be more effecient vs. mechanical sail drive. Not sure if you would have to go bigger than 9kw generator to get equivalent power, if more maybe 13kw generators?

Anyway, cost aside, what would use less fuel at crusing speed assuming you were able to match similar power to move the boat at the same speed?
I suppose it depends on what you are trying for. 100 hp (2 x 50 hp) on a 45' catamaran is a lot of power, and more than you need in typical conditions. It's even more than you need in relatively challenging wind and seas. My 44 ft heavy monohull only has about 50 hp total. Your cat may have more windage than my boat, so that may be driving the hp choice.

But the electric pods aren't any more efficient than diesel, when you need to deliver hp to the prop, and this is where people start believing in magic. Assume you actually need 14 hp total to reach a 7 kt cruising speed in zero wind and flat seas (7 hp per prop). You could install two small diesels, or keep the 50 hp models. When running lightly loaded diesel engines burn proportionally less fuel, so the "diesel inefficiency" isn't really that much of a factor.

Or you could install two 12kW motors, which will deliver about 7 hp at each prop after the controller and motor losses. You will need at least a 24 kW generator at this power level (and we actually want bigger motors and generator for margin).

That 24 kW generator will have similar fuel efficiency (per hp delivered) as would your diesel engines. Then you have to allow for the losses in the generator / controller / motor chain, which might be worse than 80% I suspect that the diesel fuel consumption would actually be better with even the 50 hp engines, and the 50's would give you much more margin should you need it. The cheapest solution would be to go with diesel engines, sized for your requirements. If you don't want the extra power margin, use smaller diesels.
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Old 14-02-2018, 13:14   #1221
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Re: Oceanvolt Hybrid Motor

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Originally Posted by rpmbnsf View Post

Anyway, cost aside, what would use less fuel at crusing speed assuming you were able to match similar power to move the boat at the same speed?
This is the problem. You wouldn't be able to move the boat at the same speed. You're replacing 37 kw motors with 9 kw motors. There will be a loss of performance.
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Old 14-02-2018, 13:21   #1222
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Re: Oceanvolt Hybrid Motor

Hi Paul, thanks for the reply.

Even the new Lagoon 42 come with 45 hp standard and 54 hp as an upgrade. I know, sounds like a lot of hp that may not be needed. I was just trying to hit the typical setup most would see on a boat that size.

As for efficiency, I would have thought the direct drive electric pod would be far more effecient vs. the gearing in the typical sail drive. It looks like oceanvolt is not direct drive pod style but torqeedo puts out one like that. I really do not know what the hp needs at the prop would be to push a ~14 tn cat at crusing speeds but looks like they have some up to 40hp.

If it's not really more effecient that's really to bad, would be great for several reasons, weight savings, cut down on maintenance (no saildrive, two total motors vs 3), instant response in throttle, even into reverse - great for docking. Overall I would think quieter and with less vibration.

Edit: Looks like on their site (torqeedo) they have bigger systems too - 27, 55 or 110 kw output electric motors. And listing up to 20kw generators. Not sure if they have real proof of application, a lot of computer generated images.

Just wish there was some type of test that uses the same boat, motor with sail drive then replace it with a system like torqeedo. What would real world differences be I wonder (cost aside )
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Old 14-02-2018, 14:26   #1223
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Re: Oceanvolt Hybrid Motor

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Originally Posted by rpmbnsf View Post
Just wish there was some type of test that uses the same boat, motor with sail drive then replace it with a system like torqeedo. What would real world differences be I wonder (cost aside )
Possibly the closest you will get to that "test" is to look at the number of hybrid Lagoons that replaced their propulsion with standard diesel.
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Old 14-02-2018, 15:44   #1224
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Re: Oceanvolt Hybrid Motor

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Originally Posted by rpmbnsf View Post
Hi Paul, thanks for the reply.

Even the new Lagoon 42 come with 45 hp standard and 54 hp as an upgrade. I know, sounds like a lot of hp that may not be needed. I was just trying to hit the typical setup most would see on a boat that size.

As for efficiency, I would have thought the direct drive electric pod would be far more effecient vs. the gearing in the typical sail drive. It looks like oceanvolt is not direct drive pod style but torqeedo puts out one like that. I really do not know what the hp needs at the prop would be to push a ~14 tn cat at crusing speeds but looks like they have some up to 40hp.

If it's not really more effecient that's really to bad, would be great for several reasons, weight savings, cut down on maintenance (no saildrive, two total motors vs 3), instant response in throttle, even into reverse - great for docking. Overall I would think quieter and with less vibration.

Edit: Looks like on their site (torqeedo) they have bigger systems too - 27, 55 or 110 kw output electric motors. And listing up to 20kw generators. Not sure if they have real proof of application, a lot of computer generated images.

Just wish there was some type of test that uses the same boat, motor with sail drive then replace it with a system like torqeedo. What would real world differences be I wonder (cost aside )
The problem is you are not comparing apples to apples but apples to airplanes. If you need 40kw at each prop then the electric motors must be twin 40kw motors, and the generator has to be rated at 80kw continuous.

If you are ok with 20kw total from the props then you need to compare a 20kw generator and twin 10kw motors to a diesel that will output 10kw at the prop, likely about 14hp rated.

All of the professional testing that has been done shows that electric can be more efficient for very slow speeds, say less than 3kn. As the boat size grows, or the speed required goes up the efficiency switches in favor of diesels. The reason that most people ignore these very low speeds is because even if the electric is far more efficient at those speeds in relative terms (% fuel saved), it is meaningless in absolute numbers (gallons saved).

This is a pure optimization problem, define the usage of the boat and it is pretty easy to kick out the ideal answer. Under a few very narrow use cases electric is preferable. Under everything else diesel is. The problem is the electric crowd doesn't like this narrow use case so they play fast an loose with the numbers. Things like an electric HP is better... or torque is more important than hp... Any time you see an electric motor replacing a diesel multiple times its size you know something fishy is going on.
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Old 14-02-2018, 15:52   #1225
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Re: Oceanvolt Hybrid Motor

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Originally Posted by rpmbnsf View Post
I tried sifting through these 80 + pages for the answer I'm looking for, perhaps I missed it but I didn't see it directly addressed.

What would be more fuel efficient, say on a 45-foot catamaran, standard 50+ hp motors with sail drives or replacing both the motors with two smallish generators say 6-9 kw ones and replacing the sail drives with pod type electric sail drive.

The advantage I see are you don't need another generator so your down to 2 motors vs. 3. So saving a bit of weight. Also in my mind the electric pod drive would be more effecient vs. mechanical sail drive. Not sure if you would have to go bigger than 9kw generator to get equivalent power, if more maybe 13kw generators?

Anyway, cost aside, what would use less fuel at crusing speed assuming you were able to match similar power to move the boat at the same speed?
This did get talked about multiple times. Search for "magic hp".

If you feel you need a pair of 50hp diesel motors, a pair of 8-12hp motors will be marginal in good conditions and woefully under powered when conditions get tough.

You do gain a little by eliminating the mechanical transmission losses but that is weighed against the losses from converting diesel mechanical power to electric power and then back to mechanical power.

Generally the hybrid is going to have greater losses. Also, if you are running direct off the generators without a battery bank, you don't have that instant power.
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Old 14-02-2018, 17:11   #1226
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Re: Oceanvolt Hybrid Motor

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As for efficiency, I would have thought the direct drive electric pod would be far more effecient vs. the gearing in the typical sail drive.
I think that people may be overestimating the losses in the diesel power train. In his Propeller Handbook, Dave Gerr states that the gearbox loss is about 3%, and about 1.5% per propshaft bearing. This seems compatible with the performance curves that Yanmar gives for their 4JH57 57 hp engine:

And in that chart, do take a look at the fuel consumption vs the propeller power curve (this shows the power actually delivered to the propeller at any given RPM). It looks like the fuel consumption is around 0.3 liters / hour / hp, over a very broad range of RPM. In short, there is not that much extra loss when running a diesel engine lightly loaded at low RPM.

We definitely need to define exactly what losses, or efficiencies, we are considering. But start from the propeller and work backwards. How fast do you have to spin the prop for a given speed? That takes a certain amount of horsepower at the propshaft, and it doesn't matter if the power source is a diesel engine or an electric motor.

Then look at the losses in the transmission and shaft bearings. In a diesel, that may be 5%. Electric with only bearing losses, perhaps 1 or 2% These differences aren't enough to magically turn one hp into three.

Electric motors can deliver huge torque at very low RPMs (or when stalled). Diesels can't. That makes a big difference in a railroad engine, but not very much in a pleasure boat. That's why your internal combustion car has a gearshift, but your boat doesn't. Take a look at the Yanmar propeller power curve and see how little power is required to spin the prop at low RPM -- the diesel can do it with no problem.

Electric motors are very efficient in turning stored electrical power into work -- 90% is fairly common. Diesel engines waste about half the power available in their fuel. But that type of efficiency is vastly overshadowed by the incredible amount of power stored in a liter of diesel fuel. Liter for liter, pound for pound, diesel fuel contains at least 30 times the power of even Lithium batteries. Divide that by two for the diesel system losses and you can still see why electric systems really only compete in a small subset of boat applications.
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Old 14-02-2018, 19:43   #1227
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Re: Oceanvolt Hybrid Motor

I believe Paul's post is one of the clearest supplied on this subject for some time.

It also explains why certain companies have leeway to use partial truths to market their products. It is certainly true that Electric Motors have maximal use of power at low torques, as compared to diesel motors. It is then easy to extrapolate this to imply that at typical usage torque the electric motor will yield significantly greater HP or KW at the prop. This is in fact not correct as the torque graphs indicate. Whilst there may be some difference it reduces as torque increases, right up to maximal rated torque where there is little difference between the two.

In terms of the ability to deliver power to motors, electrical or diesel, then this is simply a matter of energy storage and diesel wins hands down as compared to any current battery technology. Thus to provide equivalent usage of maximum torques large generators are needed which makes cost prohibitive.

In my view if you want an EP boat then you need to start with characteristics of the boat in question and design a boat requiring minimal propulsion energy. Of course you could equip such a boat with small retractable diesel/petrol outboards which would still be cheaper than EP, but at least the required EP would not break the bank.
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Old 14-02-2018, 20:15   #1228
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Re: Oceanvolt Hybrid Motor

Paul,

Nice summary but you made one major mistake on energy density.

Diesel has a energy density of 48MJ/kg, rechargeable Lithium Ion batteries have a maximum energy density of about .5MJ/kg. So the nominal energy density is almost 100 times the best batteries, and the usable energy density is about 50 times LifePo, not 15 times.

The energy density of FLA batteries btw is .17MJ/kg. But since you can only discharge them to 50% its a strait up .17MJ/kg to 50MJ/kg comparison. Is it any wonder why FLA for propulsion is a pipe dream?
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Old 14-02-2018, 22:33   #1229
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Re: Oceanvolt Hybrid Motor

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Paul,

Nice summary but you made one major mistake on energy density.

Diesel has a energy density of 48MJ/kg, rechargeable Lithium Ion batteries have a maximum energy density of about .5MJ/kg. So the nominal energy density is almost 100 times the best batteries, and the usable energy density is about 50 times LifePo, not 15 times.

The energy density of FLA batteries btw is .17MJ/kg. But since you can only discharge them to 50% its a strait up .17MJ/kg to 50MJ/kg comparison. Is it any wonder why FLA for propulsion is a pipe dream?
Not exactly a mistake, but I wasn't too clear. Your energy density numbers are correct when we compare weight of battery vs weight of fuel. But I did say "Liter for liter, pound for pound", and if we compare energy per volume, then my 30x is fairly close. However you look at it, it's a lot.

As for FLA propulsion batteries, you sure are right! I've been helping a friend with an electric propulsion project, where he needs at least 200 kWh from the batteries. He asked about the Firefly carbon-foam batteries, and I figured that it would require about 250 G31 batteries to support that power at high discharge rates. Cost would be about $120,000 for just the batteries. Weight over 18,000 lbs.

Compare that to two of the Tesla 100 kWh battery packs. There's a reason that Tesla is using Lithium.

I think his project will turn out to be completely impractical and never see the light of day, but I keep searching for that magic...
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Old 15-02-2018, 01:17   #1230
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Re: Oceanvolt Hybrid Motor

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In my view if you want an EP boat then you need to start with characteristics of the boat in question and design a boat requiring minimal propulsion energy. Of course you could equip such a boat with small retractable diesel/petrol outboards which would still be cheaper than EP, but at least the required EP would not break the bank.
This is another EV proponent trick. They compare a design that uses a pair of 50hp motors to a much more efficent design that would be happy with say a pair of 20hp motors but they assume the 50hp is diesel and the 20hp is electric and then point to how electric can match diesel.

If you are going to make a more efficient design, the comparison must be with appropriate size diesel or it's a false comparison.

I think it makes far more sense to develop a use case for different types of cruisers and then market to those cruisers.
- Weekenders who rarely do anything but day sail: EV it practical now because 10-20mile range is plenty to get in and out of the harbor and you have lots of time to recharge either with solar during the week or plugged into shore power.

This is where my idea a couple pages back with canal cruisers came from. This is a scenario where emergency power fighting storm conditions is unlikely, running at 50% of hull speed is fairly common, spending an hour or two of a daily run time idling in a lock is common, there is no mast to conflict with a large solar array...The numbers can be made to work to meet typical performance expectations without breaking the bank. It's not going to be a slam dunk based purely on propulsion fuel savings but close enough that you can justify it as an option. Where it can really have some advantages is the side benefits of being able to run air/con and other heavy loads without need of a generator.

Another possibility is houseboats. We did a rental with the family a few years back. It had a single 90hp outboard (60' displacement) and a 4cycl generator. In 5 days, we only covered maybe 20 miles but had a big fuel bill mostly from running the generator. Air draft wasn't a big concern and there was a huge sun shade that could hold a massive solar array. You'd have to work thru the numbers but this could be a scenario where it works out if you spend most weekends hanging out on the hook 5-10miles from your marina.
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