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05-10-2017, 16:36
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#46
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Registered User
Join Date: Mar 2017
Posts: 293
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by Dave_S
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Dave, I'm not questioning your math, but where are you getting the figures of miles traveled per energy expended? I haven't been able to find that information myself yet. I'm not a fan of AGM tech for this as you can really only use half of your AH without hurting your batteries. How did you come up with the figure of 365kwh as a necessary bank size? That's much larger than any of the test boats I've read about configured with a hybrid system.
The cost isn't a concern for me as I believe battery prices will plummet in the next 5 years as I feel the whole world (transportation, home, mobile) will all be using this technology along with solar at an insane scale. I am curious about the real world physical limitations of the size and weight of enough energy to drive a boat 200 miles at 6 knots.
Moonwave is a hybrid cat. Here are her specs:
144V 23KWh Li-FePO4 battery bank
24V 4.8KWh Li-FePO4 battery bank
Fischer Panda 22 KW 144 DC generators (x2)
AC system runs from batteries at night – no generator noise
No doubt this is a demonstration cat to prove the technology and is only intended for easy island hopping.
Full spec sheet can be seen here:
Systems - MOONWAVE - Gunboat 60 Catamaran
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05-10-2017, 18:16
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#47
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Registered User
Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,987
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Re: Solar sails and the future of hybrid cats
Thanks for the link, I'll have a look.
I guestimated you would need a motor output of equal to or greater than 9.5kw to push an efficiently designed lightweight cat along at 6kn in average seas. This a conservative "back of envelope" type calculation and I think you would need more power to run at 6kn after you put all those batteries in :-)
So my math goes like this.....
9.5kw out is at best 11kw in.
6kn for 33 hours gets you 198km - close to your 200
11kw for 33hrs
363kwh
__________________
Regards
Dave
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05-10-2017, 19:29
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#48
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Registered User
Join Date: Sep 2006
Posts: 9,398
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by ssmoot
If what you want to claim is that for you, WOT performance is your primary motivator when sizing diesel propulsion that's great. For you.
I think Oceanvolt's claims are a lot closer to the mark for me than yours though if that's the case.
In general, I think they're overpriced, and may be overstating a bit in their marketing, but I do think the cruising-speed load number is a lot closer to 20hp than 45hp as a rule of thumb.
Regardless, I'm not sure what your point is except to insinuate you don't think 20hp is good enough. If that's the case, don't buy it? If other people are motivated more by finding the system that provides a comparable cruising speed minus the noise and vibration, but with the much bigger battery, why is that a problem for you?
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My point is that Oceanvolt and Torqueedo are dishonest about the capabilities of their products. While none of us runs our engines at WOT for much of the time, 75% power output would be quite commonly used. Assuming the boat has appropriately sized motors. And in some circumstances WOT WILL be used, such as sprinting over a dangerous bar for instance.
Claiming a 20 kw electric motor is EQUAL TO a 33kw diesel is misleading, dishonest, and potentially dangerous.
And these businesses tend to compound the problem by specifying too small generators, often too small to allow ONE engine to operate at even 75% power without draining the batteries.
So if you're prepared to seriously compromise your boat's capabilities, and pay a serious financial premium for doing so, then hybrids make perfect sense.
__________________
"You CANNOT be serious!"
John McEnroe
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05-10-2017, 19:35
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#49
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Registered User
Join Date: Nov 2014
Posts: 261
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by Dave_S
9.5kw out is at best 11kw in.
6kn for 33 hours gets you 198km - close to your 200
11kw for 33hrs
363kwh
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Those seem like very reasonable if not overly generous (in favor of electric) numbers to me.
Let's cut the battery pack to a more realistic 60kW, ~960lb at $15,000 ([1] and [2]) from a Chevy Bolt.
Just to be stupid, lets add a pair of 100hp motors to it. For under $10K. Here's the first ones I ran across on Google: https://www.automationdirect.com/adc...TCP-100-3BD18C
Now according to your very generous numbers we could run our 11kW generator continuously and never drain the battery. We'd even have about 5 hours of runtime until we had to turn on the generator at all.
So now at WOT we've turned our cat into a powerboat, but we'll drain the battery in about 15 minutes. At least we know the battery is designed to deliver this kind of power (though to be honest, who knows for how long) since the Bolt has a 200hp/150kW motor.
So let's randomly use a 20kW Northern Lights generator, just because we can. No, this isn't going to let us run WOT appreciably longer, but it is going to let us cruise at this speed, using your numbers, indefinitely, and not need to run for about 8 hours a day to do it. That doesn't include the 10kW (using hopefully more realistic numbers) we got off solar that day. So we used about 27 gallons of diesel that day to do that. Hopefully we don't need to do that very often.
Because we're DIY fanatics, we've spent somewhere around $35K to put all this together (not including doubling the number of solar panels you might have otherwise had, or the incremental upgrade of the generator).
A system that will run for a few hours with no diesel at all, put 10kW into the batteries on a good day, let us run as much air-conditioning as we might want, be lower maintenance, and quieter, and a lot cheaper to service if and when something does go wrong. The battery isn't cheap, but if it lasts the 10 years GM thinks it will, you'll probably break even on fuel costs, and the replacement you buy will probably be significantly cheaper. And you didn't have to pay for a large house bank.
To me it makes a lot more sense to think of your cat's hybrid system as closer to a BMW i3 than a Nissan Leaf. You drive the BMW around town and 90% of the time you never need the range extender. It's there for when you want to push the range. That's the hybrid system to shoot for in a Cat. Most of the time, hopefully, you don't need more than a few hours of motoring. But when you do, you're covered. And if you really need more than 15kW of power, well, it's not like that's expensive. It's just not a commodity product you can buy off the shelf for a reasonable price for marine applications right now, for reasons that are probably obvious after reading this thread. But there's really no reason an electric motor should cost more than your average generator containing both an equivalently strong motor, and a diesel engine except for the fact that right now, nobody is buying them.
[1] How much is a replacement Chevy Bolt EV electric-car battery?
[2] https://www.gmpartsdirect.com/oem-pa...ttery-24286671
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05-10-2017, 19:51
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#50
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Registered User
Join Date: Nov 2014
Posts: 261
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by 44'cruisingcat
Claiming a 20 kw electric motor is EQUAL TO a 33kw diesel is misleading, dishonest, and potentially dangerous.
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20hp. 15kW. I think someone not as informed as yourself might read your comment and come away with the impression that we're talking about a doubling of boat speed with the larger engine, when you're actually making these dramatic claims about something more like a 20% difference in boat speed.
Which I don't think is very helpful. But you do you.
Quote:
So if you're prepared to seriously compromise your boat's capabilities, and pay a serious financial premium for doing so, then hybrids make perfect sense.
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Pricing on non-marine applications looks pretty reasonable to me. Torqeedo and Oceanvolt are charging more than twice what they might for their systems because the market just isn't there for the larger systems right now. You can buy a battery pack from BMW, or Torqeedo. The only difference is the Torqeedo version costs twice as much for the same battery pack and has a warranty for it's use (after you find an expensive certified installer I'm sure).
In the 2030 Lagoon 40, diesel will be an option, and it'll cost more than the higher battery capacity, lower TCO electric option. Almost no one will buy it.
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05-10-2017, 19:54
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#51
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Registered User
Join Date: Mar 2017
Posts: 293
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by ssmoot
Those seem like very reasonable if not overly generous (in favor of electric) numbers to me.
Let's cut the battery pack to a more realistic 60kW, ~960lb at $15,000 ([1] and [2]) from a Chevy Bolt.
Just to be stupid, lets add a pair of 100hp motors to it. For under $10K. Here's the first ones I ran across on Google: https://www.automationdirect.com/adc...TCP-100-3BD18C
To me it makes a lot more sense to think of your cat's hybrid system as closer to a BMW i3 than a Nissan Leaf. You drive the BMW around town and 90% of the time you never need the range extender. It's there for when you want to push the range. That's the hybrid system to shoot for in a Cat. Most of the time, hopefully, you don't need more than a few hours of motoring. But when you do, you're covered.
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Great info. I've always been a sailor who enjoys watching weather windows and rarely push through with motor unless I'm on a real timeline (all of my sailing is charter right now) so that's exactly how I'd use the system. One really attractive side benefit I hadn't thought of was running AC at night with no genny running. I don't need AC, but my parents are older and when they're on board, I like them to be comfortable. I'm guessing Moonwave has a soft-start, but even still, I'm curious about the electric system's brains to handle that kind of load.
For clarification, are you saying that an 11kw genny could put more juice into the system then a single electric motor would use under moderate load (say 6kts) thus allowing for continuous run until you ran out of diesel?
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05-10-2017, 20:04
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#52
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Registered User
Join Date: Nov 2014
Posts: 261
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by Thalas
For clarification, are you saying that an 11kw genny could put more juice into the system then a single electric motor would use under moderate load (say 6kts) thus allowing for continuous run until you ran out of diesel?
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Using Dave's numbers, yes.
In hindsight I think you'd probably want a bigger genny so you're not running it the entire time. It'll also be more fuel efficient (at least based on the Northern Lights 12kW at 1.2gph vs 20kW at 1.7gph estimates).
EDIT:
To get ahead of the obvious: This isn't as efficient as driving the boat directly with a diesel engine. But then that boat doesn't get to motor silently for any amount of time, doesn't generate power if the wind picks up for a couple hours, doesn't let you run air-conditioning at night without a generator also running, etc etc.
I do think, with "enough" solar, that you could afford to splurge on luxuries like air-conditioning occasionally, handle the rest of your hotel loads, including a water maker and washing machine, use your motors as much as you need for maneuvering and never have to fire up the generator at all. And I don't think such a boat is necessarily all that exotic. Manufacturers like Lagoon with the new 40 just need to stop making it difficult to install such arrays by including unnecessary flair in the salon tops (seriously; why does that "taco" shape need to be there?).
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05-10-2017, 20:16
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#53
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Registered User
Join Date: Dec 2014
Posts: 600
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by StuM
If I understand you correctly, you are saying that an electric motor on a boat is generally operated at very low RPM. Is that correct?
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yes, I think we ought be interested in slowing the screw down, therefore the motor would be designed to run at that RPM.
The thing is the system isnt tied to the same metrics anymore. You arent looking to match the peak torque (which is turning force) via the speeds of available transmissions at 2400 RPM that a diesel produces, because the power characteristics are different.
As hybrids, DE subs face the same issue, and they resolve it by having the diesels turn a generator which powers the electric motor usually just outside the casement where it has access to cooling water. Thats how they harmonise the difference in characteristics, and of course no gearbox as they can synthesise the shaft speed and direction electronically. They can even multiply torque at the shaft for 2x or 4x for short periods of time.
The generators have enormous output so that they have enough power to to both turn the motor and recharge the battery in a relatively short space of time, so that time exposed on the surface or at snorkel depth is kept to a minimum.
In our case the battery is fully one and a half decks of a 3 deck boat, made up of 2.2 volt lead acid cells as high as a man with around the same footprint.
__________________
'give what you get, then get gone'
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05-10-2017, 20:22
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#54
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Registered User
Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,987
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by Thalas
Moonwave is a hybrid cat. Here are her specs:
144V 23KWh Li-FePO4 battery bank
24V 4.8KWh Li-FePO4 battery bank
Fischer Panda 22 KW 144 DC generators (x2)
AC system runs from batteries at night – no generator noise
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I'm worried because I am out of my depth here and just getting deeper and deeper but I enjoy working on it, I might learn something. So value this information for what it costs you ...................
The engines on the Gunboat in your link are 2 x 18kw and the advertised boat weight is 16-19t
Interesting side note: - They believe it may at times need to carry 760liters of fuel (200US Gallons)
At 19t I think you would draw =/>18kw (again just a guess) for 6kn of speed. I couldn't find a manufacturers spec on this.
If that's close you should get a bit less than 8nm on the main battery bank at 6kn with no other assistance.
The generators are huge and can easily out supply the electric motors, enough to recharge the batteries as you go. One generator could run both motors at 9kw each or both generators for one hour on one hour off. Not counting solar intake.
Running the generators to run the electric motors isn't as efficient as running a fuel engine directly to the drive. Not sure how much you might loose in the conversions but significant.
Not sure how much power their air conditioner pulls but with the batteries full when you go to bed (4.8kw) it sounds marginal to me for 8 hours sleep, they may borrow from the other battery bank, if so then there is heaps.
P.S.
Another interesting point is with 2 fuel driven engines it is more economical to run just one when travelling because of the inefficiencies of torque and fuel consumption curves. Electric engines I suspect would be more efficient running both at once.
__________________
Regards
Dave
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05-10-2017, 20:35
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#55
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Registered User
Join Date: Dec 2014
Posts: 600
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by Dave_S
P.S.
Another interesting point is with 2 fuel driven engines it is more economical to run just one when travelling because of the inefficiencies of torque and fuel consumption curves. Electric engines I suspect would be more efficient running both at once.
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Im pretty sure one would be better. Cats can run just one screw and yet not wander around due to the asymetrics of the thrust. You might for instance have a large screw for cruising on and another on the other hull just as a manoeuvring force. Or two the same for the highest possible dash speed.
Whatever you do there though, the shut down motor has to have a feathering or collapsible prop to save the drag. Not having two of those is a tasty cost reduction if you are avoiding the 'Greenacres 'Money is no Object'' plan
__________________
'give what you get, then get gone'
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05-10-2017, 20:42
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#56
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Registered User
Join Date: Nov 2014
Posts: 261
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by ZULU40
Whatever you do there though, the shut down motor has to have a feathering or collapsible prop to save the drag.
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No no, you've got it all wrong. You put a bigger motor on the dragged (drug?) side and use it to generate all the power you need to charge your batteries and power the smaller drive motor.
(Don't shoot! )
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05-10-2017, 22:14
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#57
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Registered User
Join Date: Apr 2013
Posts: 11,002
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by ssmoot
Except you shouldn't be sizing a diesel for peak hp. It's inefficient and miserable.
No you typically size it at 70-80% of peak HP with a reserve left for emergency conditions.
You CAN size an electric system that way because you don't pay either of those taxes.
If you size an electric motor to run at 100% of peak HP doing 70% of hull speed in calm conditions. Even modest contrary conditions and you have significant performance loss.
You're buying the upgraded 57hp diesels in the Lagoon 42 for their 2,000RPM performance, not their 0.9kn faster 3,200RPM performance. At least that seems like a very reasonable argument to make to me.
"magical" is awfully condescending. Take marketing with a healthy dose of salt sure...
If they were saying you could downsize by 20% (40HP diesel is replaced with a 35hp electric), because you can run them at 100% of rated HP, I might buy the marketing fluff. It's wrong because it's about reserve power for emergency conditions but at least they would have a more defendable position. But they are claiming 50-80% reductions in HP are equivalent and that snake oils salesmanship and deserves condescension
, but even if you disagree and think most buyers buy an engine for it's WOT performance, I think there's at least a significant minority who are more concerned with balancing cruising speed and efficiency, and for them, comparing WOT between diesel and electric makes no sense at all, and comparing a lesser power electric motor (how much lesser may be up for debate) to a more powerful diesel makes a ton of sense since they totally can run the electric version at WOT without suffering horribly.
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Again, if you want to claim current cruising boats are overpowered, that's fine if you are willing to live with the loss of performance but that's not a diesel vs electric issue. To claim 15hp electric is equivalent to 45hp diesel is an outright lie.
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05-10-2017, 22:22
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#58
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Registered User
Join Date: Apr 2013
Posts: 11,002
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by ZULU40
this is because the expectations of power are completely different. We all have the image of the climbing somewhat parabolic torque curve for IC engines, what people might not be aware of is that electric motors start with max torque at the lowest operating RPM, and the same motor is calculated to produce max HP at highest RPM, where torque is a virtual zero. The important and useful curves are the inverse of one another.
Add to that, you wouldn't have an IC engine which you intended to run flat out all the time, the useful torque the engine is required to extract is a long way from zero RPM, but for electric motors this is closer to normal operation. And so the hypothetical 33hp engine will rarely see max power and much of its capacity is almost permanently wasted.
All that said, the success of hybrid cars has tilted views on the potential for boats, for cars succeed because they are in a driving patterns are largely variable power requirements. A car stopped at a traffic light requires less power than it produces, likewise going downhill it is commensurately less a power consumer than going up.
If electric boats are to succeed they will need to perform almost exclusively without engine assistance, because we must assume there is a constant power requirement with little variation. Certainly a reserve generator should be in the plan, but we ought be thinking the electric resources will cover 95% of the possibilities at a minimum.
I think we aren't there yet, but technological advances in solar generation and air independent engines appear to be such that, I am expecting that somewhere in the not to far distant future there will be boats with a 100% reliance on electric generation. It is simply a matter of time.
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I'm fully aware of the torque characteristics. As you indicated, they work wonderfully for a car in stop and go traffic as the hybrid smooths out the power demand on the engine.
But for a displacement cruising boat, that advantage goes away. Unless massively oversized, the diesel engine at cruise speed is typically running at a very efficient RPM/Load.
A pure electric sounds great and when the batteries can store enough power, they will end the days of internal combustion engines. Based on the development, I expect to be dead and gone for a long time before that happens. We aren't talking a 20% improvement in battery technology to reach a tipping point. It's a order of magnitude improvement that's needed.
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05-10-2017, 22:28
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#59
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Registered User
Join Date: Apr 2013
Posts: 11,002
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by ZULU40
Not true at all, any motor or engine loses 2% per bearing, trans included. For instance the 3 phase induction motor, where induction itself is a lossless transmission of electric power, is 96% efficient at best, because it requires 2 sets of bearings, one each end of the shaft.
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Diesel motors are typically rated at the crankshaft. There are some losses going thru the transmission to the driveshaft.
But your example of 96% efficient electric motors in a hybrid while technically true is misleading.
Example (exact percentage loss will vary based on the exact model. This is to demonstrate the concept):
- 50hp diesel: Loses 10% going thu transmission...result 45hp at the prop shaft.
- 50hp diesel powering a hybrid: Loses 6% converting to electric, Loses 10% converting to battery, loses 4% in the electric...result 40hp at the prop
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05-10-2017, 22:32
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#60
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Registered User
Join Date: Nov 2014
Posts: 261
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Re: Solar sails and the future of hybrid cats
Quote:
Originally Posted by valhalla360
I'm fully aware of the torque characteristics. As you indicated, they work wonderfully for a car in stop and go traffic as the hybrid smooths out the power demand on the engine.
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This certainly isn't true for a series hybrid or pure electric vehicle. What you're describing only applies to parallel hybrids. Which isn't what we're discussing when we're talking about a hybrid system on a boat. There's no mechanical coupling there.
At least in this discussion. Nanni mentions an inline motor similar to some "start/stop" hybrid systems in their brochure, but other than a marketing diagram, there's no specifications for it that I could find.
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