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Old 04-10-2017, 20:26   #1
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Solar sails and the future of hybrid cats

I'm not interested in why hybrid is a bad idea. I would love to have a conversation for those of us interested in possible hybrid cats to discuss the nuts and bolts challenges and benefits to such a system.

I've been reading more about solar sail fabric (especially the Arcona 380Z equipped with Powersails generating 1kw/hour) where "Modern thin-film photovoltaic cells do not need direct sunlight to generate electricity. In fact, the panels on the sail opposite the sun will generate 30-40 percent of their maximum output with the indirect and reflected light.

The 15kw Oceanvolt electric motor is equivalent to a 45hp Diesel motor and with an 11kw generator and 80 gallons of fuel, would have a range of 600 miles before any solar input was added to the battery bank. Current setups generally allow a battery bank to supply power for 4-10 hours at 4-6 knots. LiPo batteries will continue to drop in cost and significantly larger banks should be affordable in the near future.

Since most modern cats have no problem fitting 1kw of hard solar panels without cluttering the deck, assuming another 1kw of solar sail power in ideal conditions, what size bank could be filled on a sunny day and correspondingly, what ideal range might be expected based on these numbers?
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Old 04-10-2017, 22:17   #2
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Re: Solar sails and the future of hybrid cats

FYI, here's a picture of one of the sails with embedded solar.
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Old 05-10-2017, 03:57   #3
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Re: Solar sails and the future of hybrid cats

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The 15kw Oceanvolt electric motor is equivalent to a 45hp Diesel motor ?
I'm dissapointed. I thought one electric kilowatt was equal to at least a million diesel horsepower.

So, to the question the electric disciples never answer. If 15 electric kW can replace a 33kW diesel, why not use an electric motor to power the generator? You could easily run a 25kW generator with a 33 kw diesel, ( so therefore a 15 kw electric motor. ) So you'd get 10 kw free.
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Old 05-10-2017, 04:51   #4
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Re: Solar sails and the future of hybrid cats

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I'm not interested in why hybrid is a bad idea. I would love to have a conversation for those of us interested in possible hybrid cats to discuss the nuts and bolts challenges and benefits to such a system.
Could you define the difference for us?

If we aren't allowed to point out the problems and limitations of a hybrid, it's really hard to have a meaningful discussion and how to address those issues.

The first challenge I suggest researching is the definition of horsepower (or watts if you prefer). There is absolutely zero difference between gas, diesel, steam, electric or unicorn fart based HP.

There is a difference in the torque curves but it really doesn't impact the HP selection in a displacement cruising boat since they run at constant speed and it's easy to size them to operate at or near peak efficiency.

Yes, it's completely viable to build a hybrid powered boat but you need to define what problem you are solving before we can help you with the "nuts and bolts". For most normal cruising uses, there is nothing to gain from a straight up hybrid (like the original Prius). Hybrid in cars takes advantage of city driving patterns where you go from hard acceleration to hard braking every minute or two. The hybrid can smooth out the power demand for the engine allowing it to stay near it's peak efficiency.
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Old 05-10-2017, 04:55   #5
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Re: Solar sails and the future of hybrid cats

From a prior post on a similar topic I put this together:

Let's say you have a cat that would normally get a pair of 30hp diesels with a 10kw generator. Instead install a 45hp in one hull (not much more up front cost and not much difference in size) and a 10kw electric motor in the other hull with a 10kw generator and say a 5kwh (usable) battery bank.
- Maneuvering in tight spaces, other than learning to deal with slightly different motor response, it should maneuver just as well. It's pretty rare to ask for full power when docking anyway.
- If doing a longer run, many just run on one engine anyway so the 45hp should be fine. If you want to tweak for maximum efficiency, you can figure your travel time and set the electric motor based on that. Example: say it's a 2hr run, you can set the electric motor to put out 2kw and reserve 1kwh for manuvering when you get to port and use that to supplement the big diesel.
- If you are just out for a sunset cruise or sight seeing in residential canals 2-3kts may be quite acceptable. Run on the electric at 2kw and you have a 2 hr range with 1kwh reserved for docking.
- If you do get into bad conditions, the big motor and generator can supply the same total power as the original pair of 30hp motors for as long as the diesel holds out.
- If the big diesel dies, the generator can keep you moving as long as the diesel holds out.
- If both engines die, you still have 5kwh in the batteries as a short term backup. (also you have at least some instant power say if your anchor starts dragging)
- A 10kw generator is not massively oversized like a full blown hybrid would be for house loads but plenty for the helper electric drive.
- Assuming the 5kwh bank can be accessed by the house loads, at anchor you can probably cool the boat in the evening with the generator and use battery power to run the air/con for the rest of the night. Say a 12k btu drawing 1.5kw at 40% duty cycle will run a little over 8hrs on batteries. That will keep things quiet in the anchorage at night.
- Assuming you put a 1000w of solar panels on the boat (it's a cat with more space) and an average of 5hr of rated output per day, that will top up the battery bank most days and or supplement if you are cruising during the day allowing you to put more load on the electric motor.

Overall shouldn't cost much more than a standard cat with a generator as the 30hp diesel is replaced by an electric motor and an upsize in the battery bank size. The cost of a 30 vs 45hp motor isn't that much. At the same time, if you are intent on efficiency and willing to downgrade performance, you can get a significant percentage of your power from solar/shorepower/battery but if you want performance, you can easily power up the big diesel and see no loss in performance.

I'd have to do detailed calculations to see if it makes financial sense but if a manufacturer wanted to go after the "eco" market but still have a fully functional boat, for a customer base willing to pay more regardless of if it makes sense, it should work.
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Old 05-10-2017, 05:50   #6
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Re: Solar sails and the future of hybrid cats

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So, to the question the electric disciples never answer. If 15 electric kW can replace a 33kW diesel, why not use an electric motor to power the generator?
You are the one making mistakes now.

The diesel can _never_ generate 33kW in electrical power. The hp from the engine is not calculated from how much electrical power it can generate.

The 15kW electric motor can take this power for years. It can also take 30kW for a few minutes, or even 45kW for a few seconds.

Mostly the people with 45hp engine run them at a much lower rpm, and therefore not at 45hp all the time anyway.

In this sense, the two are "equal" as they can both push the boat at 6 knots or whatever, for extended periods, and both have power to move quickly in bursts.

The electric
  • will still outperform the diesel in short bursts
  • can charge from solar, and tow generator.
  • is more quiet and reliable.
  • Less maintanence.
  • Won't make you sick from fumes

This being said, I got rid of electric power for practical reasons. It still makes a hum noise, and it's makes you lazy. I found the sculling oar is a true solution offering speed of 2 knots plus current. It makes you more fit and strong so you can live long. So, electric is dumb, and so are propellers.
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Old 05-10-2017, 05:58   #7
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Re: Solar sails and the future of hybrid cats

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You are the one making mistakes now.

The diesel can _never_ generate 33kW in electrical power. The hp from the engine is not calculated from how much electrical power it can generate.
That might be why he said a 33kw diesel could power a 25kw generator.

But his point still stands, if a 15kw electric motor is equivilent to a 33kw diesel, why not just connect the 15kw eletric motor to the 25kw generator. You could feed 15kw from the generator back to the electric motor and use the remaining 10kw to use for what ever purpose you like.

He wasn't making a mistake. He was pointing out the flaw in the dishonest distributors claiming magical electric HP.

Now if you are willing to limit a boat with say an 8kt hull speed to 6kts, you can get away with lower electric HP in calm conditions...but you can also get away with lower diesel HP in calm conditions. You are just accepting lower performance requirements. Nothing magical about electric HP.
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Old 05-10-2017, 07:58   #8
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Re: Solar sails and the future of hybrid cats

I don't understand why these threads always devolve into comparing hp.

You'd choose a 15kW motor because you need to size components for the motor, and you've decided that speed at "WOT" isn't the deciding factor for you.

Is it any surprise that the incremental cost in going with bigger diesels, where you don't have to resize every other component encourages you to up-size the engine?

In normal conditions, a smaller motor does the job cheaply and efficiently, and both of those things are going to be a high priority for most people considering a re-power electric conversion I imagine.

High horsepower (33kW and up) 3-phase motors are dirt cheap. You could buy a dozen of them for the price of a single diesel. Not from Oceanvolt or Torqeedo, but you could afford to replace the motor every couple years and end out ahead of their prices. If you were buying a boat from a manufacturer, and they offered you a choice between 15kW and 33kW systems for an incremental cost, then sure, you might be seeing larger systems discussed more frequently.

The much more interesting conversation IN MY OPINION, is battery banks, range/speed/power graphs, total system weight (motors, battery, generator, fuel, solar, wiring, controllers, inverters, etc) vs diesel (engines, batteries, generator, fuel, solar, wiring, controllers, inverters, pumps, wet-weight, misc electronics, etc) and total cost of both systems.

Electric will obviously be the economical, lower maintenance, more livable (NVH and house power) commercial solution eventually. Is that today? 5 years? 10 years? What about DIY? Just how cheap can you get a battery bank for? Commercial prices seem to be getting close to 2.5W/$ for the LifePO4 setups I've seen from US distributors.

Just off the top of my head, I think my own numbers would look something like: 24kW of batteries. Dual 15kW motors. 11kW generator. At least 2kW of solar minimum. Though I really like boats like the Nautitech Open 40 because of the opportunity for oversized solar setups.

So you'd get to motor around at somewhere around half-throttle indefinitely effectively. And if you only need it for a few hours, you might never need to turn on the generator. Is ~2 hours of continuous runtime at 30kW of max power enough? If you can figure out what the answer to that question is for you, you're a lot closer to figuring out if any of it makes sense for you.

How much are you spending in fuel costs today? Are you more risk tolerant? Satisfied you aren't seeing EVs catch fire all over the place? Don't think your boat offers a lot of opportunities for catastrophic cell punctures that somehow don't also involve getting run over by a container ship? You might be able to pick up an EV battery pack every 5 years in what you save on fuel. Every generation getting lighter, safer and more energy dense. Today that 24kW Nissan Leaf battery pack costs you $5K. The 60kW actively cooled Chevy Bolt pack costs around $15K at retail and weighs ~50% more at 960lbs. How does 3 hours at WOT and "unlimited" house battery with no generator running sound? It's still half the price of a 22kW BMW i3 pack from Torqeedo (you can buy that same pack used from eBay for under $6K).

A DIY system under $15K total? Maybe? Or are you holding out for twin 33kW motors and dual 100kW packs? Maybe that's your definition of viable. At what price does that start to look feasible to you for lower maintenance, fuel costs, decreased NVH and increased independence? Does the total weight of such a system (somewhere around 2,400lbs just for batteries!) make it a non-starter at that point and we'd have to see new battery chemistries to get off the fence?

I'd love to see Fuel Cell technology take over some day. So your city car can be a battery powered EV, but your primary road-trip vehicle can be fuel cell based and you don't have to worry about range or long breaks at charging stations. Maybe we'd see the first Container Ship that doesn't run on bunker fuel in a couple decades. But for sailboats, I think the weight penalty of batteries is more than made up for their efficiency, and with solar and continued improvements in chemistries, I expect there's an expiration date on diesel power in the next decade or two (hopefully).

That's just my 20c.
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Old 05-10-2017, 08:14   #9
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Re: Solar sails and the future of hybrid cats

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I don't understand why these threads always devolve into comparing hp.
I think it's because the electric motor vendors keep telling the lie that electric HP is magically more powerful than diesel HP. If you are going to say a 15kW electric motor is equivalent to a 33kW diesel, that's wrong from the start.

If you only need 15kW, you need to compare to a 15 kW Electric to a 15kW diesel.

If you want to talk about the torque advantage at low RPM, we can talk about that but nothing magical about electric HP.
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Old 05-10-2017, 09:14   #10
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Re: Solar sails and the future of hybrid cats

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I think it's because the electric motor vendors keep telling the lie that electric HP is magically more powerful than diesel HP. If you are going to say a 15kW electric motor is equivalent to a 33kW diesel, that's wrong from the start.

If you only need 15kW, you need to compare to a 15 kW Electric to a 15kW diesel.

If you want to talk about the torque advantage at low RPM, we can talk about that but nothing magical about electric HP.
Except you shouldn't be sizing a diesel for peak hp. It's inefficient and miserable.

You CAN size an electric system that way because you don't pay either of those taxes.

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, 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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Old 05-10-2017, 09:24   #11
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Re: Solar sails and the future of hybrid cats

It seems futile to engage in this debate with the OP until, and unless, he tells us - PRECISELY - why he has faith in the truth of the assertion he has borrowed from somewhere, presumably from the purveyors of the "Oceanvolt" motor.

The assertion, as you will recall, is: "The 15kw Oceanvolt electric motor is equivalent to a 45hp Diesel motor"

What - precisely - does "equivalent" mean in this context?

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Old 05-10-2017, 09:30   #12
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Re: Solar sails and the future of hybrid cats

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I think it's because the electric motor vendors keep telling the lie that electric HP is magically more powerful than diesel HP. If you are going to say a 15kW electric motor is equivalent to a 33kW diesel, that's wrong from the start.

If you only need 15kW, you need to compare to a 15 kW Electric to a 15kW diesel.

If you want to talk about the torque advantage at low RPM, we can talk about that but nothing magical about electric HP.
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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Old 05-10-2017, 09:59   #13
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Re: Solar sails and the future of hybrid cats

You are saying you can't get 45 usable hp out of a 45 hp rated diesel, but you can get 11 usable kw out of an 11 kw rated genset. Wishful thinking.
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Old 05-10-2017, 10:14   #14
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Re: Solar sails and the future of hybrid cats

As with most energy calculations, you have to decide what you are trying to achieve.

Regardless of size, a diesel generator driving an electric motor coupled to a a propeller shaft will always use more diesel fuel (and generate more CO2) to drive the boat at a given speed than a diesel engine coupled through a transmission to the same propeller shaft.

That's because substantial energy is used converting the rotational energy of the generator into electricity of the correct voltage and amperage, transmitting the electricity over wires and then converting it back into rotational energy at the correct RPM to drive the shaft. You lose at each conversion.

In the conventional diesel system the only loss is in the transmission between the engine and the shaft which is close to zero.

Fuel efficiency goes down if a diesel is not run in its efficient 25%-75% RPM range but that's the norm for sailboats (unlike cars or trucks)

Obviously, an electric motor can use electricity from other sources such as solar but on most sailboats it's only feasible to generate "hotel load" electricity from solar or maybe to get in and out of the harbor. There's not nearly enough panel space for long distance motive power even with solar sails.

If your goal is to save money, you might save by replacing one propulsion motor with a generator that you were going to buy anyways for use at anchor. While you would spend a bit more for diesel when using it to drive the boat, you can buy a lot of diesel for the cost of an engine and its maintenance. But I think a better idea would be to install enough solar and battery to not need a genset - pretty easy if you cruise where you don't need to run A/C.
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Old 05-10-2017, 10:30   #15
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Re: Solar sails and the future of hybrid cats

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As with most energy calculations, you have to decide what you are trying to achieve.

Regardless of size, a diesel generator driving an electric motor coupled to a a propeller shaft will always use more diesel fuel (and generate more CO2) to drive the boat at a given speed than a diesel engine coupled through a transmission to the same propeller shaft.
True

Quote:
Originally Posted by CarlF
That's because substantial energy is used converting the rotational energy of the generator into electricity of the correct voltage and amperage, transmitting the electricity over wires and then converting it back into rotational energy at the correct RPM to drive the shaft. You lose at each conversion.

In the conventional diesel system the only loss is in the transmission between the engine and the shaft which is close to zero.
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.

Strictly speaking a properly designed electric drive would run off a chopper controller and not require a gearbox. Car manufacturers are moving toward wheel motors for this reason.

Quote:
Originally Posted by CarlF
Fuel efficiency goes down if a diesel is not run in its efficient 25%-75% RPM range but that's the norm for sailboats (unlike cars or trucks)

Obviously, an electric motor can use electricity from other sources such as solar but on most sailboats it's only feasible to generate "hotel load" electricity from solar or maybe to get in and out of the harbor. There's not nearly enough panel space for long distance motive power even with solar sails.
and I think this is where it will go, the intersect of power generation that is edging up, and power requirements that are edging down.

For cats in particular a greatly reduced power requirement utilising narrow displacement hulls. Where for example cats in the low 30ft WL length would be requiring of 6HP to run at hull speed, very close to 8 knots. We are getting quite close to parity there, and the tech will be improving over time.
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