How feasible is 100% renewable electric cruising right now?

[GrowleyMonster]

Originally Posted by StuM

From a slightly different angle:

5kWh = 6.7 HP hr.

Common rules of thumb for diesel are: 1 gal per 20HP per hour or 0.05 gal per HP per hour.

So 5kWh equates roughly to 1/3 gal of diesel.

In the US, that would be 60c (5kWh @ 12c) v 83c (1/3 gal @ $2.50)


Of course, it depends on where you are and the relative prices of electricity and diesel.

Here, the diesel would be considerably cheaper than the electricity.
PGK5.15 ($1.62) for 5 kWh v PGK3.50 ($1.10) for 1.25 litres.

(and that's without taking Peukert into account, which means that we actually need more than 5kWh to replace 5kWh in the batteries)

Ummm, no not necessarily. Peukert is only a penalty when you are discharging at greater than C/20. For a battery rated at the 20 hour discharge rate, which is most batteries. At less than C/20 discharge rate, Peukert is actually a bonus and not a penalty. So if I am running at less than 11A on my 220AH bank, I get a little extra from Mr. Peukert. If I run at greater than 11A then Peukert takes his slice. I actually track my usage and factor in Peukert so I don't accidentally go deeper than 50% actual SOC. I know I can get away with going deeper a few times but hey, I save that for emergencies. Batteries are over 3 years old and holding up nicely so it must be working okay.

Also, calculations aside, I know from experience that I can't stay out all day motoring on 1/3 gallon of gasoline fed into an Atomic 4, which I used to have. Or a 4HP Nissan outboard, which I also used to have. Sometimes the practical is different than the theoretical.

[StuM]

Originally Posted by GrowleyMonster

Ummm, no not necessarily. Peukert is only a penalty when you are discharging at greater than C/20.

You are correct. I was wrong to use "Peukert" as shorthand for "charging efficiency".
I was referring to the fact that 1kWh delivered to a battery during charging does not equate to 1kWh of energy stored.

Also, calculations aside, I know from experience that I can't stay out all day motoring on 1/3 gallon of gasoline fed into an Atomic 4, which I used to have. Or a 4HP Nissan outboard, which I also used to have. Sometimes the practical is different than the theoretical.

But can you "stay out all day motoring" at the same speed as you did with the Atomic 4 or Nissan outboard on 5Wh of battery usage?

Also: petrol/gas or diesel. Valhalla illustrated the petrol/gas v electricity situation. I illustrated, as I said "from a slightly different angle" , the diesel v electricity situation

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[GrowleyMonster]

Originally Posted by StuM

You are correct. I was wrong to use "Peukert" as shorthand for "charging efficiency".
I was referring to the fact that 1kWh delivered to a battery during charging does not equate to 1kWh of energy stored.



But can you "stay out all day motoring" at the same speed as you did with the Atomic 4 or Nissan outboard on 5Wh of battery usage?

Also: petrol/gas or diesel. Valhalla illustrated the petrol/gas v electricity situation. I illustrated, as I said "from a slightly different angle" , the diesel v electricity situation

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I never have cared about speed, so I always poke along. I am on the boat, therefore I am already at my destination. But for the same ground covered, the electric has either one beat on the fuel consumption. If you mean as fast as most people go, which is wide open throttle, no I certainly can't match the range at speed. Never said that. With electric, even with onboard solar charging and lots of it, you have to give up something. Usually, it is speed. Sometimes it is range. Sometimes just a little of both. But if I go out for a day of fishing, I have a good time for less than a bucks worth of juice. Never was able to do that with pistons and pushrods.

Charging efficiency is pretty high through the bulk stage, and into the absorption stage. By the end of the absorption stage efficiency is dropping off, and at full float stage, efficiency is well, zero. But current is only an amp or two, at float, and you could of course not top up the batteries at every single charge cycle. When I am home I never leave them on float.

[valhalla360]

Common issue when comparing ICE to Electric is the proponents size and operate the electric at much lower power and speeds and then point at the great efficiency.

A motor designed to comfortably run the boat at 80-90% of hull speed with the capability to run at 100% for hours or even days is not he same motor you would spec to run at 30% of hull speed.

Your 48v at 11amps translates to about 2/3hp output. Idle speed on a 15hp diesel is likely more than 2/3hp.

Had a 50cc moped as a kid (about 2.5hp) and the 1/2 gal tank was enough to mess around all day. I expect if you hooked up a 4stroke 50cc engine to the right gearing and ran it at 2/3hp output, it would get you some pretty darn good efficiency if you only want 3kts on a 27' boat in calm conditions. It's just that no one has bothered to take the time and effort to do this and really dial it in for efficiency because your average 27' sailboat with a 10-15hp diesel is already plenty efficient for most.

Electric is easy to downsize the power especially when it's hard to supply power to a big HP electric motor anyway.

[GrowleyMonster]

Originally Posted by valhalla360

Common issue when comparing ICE to Electric is the proponents size and operate the electric at much lower power and speeds and then point at the great efficiency.

A motor designed to comfortably run the boat at 80-90% of hull speed with the capability to run at 100% for hours or even days is not he same motor you would spec to run at 30% of hull speed.

Your 48v at 11amps translates to about 2/3hp output. Idle speed on a 15hp diesel is likely more than 2/3hp.

Had a 50cc moped as a kid (about 2.5hp) and the 1/2 gal tank was enough to mess around all day. I expect if you hooked up a 4stroke 50cc engine to the right gearing and ran it at 2/3hp output, it would get you some pretty darn good efficiency if you only want 3kts on a 27' boat in calm conditions. It's just that no one has bothered to take the time and effort to do this and really dial it in for efficiency because your average 27' sailboat with a 10-15hp diesel is already plenty efficient for most.

Electric is easy to downsize the power especially when it's hard to supply power to a big HP electric motor anyway.

Exactly. A 30HP or 15HP or whatever gas or diesel engine has a minimum idle speed and no choice of gear ratio. You are basically stuck running 5kt or whatever, minimum. And the overhead from simply running the engine doesn't go away until you kill it. Most electric installations are out of necessity power smart setups. Sort of like an infernal combustion installation should be but isn't. Well, maybe not "should be", since by the nature of the beast a wasteful excess of power is actually needed at times, and so most boats are a bit overpowered. With electric you can feel free to install a bigger than needed motor, because there is very little penalty in doing so. For instance, I have ran a 5kw motor and a 12kw motor. When I run both at 1kw power, they both turn over at about the same speed for the same power consumption. Or more to the point, for a given prop speed, both motors require the same power input. The only real difference is top end performance. A 10hp diesel turning at 700 RPM and a 30HP diesel turning over at 700RPM do not have the same fuel consumption.

When you are talking about efficiency you are talking about soething that e-boaters obsess over. We have to make so many compromises that first of all we learn to live with them, and second we learn to optimize. Not for reasons of economy, but for reasons of performance and utility. That's not to say that some of us aren't happy to be saving money, mind you, but it is secondary to actually making technology that has room for improvement, to work. And there is the rub. Boat people usually do not obsess greatly over efficiency since a tank of fuel is peanuts compared to other associated expenses. So the buyers like a lot of power, and the builders have little choice but to listen if they want to sell boats. From an engineering standpoint it is just silly to exceed about 2/3 theoretical hull speed on a displacement hull. But owners like to dig a hole in the water and attempt to climb their boat up out of it. Me, when I look over my stern and see no sign of my passing in the surface of the water, I am happy, because I know that my hull is presenting the minimum load to the plant driving it. The guy with the brand new Benny that likes to rock me awake at 1000 every Sunday morning obviously enjoys pulling water behind him and pushing up an immense bow wave, and he is not alone. Good engineering has to start with the owner/buyer/operator.

[CatNewBee]

Yeah, this are all the greenish statements I hear over and over. Eat veggies, drive a bicycle, lower speed limits to lower fuel consumption, make compromises, use public transportation... bla.

When it comes to heavy weather on a lee coast and there is no power in your engines to fight the storm, you'll end up properly grounded. Even if your electric motors do have enough power, your batteries probably will not stand.

For all easy cruising when the sun shines, it might be great, but if you are in trouble, you'll need any HP you can get as long as it takes. Diesel has a much higher energy concentration per kg than any battery can provide today.

BTW, on a sail boat you use the engine only occasionally, so it does not matter at all how much fuel it consumes when idling.

[valhalla360]

Originally Posted by GrowleyMonster

Exactly...

I appreciate your comments unlike some of the proponents who refuse to admit the downsides, you give a balanced view which is much more useful for someone considering motor choices.

We may disagree if a 30hp motor on a 35' boat is or is not overpowered but at least you don't claim a 3hp electric motor is equivalent to a 30hp motor.

I can see some viable mainstream electric drive uses:
- Dingy if you primarily use it to go under 1/2 mile to shore once or twice a day. Just need to work out a charging system whether that be a small array mounted on the dingy or a lead ran from the mother ship. This is a very viable option. With narrow catamaran hulls, you could probably get a decent turn of speed for very little power. Maybe a hull design with a knuckle so when running light, it's very slippery but if you need to haul water/fuel, it has some load carrying capability.

I do think a Non-100% option is viable for a catamaran. 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.

[GrowleyMonster]

Originally Posted by CatNewBee

Yeah, this are all the greenish statements I hear over and over. Eat veggies, drive a bicycle, lower speed limits to lower fuel consumption, make compromises, use public transportation... bla.

When it comes to heavy weather on a lee coast and there is no power in your engines to fight the storm, you'll end up properly grounded. Even if your electric motors do have enough power, your batteries probably will not stand.

For all easy cruising when the sun shines, it might be great, but if you are in trouble, you'll need any HP you can get as long as it takes. Diesel has a much higher energy concentration per kg than any battery can provide today.

BTW, on a sail boat you use the engine only occasionally, so it does not matter at all how much fuel it consumes when idling.

Valid points, yes. However just to clarify, I am not all about green issues. I just like quiet, non smelly propulsion, avoiding big fines for spilling fuel, reliable, instant start and torque, no trips to the fuel dock, equipment cost, and other issues. It is a good fit for me. Maybe not for you. As for the lee shores, well, clearly they are not good places to be. So the obvious solution to that, is to treat them the way sailors treated them before auxillaries became common, which is to say, watch the weather and stay away from them.

The fact that a proper sailboat properly sailed doesn't need to motor except when docking etc, is actually a good thing for electric, because you can get by with a smaller bank if that's your style. This is always the big sticking point with electric: the size, weight, and cost of a bank big enough to do the job. Four group 31s is not much more battery than the average house bank. Eight L-16s is getting into some serious weight and space, and going with Lithium or other advanced technologies costs a bundle. Then again, a big propulsion bank quickly becomes a valued resource and especially for a liveaboard, one you will wonder how you ever got along without.

[john61ct]

Safety and redundancy is just one design factor, simply make that a high level priority in the overall hybrid systems design.

I'd spec a pair of largish diesel gensets, able to deliver sufficient power realtime for emergency conditions, to a pair of powerful EV propulsion drivetrains.

The large LFP battery bank stores energy to allow timeshifting between generation and consumption, also taking advantage of a large solar array for normal living on the hook and fair-weather short-term motoring conditions.
Enough solar and conservation measures, maybe the gensets are rarely used. But they are there when needed.

[valhalla360]

Originally Posted by john61ct

Safety and redundancy is just one design factor, simply make that a high level priority in the overall hybrid systems design.

I'd spec a pair of largish diesel gensets, able to deliver sufficient power realtime for emergency conditions, to a pair of powerful EV propulsion drivetrains.

The large LFP battery bank stores energy to allow timeshifting between generation and consumption, also taking advantage of a large solar array for normal living on the hook and fair-weather short-term motoring conditions.
Enough solar and conservation measures, maybe the gensets are rarely used. But they are there when needed.

Problem with 2 large gensets and 2 large electric motors is they are inefficient, heavy and big. A 20kw genset is much larger and heavier than a 20kw propulsion motor plus the energy conversions make it less efficient than just connecting the motor to the propshaft. Plus the gensets are over sized for house loads again making them inefficient and prone to carboning up if used mostly as generators.

Much more efficient to just go with a pair of standard diesel propulsion engines and a genset sized for house loads.

Example: Northern Lights 20kw generator = 820lbs
Yanmar 25hp diesel (slightly less than 20kw) = 396lbs.

Yes, you have to add a transmission to the Yanmar but that should balance out against adding the electric motor to the hybrid system. If you add a propulsion battery bank, it can quickly add a few hundred pounds more and you need to find more space. On a small boat particularly if it's weight sensitive design, that's a lot of weight and space to find.

[john61ct]

Originally Posted by valhalla360

Much more efficient to just go with a pair of standard diesel propulsion engines and a genset sized for house loads.
...
On a small boat particularly if it's weight sensitive design, that's a lot of weight and space to find.

The core topic is electric propulsion.
My post was addressing safety issues via redundancy.
Efficiency and weight are certainly issues, but since there are many such boats being built out there, it seems at least some feel the tradeoff worth working on.
Yes a huge LFP bank weighs more than long-range tanks full of fuel, but if the goal of solar taking the lions share is achieved, that can be reduced.

[valhalla360]

Originally Posted by john61ct

The core topic is electric propulsion.
My post was addressing safety issues via redundancy.
Efficiency and weight are certainly issues, but since there are many such boats being built out there, it seems at least some feel the tradeoff worth working on.
Yes a huge LFP bank weighs more than long-range tanks full of fuel, but if the goal of solar taking the lions share is achieved, that can be reduced.

The core topic is if renewable electric is viable. Once you add any generator, you are no longer on the core topic. That's fine. These threads often have a bit of drift and make interesting discussion but once we start adding diesel (direct propulsion or generator) it's no longer 100% renewable.

If you want to address safety, standard diesel propulsion properly maintained is better as there are fewer systems in the drivetrain to fail and they are well vetted and reliable.

If you want to go into some sort of hybrid system, see my prior post with a hybrid suggestion. It should be more reliable as there are fewer parts and it should have better efficiency and utilizes the systems more closely to their design intent. While it won't hit 100% renewable in the overall use scheme, it could probably hit 60-80% renewable for an owner willing to live with the limitations of renewable while still having a boat that could be sold to a typical cruiser as it doesn't sacrifice performance.

[CatNewBee]

Well - you know what - the whole hype about RENEWABLE is so stupid anyway.

Diesel / Oil / Gas / Coal IS renewable energy, it's organic, created by dead flora and fauna -it just takes very long until the CO2 cycle completes. It IS stored SOLAR power - not in lithium, but in organic chemistry created by photosynthesis in the first place.

We just help the process cycling by burning fossil fuel to help the plants get CO2 as food for their photosynthesis nowadays. The green house effect and the warming are good for the plants to grow. Also the highest biodiversity was in warm periods on earth, the ice-ages extinct most of the life, not the warm periods.



Ever heard from the first law of thermodynamics? Energy never can get lost - it is transforming in another energy type by increasing the entropy.

Burning wood to create steam for a steam engine is a renewable propulsion too. It's not just solar panels and wind generators. It does not matter how the energy is stored and recovered.

BTW even nuclear power is solar power. Uranium and all the heavy elements stem from a supernova / sun. It is stored solar power too. ;-)

[KTP]

If you could use the power pack from a modern electric vehicle, something around 60kwh and 2000 pounds (replace some of the ballast in a sailboat with the battery pack would be ideal).

A sailboat that might have a 25hp diesel probably only really uses about 5hp when puttering along at 1/2 gallon per hour and 5 knots.

So if the electric motor is 75% efficient, you might have around 5kW being drawn from the battery bank, giving you about 12 hours cruising at 5 knots. This would be equivalent to using about 6 gallons of diesel fuel.

This seems somewhat within reason since a 60kwh battery can drive a car at a 150 to 200 mile range, which would normally take about 6 gallons of gasoline (getting 30mpg).

If you could plug into 50 amp service, you could maybe recharge overnight.

For solar, 2kW of panels would take you about 5 days to recharge. So spend a lot of time at your anchor :-)

If you cruise at 3 knots, in calm water, you probably only need about 1hp and could probably go 60 hours or 180 nautical miles on a charge, with the 60kwh battery pack.

[valhalla360]

Originally Posted by KTP

If you could use the power pack from a modern electric vehicle, something around 60kwh and 2000 pounds (replace some of the ballast in a sailboat with the battery pack would be ideal).

A sailboat that might have a 25hp diesel probably only really uses about 5hp when puttering along at 1/2 gallon per hour and 5 knots.

So if the electric motor is 75% efficient, you might have around 5kW being drawn from the battery bank, giving you about 12 hours cruising at 5 knots. This would be equivalent to using about 6 gallons of diesel fuel.

This seems somewhat within reason since a 60kwh battery can drive a car at a 150 to 200 mile range, which would normally take about 6 gallons of gasoline (getting 30mpg).

If you could plug into 50 amp service, you could maybe recharge overnight.

For solar, 2kW of panels would take you about 5 days to recharge. So spend a lot of time at your anchor :-)

If you cruise at 3 knots, in calm water, you probably only need about 1hp and could probably go 60 hours or 180 nautical miles on a charge, with the 60kwh battery pack.

If you are willing to give up speed, range and convenience, it's viable today but you are being a bit optimistic.

On our Gemini (34' catamaran) we had a secondary motor mount that would take the 5hp dingy motor. Playing around dead calm flat water, It topped out around 2.5-3.0kts. A dedicated inboard setup might get you an extra knot due to a more suitable prop but 5kts...not likely.

On a smaller boat, power goes down but you also start running up against hull speed sooner. It also makes 1000lbs of batteries & 2kw of solar tricky to install and the economics start to struggle as these are fairly inexpensive boats where a $1500 outboard is what you are competing with.

If 3kts is an acceptable cruise speed and you cruise on small protected waterways where you are unlikely to need more power for more than a 1/2 hr or so, it's very viable.