Viability of electric only propulsion in 2018 - is there a good option after all?

[GrowleyMonster]

Originally Posted by john61ct

Perhaps you thought the above meant I think liveaboard cruising requires fossil fuels.

Not at all.

But EP used for liveaboard cruising on the ocean cannot replace fossil fuels, it only increases their usage through its inefficiency in requiring hybrid in order to be practical.

Depends on whether or not the diesel generator is the only means you have of charging batteries or not. If your system loses 30% efficiency due to using a generator, but gains 40% of its charge from solar and regen, then you have a net fuel saving. Just as an example. Depends a lot on how much you motor. If 1000w of solar is enough to get your bank charged up again before you need the prop, and you have 1000w of solar, then you don't need the generator at all.


One of the biggest advantages of EP is the ability to harvest free energy and use that, instead of diesel, for all or part of your energy needs. You can't harvest free diesel at sea.

[KTP]

Originally Posted by GrowleyMonster

One of the biggest advantages of EP is the ability to harvest free energy and use that, instead of diesel, for all or part of your energy needs. You can't harvest free diesel at sea.

It is also really hard to get contaminated solar energy.

[skipmac]

Originally Posted by KTP

It is also really hard to get contaminated solar energy.

This is not exactly an overwhelming argument for switching to solar. In forty years I picked up a load of bad diesel one time.

[Jim Cate]

Originally Posted by KTP

It is also really hard to get contaminated solar energy.

But not at all hard to get "contaminated" solar input... as in cloudy skies. And such will abort EP in much the same way that bad diesel fuel aborts fossil fuel propulsion.

Jim

[BigBeakie]

But if its cloudy and the wind is blowing, you could be harvesting significant regen battery storage if you get the right EP.


Sent from my iPad using Cruisers Sailing Forum

[DotDun]

Originally Posted by BigBeakie

But if its cloudy and the wind is blowing, you could be harvesting significant regen battery storage if you get the right EP.


Sent from my iPad using Cruisers Sailing Forum

That's the problem with EP, too many ifs......if you have a strict itinerary and can't wait for wind, EP via genset doesn't make financial sense, neither capex or opex.

[StuM]

Originally Posted by BigBeakie

But if its cloudy and the wind is blowing, you could be harvesting significant regen battery storage if you get the right EP.


Sent from my iPad using Cruisers Sailing Forum

Not when you're anchored.

[GrowleyMonster]

Originally Posted by BigBeakie

But if its cloudy and the wind is blowing, you could be harvesting significant regen battery storage if you get the right EP.


Sent from my iPad using Cruisers Sailing Forum

AND if you have the right speed through the water. At a steady 10kts you would maybe fully charge your bank in just a few days with regen. At 4kts under sail, with a 5kw motor I managed to get 140 watts, as I recall. That's about two lightbulbs worth of juice. Filling my 10.56 kwhr bank would have taken an awfully long time. Like forever. You can only harvest just so much energy from the prop for a given amount of water passing over it and a given amount of drag in the water. The motor and controller have very little to do with it. You could perhaps optimize the reduction ratio for regen and get a bit more, but then it would not be optimized for propulsion. Basically, for a small boat, regen is NOT significant and you are better off setting the throttle to zero energy consumed/produced, and getting your charge from solar panels once you have used up your shore power charge. In fact, if your bank is full, no reason not to use up all excess available solar energy production turning the prop, increasing your speed a bit. For a big boat, then yes, it can be said that regen has significant potential, because the bigger boat is more likely to hit double digit speed under ideal conditions. My little boat I am pretty sure has never seen over 6kts.


Then again, you haven't defined "significant" in this context. If you mean enough to burn LED running lights all night and keep your smartphone awake running OCPN, then sure, that is easy enough. If you think that sailing at 3kts for 6 hours will fully recharge a bank that you used to motor at 3kts for 6 hours, ain't gonna happen. Better figure on about 60 hours of regen at a given speed to repay the bank for those 6 hours motoring. And that might be a bit on the optimistic side, I don't know. All I KNOW is what my results were. I don't KNOW anything from reading glossy brochures and the glowing claims and handpicked fanboy reviews therein that I really don't regard as data. That wouldn't be impartial testing or critical reading. Don't drink THAT koolaid.



The best way to actually know how much charge you can get from the trailing prop is to actually sail an electric boat and do your own testing, as I did. I would love to see some real world regen test results from a big boat with a big prop running in the double digits, and the speed increase from then resetting the throttle to neutral power level. Boat owned and skippered, and data recorded, by a member here who does not sell EP components or systems, naturally.



I am not "anti-regen" but I know what I got with my boat and it didn't impress me very much. Not that I expected it to. Extended cruising with EP, with significant amount of motoring, requires a nice big solar array or a generator or better yet, both. Regen is just a small lagniappe, not a dealmaker.



One good thing about regen, though. If you are making the speed, you are getting it day and night, rain or shine. In some areas or parts of the year, weather conditions or daylight duration severely limits solar charging.

[KTP]

I wonder if sizing the prop quite differently for best efficiency regen you would be able to get quite a bit more, while still remaining efficient for sailing and motoring. It would seem that for regen you want a quite large prop and a big reduction drive to your motor (3:1, maybe 4:1)? so that the slow speed of 5 knots produces quite a bit of power. I am thinking one might be able to find a prop/reduction combo that could deliver a kilowatt at 5 knots, but not sure how much sail area would be required to overcome that drag.

[DotDun]

Originally Posted by KTP

I wonder if sizing the prop quite differently for best efficiency regen you would be able to get quite a bit more, while still remaining efficient for sailing and motoring. It would seem that for regen you want a quite large prop and a big reduction drive to your motor (3:1, maybe 4:1)? so that the slow speed of 5 knots produces quite a bit of power. I am thinking one might be able to find a prop/reduction combo that could deliver a kilowatt at 5 knots, but not sure how much sail area would be required to overcome that drag.

Nothing is free. You may get 1KW @ 5kts, turn regen off and you'd be doing 7kts.

[Capt Gill]

DotDun:
"Nothing is free."

Not exactly true, e.g., wind, currents & tide levels, solar are free; it's the harnessing of this energy that costs, some more or less than others.
Be wary of absolutes.

[AKA-None]

So is there any reason it must be either or. It would seem to me that a hunted approach as stated earlier might be a good next step in evolution. Main propulsion is sail, secondary for maneuvering is electric and if a big or sustained push is required then internal combustion. Realistically how many hours of travel do most people do with their engines vs sails? And yes many people use their sails as decoration rather than propulsion.

[KTP]

Originally Posted by DotDun

Nothing is free. You may get 1KW @ 5kts, turn regen off and you'd be doing 7kts.

Mmm, not so sure. I have had times where I am sure we were up against hull speed and had plenty (too much) wind. When the boat is pushing 10kW of water on the bow because it is exceeding designed hull speed, maybe 1kW of drag from the regen wouldn't knock off 2kts.

[DotDun]

Originally Posted by KTP

Mmm, not so sure. I have had times where I am sure we were up against hull speed and had plenty (too much) wind. When the boat is pushing 10kW of water on the bow because it is exceeding designed hull speed, maybe 1kW of drag from the regen wouldn't knock off 2kts.

That’s not what you said. You stated at a slow speed of 5kts, which unless your hull speed is 5kts, regen is taking speed away from the boat. I agree that when the sails are producing more power than the hull can use that regen makes sense, but in lighter winds, regen will cost in speed.

[skipmac]

Originally Posted by AKA-None

So is there any reason it must be either or. It would seem to me that a hunted approach as stated earlier might be a good next step in evolution. Main propulsion is sail, secondary for maneuvering is electric and if a big or sustained push is required then internal combustion. Realistically how many hours of travel do most people do with their engines vs sails? And yes many people use their sails as decoration rather than propulsion.

The main reasons for straight diesel power over EP plus generator in the terms you mention is cost, complexity and potentially weight

To have the option of EP for short range and adding range with on board power generation will cost double or triple what it costs for just a diesel engine. You have to have both an EP system and a large diesel generator to accomplish this. A diesel generator that produces even half the equivalent power of a straight engine is more much more expensive. In very round numbers, a 50-60 HP diesel engine installation will be $15-25,000. 50-60 HP equals 37-45 kW generator. Assuming with battery backup and other efficiencies you might get by with 1/3 to 1/2 that capacity you will spend as much or more just for the generator.

Then you still need to add the cost for the EP system which could be that much again. Then a large battery bank, more cost and a lot of weight AND the charging system for the batteries.

Of course the main propulsion would be sail but even long distance cruisers at times find need to use power for extended times. Certainly there are those like the Pardey's that never use an engine but they are a very tiny minority. The huge majority of cruisers find that supplementing sail with power in some situations can cut a passage time dramatically.