How feasible is 100% renewable electric cruising right now?

[GrowleyMonster]

Originally Posted by ranger42c

Umm... well... not so much, actually.

I take your overall point, but...

Our shorepower is individually metered. For others at marinas, it's likely calculated into the cost of the slip. Presumably for those with their own docks, the cost of shorepower might be incorporated into the household usage. And so forth...

-Chris

At a national average of 12 cents per kilowatt hour, yes it is practically free. Not absolutely free, no. But considerably less than a buck for a "fillup" for me and my 220ah 48v bank. But I forgot about marinas with included electricity which would make it actually, not practically free. Our three main marinas in New Orleans have individual metering.

[Peregrine1983]

Originally Posted by GrowleyMonster

a 42' boat at 6kt for 2 hours calls for a really big battery bank. You can roughly figure it this way. 1HP = approx 746w. Let's say you require 10HP to achieve that speed. So you estimate that you need 8kw for 2 hours, or 16kw/hrs Let's say you elect to use a 48v bank, or the prefab system calls for a 48v bank. If a different voltage, just do the math. Anyway, so you need 333ah of usable storage. For flooded lead acid batteries, you should not routinely discharge to below 50% SOC, so to get 333ah of USABLE storage you need 666ah rated capacity. Except that does not allow for high discharge rate Peukert Effect allowance. So you will need about 1000ah of storage at 48v. This would recommend single cell Rolls Surette 1000ah batteries, 24 of them. One likely candidate would be the S-1400EX. Weight wet is 127.5lb and remember, you need 24 of these. 17"H 13-3/8"L 7-1/8"W. Yes, you can reduce the weight by going with a slightly smaller bank of LiFeP04s since they can be discharged more deeply, but higher tech batteries come with their own set of problems in this type of application. Explore that idea, sure, but don't fall in love with it.

You can go higher voltage, but that won't really do much for reducing the weight and size of the bank. The only thing you could do to make it cheaper would be to go with a voltage high enough to get the same amount of energy from a series of golf cart batteries, but that would be about 145V and you would need a high voltage controller and motor for this. Also with that many connections, you will be continually busy just checking your intra bank connections.

So, you probably would want to re examine your power requirement and therefore your target speed. If you were okay with half that speed, you would probably cut your power needs to 1/3 of the above case, maybe less. You can still engineer the system to give you a reasonable top speed. One nice thing about electric is there is very little energy penalty for having a high power motor if you don't use it at high power. A big diesel at idle still sucks more fuel than a tiny diesel at idle. What I a saying is you could easily go with a 10kw or12kw motor and controller, but when you are running it at 1kw or less you get about the same performance as a 5kw motor running at 1kw. So, go with a big motor, but only use the power when you need it, not just when you are in a hurry or bored with going 2 or 3 knots.

If you can get your batteries down to lets say L-16 size, it would be a lot easier to place them not to mention buy them. I will let you find the specs and do the math on that one. Remember that 48v is sort of the sweet spot voltage for budget systems because of the large amount of equipment available such as chargers, inverters, controllers, DC/DC converters for your 12v loads, etc, and also wiring standards are different above 50v since it is considered the lethal voltage. (don't get carried away thinking about that... 48v CAN kill you, and 96v CAN be survivable, depending on a lot of factors.) Higher voltages mean higher reduction ratio, too. If you are going over 48v then you may as well go 96v or 120v or whatever, because 72v is already over the 50v threshhold. There is little to recommend a 60v or 72v system.

Electric propulsion is an idea that is easy to fall in love with. By that, I mean become so enamored with the concept that you pay little heed to reason, logic, or empirical data. Sort of like falling in love with the prom queen who later turns out to be the wife from hell, even though your friends all told you she was poison in a skirt before you married her. Don't dream too much into the idea. It can be VERY practical and economical, depending on your use. For a day sailer or weekender that has access to shore power charging and only needs power for docking, electric is wonderful, and is totally superior to infernal combustion propulsion in every way. For others, it is marginally better, or inferior. For some others it is totally impractical. At your performance specifications, it isn't very practical. Loosen up on the speed and it might be worth considering.

I love my electric boat. I have about a quart of diesel onboard, and that is just for cooking. I never visit the fuel dock, never spill fuel, never smell fuel. Shore power charging is waaaaaay cheaper than liquid fuel. Pennies to putter around all day. Very quiet, especially at low power settings and with the hatch closed. Sometimes I can't even hear my motor. Instant power. No warmup. No maybe maybe when I hit a start button. Crazy maneuverability due to not having a minimum idle speed. For a sailboat, especially one that is hard to tack, a twist of the knob and suddenly you are hove to if you kept the jib aback, or on the other tack if you shifted to the new jib sheet. The instant burst of speed can be very handy if you find yourself being blown down on a bridge abuttment or something like that. I installed my drive system for about 1/4 of what a new diesel would have cost, and that includes my batteries. But I had to come to terms with the limitations imposed by having only 220ah at 48v, and being unable to afford bigger batts than that.

You should probably check with your owner's group and see if anyone else has electrified the same boat, what their performance data looks like, and the specs for the system. Start with some actual empirical data as you decide whether or not to go electric.

Hybrid can work, yeah, but if you can't charge from shore power and can't mount a minimum of 600w of solar where the sails won't shade the panels, you would be better off with just the diesel. Shore power is nearly free energy. Solar too, except of course for the considerable cost of panels and controllers. Hybrid is inherently inefficient energy wise, but free energy can make up the difference. Of course there are other reasons to consider hybrid, but make sure that they are really important to you.

Obviously, considering the weight, your old fuel tank location is not necessarily the best place for your batteries. Typically you want them near the keel area, and mine are right where the companionway steps used to be. It was tempting to put them where the old fuel tank was, but nah. I didn't want all that weight so far aft. I can probably add a second bank up forward and not put her too far out of trim. Figure out the weight of batteries and battery trays and hold downs and cable and stuff, then have an equal weight of people move around foreward and aft while you look at the trim. It could change the way your boat handles under sail. Down by the head and she will probably have a tedency to round up. Down by the stern and she will want to fall off. Sure, you can compensate with sail adjustment, but that is not always a perfect fix if it changes your slot enough to degrade performance. If you are talking 600lbs of batteries, no big deal unless they are waaaaay aft or forward. 1800lb of batteries is a whole nother critter.

Really interesting post. Thanks. Hope you didn't marry the poison in the short skirt...

It sounds like a diesel electric hybrid could be a consideration for my cruising style, but if I've still got an oil burner aboard it certainly dulls the appeal. Love the idea of the instant and SILENT power though...

[GrowleyMonster]

Originally Posted by Peregrine1983

Really interesting post. Thanks. Hope you didn't marry the poison in the short skirt...

It sounds like a diesel electric hybrid could be a consideration for my cruising style, but if I've still got an oil burner aboard it certainly dulls the appeal. Love the idea of the instant and SILENT power though...

Well, the rough and ready answer to that is to hang an electric outboard on your stern. You can build one with a BLDC motor and controller and the non running carcass of a long shaft gasoline outboard. For very short runtime at low (5a or so) power, you can use say a 20ah 48v e-bike battery for power. If you got two of them, better. Best to have a bank of lead acid, though, IMHO but the ebike battery is a portable solution you could use for the dinghy, too. You can also buy ready built electric outboards. I personally think the Torqueedo units are overpriced but you get a popular brand name and reportedly fair to reasonable support. A BIG (100 lbs thrust or better) trolling motor ran with a cheap external PWM controller fed from a 48v bank would maybe do the trick, just for docking, and not in extreme conditions. Pretty marginal for that size boat, but something cheap to try that you could still use for the dink. I think a 10kw or better proper electric outboard would be better though.

Another option would be to roll yer own hybrid. Remove the coupling flange from the prop shaft and mount a pulley on the shaft, then recouple. Oh, put the belts on before you couple it back up. You want either a wide timing belt type pulley and belt, or multiple vee belt setup. A single vee belt will fail on you pretty quick. The advantage of the vee belte out of gear, turn up the regen. Trailing prop will then be charging the batteries. If you take the engine out of gear you can use the electric motor for propulsion. Have it standing by for tacking and stuff, for a really slick maneuver single handed. Have it barely turning over to eliminate prop drag. Run it for electrosailing when the wind is just barely puffing. Use the els is you get them for a few bucks at any gas station. Anyway you build a mount for the motor that puts the motor over the shaft and that you can adjust the tension on. Choose your pulleys to give you the reduction ratio that you want. Typically this will be 2:1 up to 3:1 but you can experiment with this later for peak efficiency at your desired electrocruise speed. Make sure your motor has a temp sensor and the controller accepts input from one, and the first few times you run it, shoot it with an IR thermometer. The motor casing should never get over about 145 degrees f. If it does, your reduction ratio is too low, you need the motor turning fast enough to self cool with the internal fan.

With the engine turning, you turn the motor controller regen all the way down or off for least drag from the electric motor. Prop is turning, batts are not charging. If you want to charge your bank, turn up the regen, and you have prop turning, batts charging. If you are under sail and going really fast and have a big enough prop, with the enginectric for when you need to pinch really tight to the wind. Use the motor to slip out silently or to sneak up on alligators or sea cows or other aquatic life. Its a thing, yeah. Gives you something to tinker with, too.

One nice thing

[GrowleyMonster]

Originally Posted by Peregrine1983

Really interesting post. Thanks. Hope you didn't marry the poison in the short skirt...

It sounds like a diesel electric hybrid could be a consideration for my cruising style, but if I've still got an oil burner aboard it certainly dulls the appeal. Love the idea of the instant and SILENT power though...

Well, the rough and ready answer to that is to hang an electric outboard on your stern. You can build one with a BLDC motor and controller and the non running carcass of a long shaft gasoline outboard. For very short runtime at low (5a or so) power, you can use say a 20ah 48v e-bike battery for power. If you got two of them, better. Best to have a bank of lead acid, though, IMHO but the ebike battery is a portable solution you could use for the dinghy, too. You can also buy ready built electric outboards. I personally think the Torqueedo units are overpriced but you get a popular brand name and reportedly fair to reasonable support. A BIG (100 lbs thrust or better) trolling motor ran with a cheap external PWM controller fed from a 48v bank would maybe do the trick, just for docking, and not in extreme conditions. Pretty marginal for that size boat, but something cheap to try that you could still use for the dink. I think a 10kw or better proper electric outboard would be better though.

Another option would be to roll yer own hybrid. Remove the coupling flange from the prop shaft and mount a pulley on the shaft, then recouple. Oh, put the belts on before you couple it back up. You want either a wide timing belt type pulley and belt, or multiple vee belt setup. A single vee belt will fail on you pretty quick. The advantage of the vee belte out of gear, turn up the regen. Trailing prop will then be charging the batteries. If you take the engine out of gear you can use the electric motor for propulsion. Have it standing by for tacking and stuff, for a really slick maneuver single handed. Have it barely turning over to eliminate prop drag. Run it for electrosailing when the wind is just barely puffing. Use the els is you get them for a few bucks at any gas station. Anyway you build a mount for the motor that puts the motor over the shaft and that you can adjust the tension on. Choose your pulleys to give you the reduction ratio that you want. Typically this will be 2:1 up to 3:1 but you can experiment with this later for peak efficiency at your desired electrocruise speed. Make sure your motor has a temp sensor and the controller accepts input from one, and the first few times you run it, shoot it with an IR thermometer. The motor casing should never get over about 145 degrees f. If it does, your reduction ratio is too low, you need the motor turning fast enough to self cool with the internal fan.

With the engine turning, you turn the motor controller regen all the way down or off for least drag from the electric motor. Prop is turning, batts are not charging. If you want to charge your bank, turn up the regen, and you have prop turning, batts charging. If you are under sail and going really fast and have a big enough prop, with the enginectric for when you need to pinch really tight to the wind. Use the motor to slip out silently or to sneak up on alligators or sea cows or other aquatic life. Its a thing, yeah. Gives you something to tinker with, too.

One nice thing

[Nikki S]

I know some folks who last year put electric motors on the 40 ft cat they built, but they didn't cut the mustard so had to replace them with diesel.
I Would love to hear success stories, though.

[ranger58sb]

Originally Posted by GrowleyMonster

At a national average of 12 cents per kilowatt hour, yes it is practically free. Not absolutely free, no. But considerably less than a buck for a "fillup" for me and my 220ah 48v bank. But I forgot about marinas with included electricity which would make it actually, not practically free. Our three main marinas in New Orleans have individual metering.

Not to worry, I think I was just quibbling about the difference between "cheap" (inexpensive) and "free."

I reckon when it's "included" at marinas, they've simply added the anticipated, maybe average, cost of electricity. Perhaps quibbling again...

-Chris

[SecondBase]

Originally Posted by Dockhead

Some people cruise without any engine at all. So 100% renewable cruising is absolutely feasible.

And humanity has at least a couple millennia more of experience sailing without engines than sailing with engines.

Here is a recent solar-only-powered Atlantic crossing.

http://www.transatlantic21.org

[skipmac]

Originally Posted by SecondBase

And humanity has at least a couple millennia more of experience sailing without engines than sailing with engines.

Here is a recent solar-only-powered Atlantic crossing.

transatlantic21: The world's first crossing of the Atlantic on a solar boat

Just a caveat. Cruising with no engine is certainly possible and is still done by a few. Just remember in the old days of sail ships often sat in port for days or even weeks waiting for a fair wind and tide to put to sea.

Getting into ports often involved putting the crew in a long boat to tow the ship to a berth or in later days, hiring a steam tug. Even Joshua Slocum was frequently towed into ports. No engine will eliminate cruising the ICW or any of the canals in Europe.

[Peregrine1983]

The wikipedia chart of energy contained in various "fuels" is pretty fascinating:
https://en.wikipedia.org/wiki/Energy_density

Lists the specific energy of everything from Uranium (80,620,000 MJ/kg), to diesel (48 MJ/kg), to Wood (16.2 MJ/kg), to a lithium battery (1.8 MJ/kg).

Really gives you an idea of what you're up against with energy storage in batteries.

[valhalla360]

Originally Posted by Peregrine1983

Was just reminded of my favorite Grandpa Simpson quote: "I used to be with it! Then they changed what "it" was. Now what I'm with isn't it. And what's "it" seems weird and scary to me. It'll happen to you someday!"

Anyhow, obviously this technology is developing rapidly and what I'm proposing is not far off. My question is - is this feasible now?

Technology really hasn't changed much. Electric motors have been very good for more than half a century. It's easy to spec an electric motor that will match or out perform a diesel in just about every facet.

Lithium batteries have been around for quite a while also. Batteries are where electric power falls down.

26hp is doable but a little light. As long as you want to top out around 6kts, it's probbly adequate. If you ever want hull speed or to make headway against bad conditions, it's questionable.

At 6kts, I would expect you will be pretty close to 20kw output (hard to say with certainty but if the boat was spec'd with 58hp, it makes sense as 58hp would be a little more than needed for hull speed. So 2 hrs will use 40kwh. You can't use 100% of a battery bank. About 50% for lead acid and about about 80% for lithum...net effect you need a 50kwh lithum battery bank or an 80kwh lead acid.

Bigger issue is your use case. 2 hrs at 6kts is basically little more than enough to get in and out of port. Some potential use cases:
- Typical cruiser: You want 10-20hrs at 80% of hull speed in adverse conditions. This makes choosing destinations and route easy but also if you get in a bad position, you can motor out of it. It's not uncommon to have enough for 3-6 days of motoring at these speeds. 10hrs (lower limit) would need 200kwh. An 85kwh tesla battery bank runs $15k, so figure maybe $40k in batteries. From a practical point of view, doesn't work.
- Weekender/Purist Sailor: This is someone who only uses the motor to get in and out of port. Downsides are that if the wind dies, you may be stuck until it returns. Also, expect a big drop in resale value as most of your potential buyers fall in the prior typical cruiser category. You can extend the range with say a 40kwh battery bank if you are willing to poke along at 2-3kts. Power demands increase exponentially as you reach hull speed so dropping back seriously lowers power demand. The catch is if you are fighting a strong headwind/current/waves, it doesn't drop that much. With a 25hp outboard on our prior 34' catamaran, I can recall full throttle making 3kts against a 30kt headwind.
- Hybrid: This is doable but is more expensive up front and less efficient than just a straight diesel. Big problem is if you size the generator for propulsion is way oversized for house loads. If you size it for house loads, its too small for propulsion.

Solar/Wind: They just don't produce enough power to be meaningful. 20kw of panels would cover several boats the size of yours and they only put out their rated power for around 4-5hr (equivilent) per day.

[valhalla360]

Originally Posted by TheThunderbird

Big ship propulsion is usually electric, with diesel engines used for producing electricity. More efficiency, control, no gear- box...

Big ships, trains etc..., are almost exclusively about the complications with adapting a transmission to engines rated in the thousands of HP.

It's actually less efficient once up to speed but the size and complexity of a mechanical transmission would be incredible. Imagine trying to let the clutch out on 5 train engines simultaneously without stalling one.

Electric motors make it easy to control.

PS: Simple single engine freighters sometimes use direct drive with no transmission and rely on tugs for in port maneuverability.

[valhalla360]

Originally Posted by roland stockham

On the issue of electric being 'more powerful' than diesel the way I read it is that the additional low speed torque enables you to swing a larger more efficient propeller. Combustion engines are much less efficient and powerful at lower rev's so it is really a claim thet a smaller electric engine is 'as useful' rather than 'as powerful' but I have no experience to know if the claim is true. Certainly diesel electric has some significant advantages including range so if your batteries are going to be heavier and more expensive it would seam to make sense to fit smaller batteries and a generator (DC if possible).

Common error. If it was all about a giant prop and torque. It would be easy to add a reduction gear to multiply the torque on a diesel and get the same efficiency advantage.

Reality is a 40' boat swinging a 6' prop is theoretically very efficient but very impractical.

[valhalla360]

Originally Posted by GrowleyMonster

At a national average of 12 cents per kilowatt hour, yes it is practically free. Not absolutely free, no. But considerably less than a buck for a "fillup" for me and my 220ah 48v bank. But I forgot about marinas with included electricity which would make it actually, not practically free. Our three main marinas in New Orleans have individual metering.

If I'm calculating correctly: if you 100% depleted your bank, that's around 10kwh of storage. Reality is probably closer to 50%, so 5kwh.

A gal of gas holds about 33kwh of energy. Assuming 1/3 efficiency converting that to actual propulsion that means your tank holds the equivalent of about 1/2 gal of gas.

So $1 vs $1.5 for 1/2 gal of gas. Cheaper per gallon, yes but definitely not free.

PS: slips including electricity are premised on traditional use which is limited to house loads. If significant numbers of boats were charging propulsion banks, you could expect the slip pricing to change accordingly.

[GrowleyMonster]

Originally Posted by valhalla360

Big ships, trains etc..., are almost exclusively about the complications with adapting a transmission to engines rated in the thousands of HP.

It's actually less efficient once up to speed but the size and complexity of a mechanical transmission would be incredible. Imagine trying to let the clutch out on 5 train engines simultaneously without stalling one.

Electric motors make it easy to control.

PS: Simple single engine freighters sometimes use direct drive with no transmission and rely on tugs for in port maneuverability.

Nearly always a ship of over 10,000 tons will have direct drive low speed diesel. To reverse, the engine is stopped, and started in the opposite direction. These days most newer ships will have a bow thruster, sometimes a stern thruster as well. Tugs are usually still called, out of an overabundance of caution and concerns about litigation, as well as local port state authority compliance. Diesel electric drive is used primarily on ships that have extreme maneuverability requirements such as ships that service undersea communications cables, or dredges, or large tugs or drill ships. Some cruise ships, also. Ships with straight diesel propulsion typically have electric bow thrusters.

[StuM]

Originally Posted by valhalla360

If I'm calculating correctly: if you 100% depleted your bank, that's around 10kwh of storage. Reality is probably closer to 50%, so 5kwh.

A gal of gas holds about 33kwh of energy. Assuming 1/3 efficiency converting that to actual propulsion that means your tank holds the equivalent of about 1/2 gal of gas.

So $1 vs $1.5 for 1/2 gal of gas. Cheaper per gallon, yes but definitely not free.

PS: slips including electricity are premised on traditional use which is limited to house loads. If significant numbers of boats were charging propulsion banks, you could expect the slip pricing to change accordingly.

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)