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Crazy Propulsion idea for next cruiser... Thoughts...

8K views 61 replies 15 participants last post by  JohnBPrice 
#1 ·
Hello all,

I've been dreaming about electric propulsion for my next cruiser. Looking at something like a Jeanneau Sun Odyssey 379 or 389
(38 foot). My plan is the set this up as my last boat to last me well into and past retirement. I'm sold on the idea of the lower maintenance of the electric drive and the simplicity of a one fuel cruiser. A large bank of lithium cells will allow all the conveniences of an induction range, microwave and possibly even A/C on the odd night at anchor. No need for diesel or propane tanks.

There are a few offerings for electric sail drive systems on the market and I've gotten the white sheets from most of them.
My initial idea was a 14KW sail drive and a bow thruster for better maneuverability as I'd be in the back row of the tight marina.

Then I had a thought. Why spend the additional 10K on a bow thruster install? Instead of one sail drive, how about 2 smaller units (7KW) installed port and starboard of center. My thoughts are 1) that smaller drive motors would be better at regenerating at lower speeds than one large unit and 2) while in the marina, two props give you the ability to steer the bow by reversing drive on one prop. Catamaran level steerage skills on a monohull may be possible.

Any thoughts????
 
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#2 ·
Have you done the simplest audit of the daily energy requirements of your boat?

How are you planning to recharge these lithium batteries.

Even if you were to cover every available horizontal space with solar panels you will not get anywhere near enough to run A/C.

I know of a few that have gone the electric power route and they have all fitted generators.
 
#3 ·
You would lose the prop wash effect, since your prop would no longer be behind the rudder (unless you have one of those new twin-rudder boats).




This is completely out of my area of expertise, consider me nothing more than a guy at the bar chiming in, but... With twin props if you're counting on regen while under sail wouldn't one of the props be out of the water if you were heeled at all? That would cut your regen in half.
 
#4 ·
Asymmetrical dual prop thrust on a mono hull is still not going to perform like a catamaran or ********. The primary purpose of the keel is to interfere with pushing aside. The bowthruster gets away with it, as it provide thrust exactly perpendicular to the keel and most often at a further leverage distance.

Aside from your question, the overall design thought may be from the future. I don't think there is such a lithium setup that is going to do all that you want, at least not for very long. Then, you have to recharge it. Hopefully, such options exist at some point. For now, the motivation to get away from diesel maintenance are a valid motivation. Albeit, you won't go very far, without a fuel burning generator. You're not going to get battery powered air conditioning and induction cooking at the same time.
 
#5 ·
Up until last month, we had an electric stove/oven. The change has cut our generator time by about 50%.
We have a fairly large solar array and a wind gen, and we couldn't possibly meet our energy needs with both because some days there just isn't enough sun and/or wind to keep up with even half our energy needs.
As TQA mentioned, your going to need an auxiliary charging system unless you are just day sailing, and plug in every night. Calculate the energy requirements of an electric stove, motive power, and a thruster, not to mention A/C, and you are going to find them astronomical even with a generator. In the end, it's just simple math; can you replenish the energy you consume with any system other than shore power? If not, you are going to get stuck w/o power sooner or later.
If I were to put a thruster on a small sailboat, which I wouldn't do for any reason, I'd go to a hydraulic unit. Electrical systems are the weakest and most susceptible to problems on any vessel.
As for twin screws on a small sailboat, the props are not going to be far enough apart to give you the control you expect, even with twin rudders.
 
#7 ·
postdoc, it doesn't hurt to get creative in your thinking, and electric propulsion is wonderful if it suits your usage, but basically you're looking at the following solution as a good proposal:
  • I assume you're buying a used boat;
  • Remove and sell off your diesel propulsion engine, replace with a suitable electric motor setup;
  • Install a generator set powerful enough to quick charge your huge lithium bank and powerful enough to power your electric propulsion motor to at least 50%;
  • Install induction stove top, not "electric" resistance stovetop;
  • Mount as much solar as you can without the boat starting to look ridiculous;
  • Forget about the thruster. Use the money to pay for the genset (in a silent box) and perhaps some boat handling lessons to improve your confidence while docking.
 
#8 ·
Interesting idea and concept. I've had an EP boat for over ten years now and keep discovering new ways to use it. Things you would never do with a diesel. For example in light winds I crank the motor control a tiny bit to turn the prop just enough to eliminate prop drag. You could do the same with your forward and aft prop idea. Gives you a nice bump up in boat speed and automatically starts regenerating once the wind picks up and no folding mechanical prop issues.

Another idea I've been thinking about. I have a electric outboard for the dingy. I was thinking it would be great to have something like it that would drop down from the bow on a rail for when one needed a bow thruster and pull it up out of the water when under way. I saw something similar being used on a power boat.
 
#9 ·
Until there is a significant technical breakthrough, all electric boats are going to be limited to daysailing or marina hopping. Just compare the amount battery storage you would need to equal the energy in say 10 gallons of diesel fuel.

If you are going to have a large diesel generator onboard, I don't see the big advantage over a direct drive diesel for propulsion.
 
#10 ·
If you're serious about making your boat more maneuverable, you could install an electric pod motor that rotates 360 but locks forward when sailing. I imagine that would be fairly expensive, though.

As far as a general electric conversion goes, you have to be willing to accept both the benefits and limitations the system will impose on you. For my electric conversion, I went with lithium batteries, and saved about 100lbs net after pulling all the diesel components out.

Benefits of electric propulsion include much higher reliability and motor endurance, instant power, regeneration under sail, easy diagnostics and part replacement, universal recharging, and almost no or no maintenance, depending on the motor you choose.

The only real limitation is range, but it's a pretty big limitation. Expect ~1/10th the range of the diesel you replace, assuming you don't have a generator. That being said, a lot of sailors rarely use more than 1/10th of their diesel tank on any given outing. Personally, I'm generally daysailing, so I just need enough to get out of the marina and back in, plus a little more for emergencies.

If you're in a slip on shore power the vast majority of the time, an all electric setup makes sense. If you're making passage and anchoring a lot, you're going to need a both a generator and a very large battery pack to make that kind of system viable. Both electric cooking and electric propulsion take an enormous amount of energy to run. I'm not saying it's impossible, but you'll need much more electric generation than an average boat to make it work.
 
#11 ·
Thank you all for the feedback.
I hadn't thought of the resistance that the keel would cause when trying to pivot the bow from the back. A bow thruster is more energy efficient in that regard. And yes, It's always better to have skill over equipment ad equipment fails. A bow thrusters on 38 footers are becoming more common on newer boats as its much cheaper than an emergency hall out and a repair. My wife tends to take the helm and I go forward when docking. I'd like her to have the extra control of the thruster if an emergency arrises.

I still haven't been able to track down any real number on regenerative capture of energy under sail with different sized motors. Two smaller may still work out better but I'm still looking for the data.

Our energy needs are manageable even with a 14KW lithium bank. I know some of you worried when I mentioned A/C and induction cooking. Like motoring, they would be done only occasionally. I find that we rarely motor more than 10-15 miles in my current boat.

Thank you all for the great feedback.
 
#12 ·
I still haven't been able to track down any real number on regenerative capture of energy under sail with different sized motors. Two smaller may still work out better but I'm still looking for the data.
I searched high and low for this kind of data for months and came up with essentially nothing. Lots of speculation, most of it seemingly crazy optimistic or pessimistic. No actual data, though.

I just received my boat-mounted multimeter. This displays Volts, Amps, KW used, current wattage, and a host of other good info. Once I'm back in the water, I'll be able to give you all the data you want on my motor/prop combo. I'm curious myself as to what regen I'll be able to get and at what speed.
 
#13 ·
I’m a little old fashioned in my boating so to me electric propulsion on a boat is nothing more than smoke and mirrors. But having said that . . .

I try to sail as much as possible so propulsion would be limited to getting on and off my mooring and in and out of anchorages so the time the electric motor (EM) will run would be minimal. My last ocean crossing, my engine ran for 38 minutes in 7 days. But . . .

Surely if you are dependant on the EM for propulsion and don’t want to run a genset all the time to put back what you use, one would try to steer clear of stuff that uses the same energy source. For example:

- why an electric stove when gas cookers have worked since forever?
- if you’re going to have an EM, hot water for showers etc. needs to be specifically generated so you’ll probably need gas on board anyway (please not another electric appliance, I know the electric heater in our califont murders my electricity reserves).
- why an electric bow thruster on an essentially smallish boat, many thousands of which have been in service since forever without thrusters?
- why AC when many boats much bigger than 38ft don’t have it? Electrically unaffordable luxury IMO.

If I were to contemplate an EM, I would want as much electrical capacity for propulsion as I could get and would work really hard at eliminating anything else that would compromise that ideal. If you must have one electric device, make it a small watermaker.
 
#14 ·
I think of electric motors on yachts just like electric motors in cars. The first ones were average. Wait a year and they get better real quick. Perhaps a selfish approach, albeit one you'd agree with if you're looking at setting your yacht up once and for all for retirement. Perhaps wait a while until the industry and technology catches up with the car industry, and then make the move for electric.
 
#15 ·
Consider that 10 years ago, the electric vehicle market consisted of a single super-expensive roadster made by a half-baked startup that was tripping over it's own feet to get off the ground.

5 years ago, there were about 10 models, with only two having more than 100 miles of range.

Today, there are 40+ models, and the vast majority have 200+ miles of range, some with 300+ miles.

Some car companies have committed to 100% EV or hybrid lines within the next 10 years.

The electric revolution is here. It's only a matter of time before this revolution makes it's way into the marine world.

Electric motors are superior to ICE motors in every measurable way. The only remaining advantage that ICE has is energy density of the fuel (you can go a lot farther on 1lb of diesel than you can on 1lb of even the very best batteries). Once that advantage is reduced, there will be no reason to have an ICE on your boat, other than nostalgia.
 
#24 · (Edited)
I often hear people citing concerns about the unreliability of wind and solar power and the issue of being able to store energy to balance the peaks and lulls in usage and production. One of the first answers that seems to get floated is the idea of very large battery banks storing energy during peak production periods to be used when production is less than usage. From everything that I have read, the ability to do that cheaply and efficiently is a long way off and frankly in many (most) large scale applications may never be viable.

But, since the late 1960's there have been a number of very large, efficient, and relatively inexpensive to build and operate energy storage facilities around the country and the world. In operation these are essentially carbon neutral (although there is certainly embodied energy in building one). These systems are typically referred to as some variation of "Pumped water energy storage facilities". There are literally dozens of them in the US at this point, but the largest two are in these links below:

https://en.wikipedia.org/wiki/Ludington_Pumped_Storage_Power_Plant
https://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Station
https://www.dominionenergy.com/comp...tion/water/bath-county-pumped-storage-station

Obviously these are not portable power in the same way that carbon based engines, fuel cells, solar panels, and wind/water driven generators are, but they do allow balanced energy sourcing that has a greatly diminished dependency on carbon based power sources from renewable sources that can be accomplished with a readily available technology source.

Jeff
 
#26 ·
Perhaps if the electric powered vessel remains coastal/local then comparing battery capacity of a car with fuel (diesel/petrol) capacity of a similar car works. But when you’re talking boats that go further afield that comparison loses validity. Why? Well simply because few cars have 400 litre fuel tanks.

I reckon it’ll take a while before a practically usable battery bank that will work on a boat can match the energy density of that much fuel.

Disclaimer: I just heard the term “energy density” a few minutes ago for the first time 🙂. Perhaps my opinion above needs adjustment.
 
#30 ·
Perhaps if the electric powered vessel remains coastal/local then comparing battery capacity of a car with fuel (diesel/petrol) capacity of a similar car works. But when you're talking boats that go further afield that comparison loses validity. Why? Well simply because few cars have 400 litre fuel tanks.

I reckon it'll take a while before a practically usable battery bank that will work on a boat can match the energy density of that much fuel.

Disclaimer: I just heard the term "energy density" a few minutes ago for the first time ?. Perhaps my opinion above needs adjustment.
Ah, but a car has no way to generate energy while in motion. A gas tank is just a type of battery - once it's gone, it's gone until you find a place to refuel. Sailboats, on the other hand, have several ways to draw fuel in from the outside. An all electric boat can generate fuel via wind, solar, or propeller drag while under sail. Hell, you could even put a bicycle generator on there, if you think the roughly 1/4 horsepower your legs can generate is worth it. That's about a kWh every 3 hours of pedaling. Good exercise, though. :p

Power boats are a whole other story. They are generally *ridiculously* inefficient, with very few exceptions. It will be a long time before electric power becomes practical in that realm. Only little super-efficient (read:slow) trawlers like the Albin could even consider a conversion at this point.

Power density is energy per unit of weight, generally expressed in WH/kg. Diesel's energy density is 11.6 kwh/kg. Modern lithium batteries are around .25 kwh/kg. Lead acids are around .05 kwh/kg. These numbers are a little misleading, as electric motors are more than twice as efficient at converting energy into work than a diesel is. If you normalize the numbers, it's closer to 5kwh/kg useable for diesel. Even so, that's a 20-fold advantage for diesel over current lithium.

Batteries have a long way to go to catch up to diesel.
 
#27 ·
The only subtle difference on a cruising sailboat is it can “refuel” it’s batteries via solar, wind or hydro. However, the point stands. That technology isn’t efficient enough to reliably replace the amount of time/distance one can get out of a tank of diesel. At least not yet.
 
#33 ·
Natural gas is great because it can be ramped up and down quickly to respond to need, whereas nuclear and coal are more fixed. Hydropower can also be ramped up and down quickly.

However solar and wind aren't as intermittent as you might think, because the electrical grid can smooth out shortages in one area by bringing in electricity from another. Advances in grid technology will open up other options for regulating power, like demand pricing.

I work at a manufacturing plant that uses a fair amount of electricity and right now we have a fairly crude system of demand pricing: if it's going to be a high demand day they call us and ask us to shut down a certain amount of load. We can opt to go over that, but we pay a significant fee.

I can imagine systems where you'd plug your car or boat in, but set it so that it won't start charging until the price of electricity drops below a certain threshold (which would probably be sometime in the middle of the night). High electric consumers like aluminum manufacturing would vary production based on price.
 
#34 ·
Natural gas is great because it can be ramped up and down quickly to respond to need, whereas nuclear and coal are more fixed. Hydropower can also be ramped up and down quickly.

However solar and wind aren't as intermittent as you might think, because the electrical grid can smooth out shortages in one area by bringing in electricity from another. Advances in grid technology will open up other options for regulating power, like demand pricing.

I can imagine systems where you'd plug your car or boat in, but set it so that it won't start charging until the price of electricity drops below a certain threshold (which would probably be sometime in the middle of the night). High electric consumers like aluminum manufacturing would vary production based on price.
Exactly. Not only does production tend to balance out over larger regions but demand does too (i.e., California uses a ton of power for AC in summer, when power demands are relatively low in the PNW - summer is when we generate a lot of solar in the NW and don't need all of it. similarly CA is still producing solar power in winter when we need it for heating and they don't so much). We just need a good grid to move it round.

Also, charging your car at low-demand times is doable (and done) now. That makes a ton of sense where the base power production is on all the time but not heavily used at night.

As others have noted, the range issue has largely been solved for EVs. A 300 mile range is more than enough for almost anyone so long as rapid charge stations are available along highway for long road trips, and they are being installed fast (especially if you own a vehicle made by the "half-baked startup" that someone mentioned, which is building its own network). We have a Leaf with a 107 mile range and even that is enough for almost everything we do in the urban area.

But the difference between cars and boats, and the real problem for electric boats, is that by the nature of a car you are almost always going to be somewhere you can recharge on a daily basis. Not so much the sailboat. It's hard to imagine using one for anything but short trips without some way to recharge, like a genset. That in itself is not horrible - you would in effect be operating like a plug-in hybrid car, which saves a ton of fuel. I know someone with a plug-in Prius who gets gas every 2-3 months.
 
#35 · (Edited)
IMHO the really scary thing about nuclear power is the time it takes to build a power station. Sure the current time is around 10 years that is 6 months to a year of work and 9 years futzing around with politics and health and safety.

But if the lights start going out and people are facing rolling power cuts and industry has to shut down I bet there will be some fast tracking and the risks will go up, way up especially as there will be less training time.

BTW The French have 68 working nuclear power stations.
 
#42 ·
It takes a lot more than 6 months just for the construction. But like any project, it's subject to staged inspections, and that does add time. Well worth it, considering the consequences of a catastrophic failure.

There are plenty of ways to mitigate demand other than building new plants. Here in MD the utilities do things like offer rebates for buying high efficiency appliances, educate people on why they should dump incandescent bulbs, offering incentives to charge electric cars at night, etc.

France has a mostly-nuclear grid for a very good reason. After the oil shock of 1973 (France as mostly oil-based electric at the time), they decided to make themselves fossil fuel independent, and went mostly nuclear. As of about 2008, they've started replacing their nuclear with renewables, with the goal to drop to 50% nuclear by 2035. They also export electricity to the tune of about 3B Euro a year, so there's a big financial incentive to keep electricity cheap enough to export. Hence they were a bit late to the game with solar and wind. They don't have the same pollution issues most other countries have.
 
#54 ·
95% hydro is clearly the big answer. Not available everywhere. There is an interrelated dynamic downstream with these dams that I don't fully understand. I suspect they are more impactful than we realize.

When an entity is government owned, it does not take away the profit motive. It only allows them to compete, without paying taxes, which does reduce cost. By extension, everything could be cheaper, without taxes. If these government entities don't profit, they can't afford to rebuild infrastructure, add new dams, etc. Unless, of course, the government provides that with other tax payer funds, it which case, that isn't the all in cost of producing juice.
 
#55 ·
95% hydro is clearly the big answer. Not available everywhere. There is an interrelated dynamic downstream with these dams that I don't fully understand. I suspect they are more impactful than we realize.

When an entity is government owned, it does not take away the profit motive. It only allows them to compete, without paying taxes, which does reduce cost. By extension, everything could be cheaper, without taxes. If these government entities don't profit, they can't afford to rebuild infrastructure, add new dams, etc. Unless, of course, the government provides that with other tax payer funds, it which case, that isn't the all in cost of producing juice.
Geography definitely plays a big part of why Quebec generates electricity the way it does. Canada as a whole is 60% hydro power. Again, geography.

Quebec Hydro is a state run monopoly. There's literally no one to compete against. It's run as a chartered crown corporation, which means that any time it wants to do something big, a group of lawyers looks at the charter and if it's within the charter's parameters, it goes to the legislature for a decision. This includes things like rate hikes, building projects, etc. The legislature consults with experts and makes a decision. More than once proposals have been shot down as an unnecessary expense. This includes things like CEO raises, bonuses, etc. Consider that the CEO of Quebec Hydro made about $800k last year, including bonuses. Contrast that with the CEO of Pepco making $15.4 million and you can begin to see the advantages of state run utilities. It's hard to get greedy when every major financial decision has to be run by the provincial legislature.

As an aside, there's no money in Canadian politics - everyone runs on state money, the elections are short, and everyone gets the same amount. Without mountains of dark money to influence elections, the politicians are beholden to the people who elected them, not the people who financed them.
 
#57 ·
I have some numbers to share.

I had Khaleesea out in nice, strong wind and was able to get her up to hull speed (thank you, Chesapeake summer doldrums, for giving me a break).

At 7 kts, I was getting ~15 amps of regen at 48V. That's 60A at 12V or 1440 amp-hours a day.

While I acknowledge that Khaleesea probably couldn't maintain that speed all day (at least not comfortably) I'm told that 7kts constant is pretty reasonable in most 40'-ish catamarans while making passage. With dual EP drive, that's a daily power budget of a whopping 2880 amp-hours a day, and that's assuming it's a dual motor setup like mine, which would probably be under-powering the boat by a fair margin. Larger motors and props could generate quite a bit more.

It could turn out that a dual-EP catamaran has the opposite problem most boats have - it generates too much electricity when under sail. You could counter that by running the motors for a couple of hours a day to give you an extra knot or two for a few hours each day.

You'd still need solar and/or wind for when you were at anchor, of course.
 
#58 ·
It could turn out that a dual-EP catamaran has the opposite problem most boats have - it generates too much electricity when under sail. You could counter that by running the motors for a couple of hours a day to give you an extra knot or two for a few hours each day.

You'd still need solar and/or wind for when you were at anchor, of course.
That was the problem the first electric Lagoon delivery crew had when crossing the Atlantic. They had to run the air conditioning to keep enough load on so as to not overcharge the batteries.
 
#62 ·
@postdoc, if you have the money and inclination to try dual electric motors, I think you should try it. Not many people have tried it, so you'll get all the stuck in the mud nay sayers telling you why it won't work or you will cause a rift in the universe if you even try.

My two cents: Twin screws give you reliability if one fails. You can always add a bow thruster too if you like. You can always pull them out and go back to single electric, it will cost money though. The money is the only real reason why you shouldn't do it.

On a different note, I am astounded by the number of people here who hate electric power and all the crazy reasons why it won't work Or is somehow evil. Thousands of people already have electric power, you can order it as an option on new boats or buy electric repower systems. It clearly does work. Sure it has benefits and detriments, but every system on a sailboat does. The best thing to me would be that it is quiet. If I wanted to motor around with the roar of engines and have a motoring range of hundreds of miles I'd buy a power boat.
 
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