SailNet Community banner

1 - 20 of 62 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #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????
 

·
Bombay Explorer 44
Joined
·
3,619 Posts
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.
 

·
Registered
Joined
·
2,953 Posts
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.
 

·
Registered
Joined
·
22,348 Posts
Asymmetrical dual prop thrust on a mono hull is still not going to perform like a catamaran or stinkpot. 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.
 

·
Master Mariner
Joined
·
8,675 Posts
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.
 

·
Registered
Joined
·
926 Posts
If you are starting from scratch, perhaps you could come up with something like the pivoting Volvo drive units. You could swing the stern around like there's no tomorrow.
 

·
Registered
Joined
·
59 Posts
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.
 

·
Registered
Joined
·
2,549 Posts
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.
 

·
Registered
Joined
·
4,812 Posts
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.
 

·
Registered
Joined
·
375 Posts
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.
 

·
Registered
Joined
·
2 Posts
Discussion Starter #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.
 

·
Registered
Joined
·
375 Posts
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.
 

·
Member
Joined
·
74 Posts
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.
 

·
Registered
Joined
·
5 Posts
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.
 

·
Registered
Joined
·
375 Posts
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.
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.
 

·
Registered
Joined
·
22,348 Posts
.....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.
This is exactly correct, in all respects. Unfortunately, that gap has not materially narrowed in decades. Manufacturing costs have come down dramatically, but it is going to take the energy density issue you've identified to really break through. Perhaps it could happen. We'll see. Of course, everything comes with consequences. Imagine the number of dead batteries that will litter the earth, if we don't get ahead of that curve too.
 

·
Registered
Joined
·
2,953 Posts
Are lithium batteries easily recyclable?

I know flooded lead batteries are almost completely recyclable. The nickel metal hydride batteries in my car can be completely recycled.
 

·
Registered
Joined
·
375 Posts
This is exactly correct, in all respects. Unfortunately, that gap has not materially narrowed in decades. Manufacturing costs have come down dramatically, but it is going to take the energy density issue you've identified to really break through. Perhaps it could happen. We'll see. Of course, everything comes with consequences. Imagine the number of dead batteries that will litter the earth, if we don't get ahead of that curve too.
Oh, there's a ton of room for improvement on all fronts. However, research on lithium and other novel chemistries has been going gangbusters since the cell phone, and now the electric car revolution started. I've seen at least 6 paths to 10-20x today's best power density being researched by major universities in the past few years.

I wouldn't say there hasn't been a big density breakthrough for decades, unless you're talking lead acid. Lithium batteries get more dense at a surprisingly linear ~7% per year. The big breakthrough has been production efficiencies. Tesla claims to be closing in on $100 per kWh. Considering that cost was $1000 per kWh 8 years ago, that's a pretty massive improvement. $100 is a big number, because at that point the powertrain of an electric car and the powertrain of an ICE car become even, meaning there's no longer a cost advantage to an ICE car. Case in point - the premium for the new generation hybrid Rav4 vs a gas Rav4 is now only $800 - and the hybrid is faster, more powerful, and gets considerably better gas mileage.

As Electric cars become more common, I think we'll continue to see better and better power densities. No idea how long it will take for production and density efficiencies to trickle down to boat world, though. Prices for marine lithium batteries are still in the $1000/kWh range.
 

·
Registered
Joined
·
22,348 Posts
.....I wouldn't say there hasn't been a big density breakthrough for decades, unless you're talking lead acid. Lithium batteries get more dense at a surprisingly linear ~7% per year.......
I think we agree. Lithium is not new technology. It too has been around for decades. Density has been increasing, but the 7% per year you note is going to take a long time to bridge the remaining 2000-3000% density gap. I think it will require an all new technology breakthrough, not just improvement of current battery tech.
 

·
Registered
Joined
·
375 Posts
I think we agree. Lithium is not new technology. It too has been around for decades. Density has been increasing, but the 7% per year you note is going to take a long time to bridge the remaining 2000-3000% density gap. I think it will require an all new technology breakthrough, not just improvement of current battery tech.
You're probably right. The current highest density I've read about so far in the Lion realm is 460wh/kg, or roughly double today's average, or about 10x lead-acid density. Graphene based batteries seem to have a lot of promise, too, for both reducing cost and weight.

There are a few other techs farther down the line if they can make it to commercialization. Princeton was working on a carbon nanofiber based tech that, in the lab, far outstripped any other tech yet developed.

Going in the opposite direction, I read about a professor who was working on a battery that fit inside of a container made out of incredibly cheap material, to the tune of about 2MWH per container. The idea was to use them for either powering battery electric trains or using them for grid-based applications where weight and size aren't important, but capacity and reliability is. A big, cheap, reliable battery would go a long way towards finishing off fossil-fuel based power.
 
1 - 20 of 62 Posts
Top