# Optimal propulsion system



## davidpm (Oct 22, 2007)

I have what may be a slightly unusual problem. My wife loves to sail but hates it when I have to put on the engine. I mean really hates it. She would rather sail at 2 to 3 knots than motor at 5 knots.

For coastal sailing however motoring seems to be a pretty common necessity.
The alternative is to get into a strange harbor after dark and miss dinner and a slip assignment.

I'm thinking that an optimal system might be an electric drive system with battery capacity for about 5 hours. This battery bank would be mated to a gen-set that had the horsepower to drive the boat at max throttle.

The system would be reasonably simple. 
Genset with charger connected to battery bank.
Batteries connected to electric motor.

During the day if the wind was light I could motor sail for a few hours. The motor would be so quiet no one would know. 
In the afternoon while we were off the boat I would run the genset to charge the batteries (The genset would be insulated so its running would not be noticed by any other boats)
If I really had to run the genset to run the motor it would be big enough to do the job and I would just have to deal with the noise.


I know this is not a cheap solution. Probably double what a re power would cost.
It is also pretty complicated with lots of controllers and electronic controls.
It will be somewhat inefficient converting gen-set horsepower to electric instead of shaft power. I'm hoping that the built in inefficiency will be off-set somewhat by the fact that the the gen-set can be set to the most efficient rpm as opposed to a shaft driven motor where the rpm is used control the boat speed.

Weather I would be willing to pay for and actually build such a systems is another question but assuming the above usage what do you think?


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## todd740 (Apr 18, 2012)

There are a couple boats with this already available. The hunter e33 has this as an option and a cruiser did a conversion on his older boat.

Here is a link to their blog:
biankablog.blogspot.com/2008/05/going-electric.html


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## asdf38 (Jul 7, 2010)

todd740 said:


> There are a couple boats with this already available. The hunter e33 has this as an option and a cruiser did a conversion on his older boat.
> 
> Here is a link to their blog:
> biankablog.blogspot.com/2008/05/going-electric.html


Neat link. It reinforces how complicated a diesel engine install it. I remember reading some thread and someone wrote off electric propulsion by saying it "wasn't suited for the marine environment"...as if a combustion engine with it's requisite, lubrication, cooling, starting, fuel , systems with their requisite secondary filters, cooling, charging, system are? I'd say moving parts arn't well suited for the marine environment and electric definitely has the advantage there. The only problem is the low amount of energy stored in batteries vs diesel fuel.



> It will be somewhat inefficient converting gen-set horsepower to electric instead of shaft power. I'm hoping that the built in inefficiency will be off-set somewhat by the fact that the the gen-set can be set to the most efficient rpm as opposed to a shaft driven motor where the rpm is used control the boat speed.


This was the line of thinking when the chevy volt was in development. Then at some point they snuck in a direct drive system because it just wasn't efficient enough. However the boat is clearly a different situation - many have generators anyway for example. So I'm interested to see how this thread goes.


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## Faster (Sep 13, 2005)

What you're proposing is gaining traction these days.. there are a few boats offering this kind of package, and you're right, it's not going to be inexpensive. Overall I think the electric drive will be best suited to the in-harbour/out of harbour needs of the daysailer, once you get into generators to power the electric power most of the advantages are lost. Getting enough solar to power up such a system will have its own challenges as well.

Good luck, btw, coming up with a powerful enough generator that no one else will notice running....

Emerging battery technology may well make this more feasible in the near future.. It's a neat idea...


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## davidpm (Oct 22, 2007)

Faster said:


> once you get into generators to power the electric power most of the advantages are lost. .


The way I see it all of the advantages are lost except one.

It's more expensive to install and run and more complicated and may be just as noisy.
If you typically sail 50% and motor 50% and catagorize a light electric assist in the sailing side then maybe you can sail 90% and motor 10%.

Lots of if's.
My wife really hates motoring under diesel.


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## davidpm (Oct 22, 2007)

Faster said:


> Good luck, btw, coming up with a powerful enough generator that no one else will notice running....
> 
> .


I saw a generator at the boat show that seemed very quiet.
Your right this is a key component.


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## asdf38 (Jul 7, 2010)

I hope for your sake an expert chimes in but I've been poking around looking at this this morning.

First a number to use as a reference is that a hp is 0.75kW. This means that if you want to run continuously with the equivalent of a 15hp diesel you need roughly 11kw available. Punching that into a search for generators seems to reveal some bad news - 11kw generators are huge. Panda for example is 265 lbs for just 6kW (The 6kW is electrical output so the conversion losses are already taken into account. I bet it's a 6-10hp engine). And although there are a lot of complexities I think that's a fair starting point. 

However it does seem like you have quite a lot of places to make compromises. First, assuming you're making a long passage and know it, you can charge the batteries ahead of time. Then you could run the generator and draw off the batteries at the same time and get good speed for a long time.

Second, even if you're limited to say 1/2 throttle average for a long passage that should still net 3/4 or 2/3 speed given the typical power curves. And you'll be able to throttle up for quick bursts anytime you want. Actually, you can probably specifiy a fairly oversized electric motor without a whole lot of extra cost/weight and have some pretty high speed burst potential. That's a neat option to have if you get into trouble.

If you're willing to comprise your passage ability by installing a smaller generator it might work well, if not it looks like it's heavy and expensive.


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## sww914 (Oct 25, 2008)

Earplugs and Valium would be cheaper! 
I'm interested in your projest.


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## cruisingdream (Feb 7, 2007)

here is a place to start
Vetus Electric Drive EP2200 - French Marine Motors Ltd
or D&D Motor Systems - Electric Boat Motors


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## Mobnets (Apr 24, 2011)

davidpm:
What kind of motor setup do y0u have now?
Mobnets
1973 Paceship Chance 32/28 "Westwind"


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## nickmerc (Nov 2, 2008)

I had been thinking about an electric option for my Pearson 30 for if/when the A4 dies. Electric motors are very efficient. With a timing belt reduction you have almost limitless combination for matching the ideal motor rpm to the ideal prop rpm. You will find numerous posts and articles expounding on the benefits of electric propulsion so I will not go into detail here. I will say that most of the claims are reasonable accurate. The one drawback (and it is a major one) is energy storage. Batteries are just not up to the task of replacing fossil fuels... yet. 

The serial hybrid approach is one way to bridge the gap at this time. While not ideal it is, in my opinion, a good stop measure. As battery technology improves the only change you will have to make is replacing the batteries and possibly the charging system.

You will have to determine if electric propulsion will work for your mission in the first place based on your distance and speed requirements. For me as a lake sailor it is a good fit. When I was on the Chesapeake Bay; not so much.

The reduction in complexity and the very small size of an electric motor required to power my boat to hull speed was remarkable. The largest expense was batteries. Both financial and physical space/weight.

As I look at daysailer to replace my keelboat (new mission requirements) I am 90% set on electric for aux propulsion.


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## ParadiseParrot (Oct 6, 2010)

The lighter the boat the better electric gets. You can cruise the flats fishing with a trolling motor for a long time.Keep us informed on how the project goes. Interesting subject.


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## denverd0n (Jun 20, 2008)

davidpm said:


> She would rather sail at 2 to 3 knots than motor at 5 knots.


Me too. So you adjust your expectations, don't set a schedule that has you going near hull-speed all the time, and enjoy life at a slower pace. Easy-peasy, and doesn't cost a penny.


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## davidpm (Oct 22, 2007)

denverd0n said:


> Me too. So you adjust your expectations, don't set a schedule that has you going near hull-speed all the time, and enjoy life at a slower pace. Easy-peasy, and doesn't cost a penny.


Actually for this investigation I'm expecting the following:
It will not be cheap
It will not be simple
I want to be able to go hull speed whenever and for as long as I want as long as long as I'm willing to run the diesel.
I want to go quietly for as long as the batteries hold up when the diesel is not on.

I'm pretty sure it is doable the real question is if I'm willing to pay for it in both time, money and complexity.


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## CapnBones (Sep 20, 2010)

Just an observation about battery capacity. I have a lot of interest in electric for cars and motorcycles, and the batteries are not where they need to be yet, true.

I am assuming a 30 ft sailboat:

For the space that you save by putting in an electric motor, and weight reduction, say 200lbs (based on an atomic 4 is about 350 w/fluids). How many 6v golf cart batteries could you wire in that space. I know with the size dimensions of my engine compartment I could probably rack 6 - 6v golf cart batteries @ 72lbs each 423lbs. So you gain about 200-250 lbs, of course now you don't have to carry fuel so subtract that weight and you aren't too much heavier. 
Now with that much power - 1560 amp hours @12v based on
http://www.trojanbattery.com/Products/T-1456V.aspx
and looking at the speed to distance assumptions of the Vetus mentioned earlier in this post, you could get quite a good distance for minimal weight addition. I have 150-200lb friends so I will bring one less and it is a wash haha.

Then it really all goes back to charging, and if you are not a long distance cruiser you can most likely do it right at the dock. With shore power and that setup you could even use a golf cart charger/charging system.

Additionally I am currently setting up 4 of those batteries as my house bank which has 2 huge 12v monsters of the same relative size, but only 200 AH total. so there is an additional reserve 520AH, optimally of course, but engine starting battery becomes obsolete and there is space for 2 more.


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## RNDROB (Sep 6, 2012)

Is the objection that fossil fuel is being burned or noise and vibration that is upsetting the peace and tranquility? IF it is the latter wouldn’t it also be prudent to look into ways to dampen the noise and vibration to a reasonable level? Some of the modern small diesel cars are very smooth and quiet. Case in point the VW TDI.


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## hellosailor (Apr 11, 2006)

"The hunter e33 has this as an option"
Only one problem, Hunter's parent company are now out of business, so you'd have to try finding a leftover or a used one.

I don't see generator noise as being as issue since one of David's criteria was "not missing a slip assignment" which means he can just _plug in_ and recharge at the end of the day.

Find a Chevy volt, gut the drivetrain and the very economical generator from it, and voila, the rest is just wrenching. Especially if you can plug in most nights to recharge.

Short of that, I'd wonder if new engine mounts (after 5 years they've stiffened up and make for a noisier shakier boat) a shaft isolator, balancing, and some engine bay insulation might not be the best ways to tackle this.


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## Jgbrown (Mar 26, 2012)

Silly idea perhaps, but what about an outboard motor on a bracket? Ugly perhaps, but not overly expensive in comparison. The 4 stroke ones are pretty amazingly quiet. Could use that most of the time, then fire up the big diesel if you really needed the power. That would probably be the most economical and simplest solution.


FWIW I think electric is a great idea overall, the power generation potential while under sail would seem to me to be a nice bonus too. The costs certainly aren't insignificant though, especially if you want to be able to move at hull speed for as long as you have fuel. If my Yanmar dies I may got that route.

It's the last idea that I don't really understand perhaps. What is your current fuel range at hull speed? If you could have enough batteries for even 50% of that range, and a generator that could charge your batteries at 50% of the consumption rate(5kw for example) you could get the same range as your current setup if needed, much easier than trying to have a generator that will produce 100% of the electric motor's requirements. Or 75% of the range on batteries at hull speed, with a generator that could produce 25% of your requirements... Which would get you almost to the Honda 2000 territory.


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## davidpm (Oct 22, 2007)

RNDROB said:


> Is the objection that fossil fuel is being burned or noise and vibration that is upsetting the peace and tranquility? IF it is the latter wouldn't it also be prudent to look into ways to dampen the noise and vibration to a reasonable level? Some of the modern small diesel cars are very smooth and quiet. Case in point the VW TDI.


That looks interesting but I saw only 300hp engines. Need a bigger boat.


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## davidpm (Oct 22, 2007)

hellosailor said:


> "
> Short of that, I'd wonder if new engine mounts (after 5 years they've stiffened up and make for a noisier shakier boat) a shaft isolator, balancing, and some engine bay insulation might not be the best ways to tackle this.


Has anyone done this? What was the result?


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## davidpm (Oct 22, 2007)

Jgbrown said:


> It's the last idea that I don't really understand perhaps. What is your current fuel range at hull speed? If you could have enough batteries for even 50% of that range,


That would be great but sadly is not going to happen. Most battery banks that folks are willing to pay and find room for have the fuel equivalent of less than a gallon.

The capacity of today's battery banks are amazingly low compared to fossil fuel.

In my scenario however with the usage of the boat being sailing for 3 to 6 hours then being off the boat for shore visits the charging can be done by either generator or shore power while we are off the boat.

I want the option for safety and itinerary flexibility to forget about battery limits (and our precious tranquility) and just motor for as long as our 30 gallons will take us.


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## sww914 (Oct 25, 2008)

nickmerc said:


> I had been thinking about an electric option for my Pearson 30 for if/when the A4 dies. Electric motors are very efficient. With a timing belt reduction you have almost limitless combination for matching the ideal motor rpm to the ideal prop rpm. You will find numerous posts and articles expounding on the benefits of electric propulsion so I will not go into detail here. I will say that most of the claims are reasonable accurate. The one drawback (and it is a major one) is energy storage. Batteries are just not up to the task of replacing fossil fuels... yet.
> 
> The serial hybrid approach is one way to bridge the gap at this time. While not ideal it is, in my opinion, a good stop measure. As battery technology improves the only change you will have to make is replacing the batteries and possibly the charging system.
> 
> ...


I read recently that the technology exists for much better batteries but that the oil companies own the patents. They didn't cite anything that actually proves that but it sounds plausible or even likely. If so, it's just sad.


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## davidpm (Oct 22, 2007)

denverd0n said:


> Me too. So you adjust your expectations, don't set a schedule that has you going near hull-speed all the time, and enjoy life at a slower pace. Easy-peasy, and doesn't cost a penny.


I agree in theory but in practice it does not work for me.
Very often here in Long Island sound it can be days before the 2 knot current, the wind, sunny weather and daylight and my days off all line up so all of the above are in our favor.
A simple 30 mile passage that can take only 5 hours can easily extend to over 10 hours. 
So we are left with two choices; wait all summer for a perfect day and maybe use the boat a couple times or go, with auxiliary power, and have a pretty good day.

Actually is it a lot worse than the simple choice above would suggest. The wind is so flukey that on the perfect day the wind will often die and on the marginal day the wind will fill. In either case you are committed to the trip and it is just not fun to bake for 10 hours and miss a shore dinner and not safe to try to dock in the dark.

So for the 90 percent of the days when I might just need a little boost for 4,5 hours it would be cool to fake it with electric and pretend we were sailing.

At the same time if I have to make a 300 mile passage I want to be able to do that too and keep good time and not be limited by batteries.


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## ShortCircuit (Jul 15, 2011)

Buddy of mine is halfway into a conversion from diesel to electric aboard his Aloha 32. He's going with Propulsion Marine's 5.5 kW solution. He's pretty pumped about the switchover; certainly the engine compartment has a lot more room without the engine and assorted plumbing. Batteries and a genset are part of the plan. More to come as events warrant.


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## P35juniper (Feb 11, 2010)

I've thought about a hybred system leaving the diesel in place then attatching an electric motor to the prop shaft with cog belt, I then could run just diesel, just electric, diesel with electric boost, diesel with recharge, 
I would use electric mostly for on/off mooring, docking then diesel for passage making if sailing was not possible. would try to have enough batteries for a few hours.

For my boat I was thinking a 10-12 hp electric DC motor in 48 volts, 8 six volt golf-cart batteries, that should give me 7 hp for an hour.


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## miatapaul (Dec 15, 2006)

sww914 said:


> I read recently that the technology exists for much better batteries but that the oil companies own the patents. They didn't cite anything that actually proves that but it sounds plausible or even likely. If so, it's just sad.


Yea, same thing happened to the 200 mpg carburetor in the 1970's! :laugher:laugher:laugher

Though I do find it difficult to believe that we cannot get a lot better millage from cars today. After all I got way over 50 MPG in my 1980 VW Diesel and it is more than 30 years later!


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## gbtillman (Jul 23, 2008)

Is something like this what you are looking for?

"www dot hybrid-marine.co.uk/5.html"

Beta Maring used to market it themselves but it looks like they have passed the marketing over to someone else. Also have one with a Yanmar.


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## hellosailor (Apr 11, 2006)

Fortunately those patents that the oil companies bought, were taken out in the 1930's. Yes, the conspiracy goes that far back and the good news is, the patents are due to run out soon!

Heard about a man in Florida who got on the news because the patent office sent his "maintenance" payment bill to Microsoft somehow instead of him, and now they wanted $2500 plus a $1600 late fee because he did't pay on time. What's the patent for? Wells, he's calls it a generator, and says once the battery starts it, the magnets in it makes enough power to keeps it running and supply more power, no more battery or other power source needed, and it can run your car or power a whole building in a blackout and hes just waiting for investors to back it.

Yessir, an electrical generator that needs a battery to start it, but then puts out power forever without any input or fuel. And he's actually GOT THE PATENT ON IT.

Dave, contact the man, you won't need that battery bank. And he's looking for investors.


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## Tallswede (Jul 18, 2012)

I'm sorry but there is no such thing as free energy. Even if the oil companies did own such patents, there would be so much money to be made from this technology that oil would be the least of their reasons to suppress it. There will always be a need for oil even if an energy source to replace it was found. There will allways be a need for lubes, plastics, and yes fuel derived from fossil fuel. If the technology existed, someone would have produced it anyway. China and others certainly do not recognize US patent laws. Just having a patent on an idea does not mean that it can be used in a real life setting either. So yeah, we may have a breakthrough sometime in the future, but I wouldn't hold my breath waiting for it. I like the ideas some have put forth around sound and vibration dampening. A good muffler design makes a big difference too. Most marine diesels I have seen are very crude and vibrate much more than need be. A good balancer system with a big heavy flywheel will go a long way toward making these small diesels more enjoyable to live with.

Kevin



hellosailor said:


> Fortunately those patents that the oil companies bought, were taken out in the 1930's. Yes, the conspiracy goes that far back and the good news is, the patents are due to run out soon!
> 
> Heard about a man in Florida who got on the news because the patent office sent his "maintenance" payment bill to Microsoft somehow instead of him, and now they wanted $2500 plus a $1600 late fee because he did't pay on time. What's the patent for? Wells, he's calls it a generator, and says once the battery starts it, the magnets in it makes enough power to keeps it running and supply more power, no more battery or other power source needed, and it can run your car or power a whole building in a blackout and hes just waiting for investors to back it.
> 
> ...


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## hellosailor (Apr 11, 2006)

"no such thing as free energy'

Swede, the oil companies have been putting out that myth for a hundred years, but now here's this fella got himself in the news, he's actually GOT THE PATENT FOR IT!

So, it must be true.


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## GufShoz (Dec 5, 2001)

Converted Hunter 29.5 & wouldn't go back.
Best source for good, expert info is:

Electric Seas


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## GufShoz (Dec 5, 2001)

David,
Sorry about the short post. I had a nice long one written, but because I tried to post a link, it wouldn't go on. If you have questions, send a personal message to me.
Amazing the passion of those who have opinions based on supposition.
Terry


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## asdf38 (Jul 7, 2010)

miatapaul said:


> Yea, same thing happened to the 200 mpg carburetor in the 1970's! :laugher:laugher:laugher
> 
> Though I do find it difficult to believe that we cannot get a lot better millage from cars today. After all I got way over 50 MPG in my 1980 VW Diesel and it is more than 30 years later!


It's not a lost art it's just no emissions laws, a tiny car and no horsepower.

If only we could pair today's engine technology with consumer expectations from the 70's we'd have 50+ MPG cars easily. Unfortunately it doesn't work. Even the most compact cars need 100+ horsepower (like my Fit) to sell.

As for the conspiracy theories I agree 100% with Tallswede. Oil companies have nothing to worry about meanwhile Apple is sitting on a hundred billion dollars and would love to spend a chunk of it on better batteries. Some things are just hard to do - storing energy in batteries is apparently one of them.


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## MattSplatt (Dec 10, 2010)

A good (though very in-depth - make a cuppa first) article discussing battery capacity can be found here:

http://physics.ucsd.edu/do-the-math/2012/08/battery-performance-deficit-disorder/

For those unfamiliar with his work, all of Tom's articles are excellent. He goes into the details and the actual real-life numbers of all kinds of energy systems.


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## Capt. Gary Randall (Jun 1, 2012)

Hello there, keep in mind that the Generators AC output changes with rpm in a very unfavorable way. Unfortunately changing rpm changes the AC volts, but most importantly hz. A modern generator needs to run at 1800 rpm's about 60 Hz. if you change the rpm you put the generator under undue strain, (windings in the stator) ( solid-state
voltage regulating system).Changing the RPM on a generator is very impractical. Whatever converts your AC to DC should operate at 60 Hz......Captg


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## hellosailor (Apr 11, 2006)

Paul-
"Though I do find it difficult to believe that we cannot get a lot better millage from cars today. After all I got way over 50 MPG in my 1980 VW Diesel and it is more than 30 years later! "
There ARE TDI engines that will getbetter mileage and poewr than your non-turbo-diesel got. The problem is, they are illegal on the US marlet because almost all diesels spew particulates and the EPA is convinced those are carcinogens that also cause allergy and respiratory problems. And it looks like the EPA is right on that one, more evidence keeps saying the same thing.
The EU has allowed them but starting "now" you will see all sorts of new diesels coming to market, most with an extra tank of urea which is injected into the exhaust in order to clean it up. I'd guess that will impact the boat market soon too.


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## Classic30 (Aug 29, 2007)

davidpm said:


> The way I see it all of the advantages are lost except one.
> 
> It's more expensive to install and run and more complicated and may be just as noisy.
> If you typically sail 50% and motor 50% and catagorize a light electric assist in the sailing side then maybe you can sail 90% and motor 10%.
> ...


Sorry I'm late to this party, but I thought I'd add my 2c worth based what I've seen - because it doesn't have to be that way:

First off, the system I've seen was: 11kW AC Gen set connected to battery charger and Danfoss Variable Speed Drive (VSD). VSD connected to ABB 3-phase AC electric motor. The batteries where connected into the VSD with automatic changeover to power the VSD off generator if it was running. All off-the-shelf stuff. This system has the following advantages:

1. The gen-set and batteries (as few or many as you want) can be mounted anywhere that's convenient weight-wise - not just in the tail of the boat, but generally somewhere central, under the saloon table for instance - and can be properly sound-proofed since there's no rotating shafts extending outside the box..
2. The gen-set provides AC power to other things in the boat (fridge, hot water, etc.)
3. The gen-set is compartmentalised: Engine-and-generator-in-a-bow. Removal for replacement or serious overhaul is four bolts.
4. The gen-set runs at constant speed, supplying whatever load the engine, batteries, etc. need. Continuous throttle and fwd/reverse is via the VSD.
5. The 3-phase AC electric motor is mounted low in the bilge and takes up hardly any room at all.

With this system, the generator automatically starts only when the batteries are getting low. The owners usually manually run the gen-set when anchoring (to make sure there is plenty of power for the anchor winch as well as the motor) and again during dinner to heat up the hot water for showers and run the microwave - very civilised!

Disadvantages: None I could see - apart from the cost, which may not be all that much more than a conventional set-up if you didn't mind having less batteries and hence running the gen-set more. The various bits do all take up space so it wouldn't suit a small monohull, but on a bigger boat - or a cat - it's ideal.


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## ParadiseParrot (Oct 6, 2010)

Well how these systems are put together by engineers is not a full hp generator but one much smaller that runs at best efficiency most of the time. If you need peak power you need to drain batteries.The electric motor is left freewheeling and becomes a generator while sailing to refill batteries.Genset would come on at preset drain point on batteries or by manual start.

The genset etc don't go in the bow.That effect trim to much.

There are several systems in place right now and some Charter cats have/are being produced. Look at there set up for ideas.

We all do different things in life to earn money. Go do that and leave system design to Electromechanical Enginneers. 

3 phase ac motors? VSD's? varispeed gensets? There is so much wrong here I won't even comment but if you PM me I will recommend a few books if your interested in the subject in some real way.


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## chucklesR (Sep 17, 2007)

The optimal propulsion system was put in place a thousand or more years ago and has been under continuous upgrade since - 
Sails 
Efficient, and getting better
Quiet
Longest range per unit of consumption. 

ParadiseParrot, not to offend, but it didn't take a electromechanical engineer to come up with that. I'm just a database guru and didn't even stay at a holiday inn last night.


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## chucklesR (Sep 17, 2007)

P.s., if you need backup - install a sweep oar and convert some sea biscuits to forward speed. 
I believe that propulsion system was designed by the guy / girl who built the garden of Eden.


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## davidpm (Oct 22, 2007)

OId Volvo


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## benjamen (Jun 21, 2012)

How feasible would it be to use an electic engine and batteries charged by solar cells? If your not using the motor that often it may have time to solar charge back to full between uses.


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## davidpm (Oct 22, 2007)

benjamen said:


> How feasible would it be to use an electic engine and batteries charged by solar cells? If your not using the motor that often it may have time to solar charge back to full between uses.


Their is a very active electric yachts yahoo forum where this has been discussed a great deal.

The consensus is that for most boats, even in light usage you would not have the room to fit enough panels to make that work.

Panels are used often to supply led lighting and to top off, the last 10 percent, charge all the time.
There was a showcase boat however recently that looked like an aircraft carrier, power only, that used only solar. It was a several million dollar experiment however.


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## smallboatlover (May 11, 2011)

What if you put a motor well in take out the desial. put a motor well in and use a 15hp or 20-25hp 4 stroke plenty of power and if it's in a well you won't hear it at all and will be good on gas, no noise. and will still keep the look of a inboard.


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## misfits (Dec 9, 2011)

There was an good article in Good Old Boat not to long ago about a guy from Maine that that did this very thing. I believe it cost him around 2K to do this. He only putted out of the harbor so he recharged the batteries during the week w/ a small solar panel. I think that any long range "motoring" would be impractical using electric. You'd have no juice left to power up the blender

The generator thing, what's up with that? If you're going to buy a generator to recharge the batteries, might as well just upgrade the motor & call it a day. Even the DC generators cost around 7K. 

For reasons that escape me, I always thought sail was the "optimal propulsion system"


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## Classic30 (Aug 29, 2007)

misfits said:


> The generator thing, what's up with that? If you're going to buy a generator to recharge the batteries, might as well just upgrade the motor & call it a day. Even the DC generators cost around 7K.


In case you missed reading the earlier posts, the biggest advantage (and one well worth the extra $$$ and effort) is that you can put the diesel generator anywhere you like - it doesn't *have* to be in the stern of the boat and in line with the prop.



misfits said:


> For reasons that escape me, I always thought sail was the "optimal propulsion system"


I don't think anyone here would disagree..


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## MedSailor (Mar 30, 2008)

David,

Your problem is a solved one. Up until now there were basically a bunch of startup electrical propulsion companies and there were DIY versions using floor waxer motors or golf cart motors (and batteries).

Now there is a mature looking system that has been picked up by Beta marine and Yanmar. I've emailed the designer of the engine/generator part and I've spoken with a salesman at Beta and the system seems really good.

Without getting into the whole diesel-vs-electric debate there are defiantly some good reasons to have a hybrid on a sailboat. Motor sailing is the main reason. You can be sailing along at 3 knots and with a silent push of the throttle you can now be going 5-6 knots and with very little amp hour expense. Personally, if I had the coin, I'd have one of these on my boat right now.

6 months ago when I contacted Beta and the motor designer you could get a brand new beta with the hybrid electric motor all set to go but Yanmar was not quite ready to ship. The electric motor could be bought by itself, or with a transmission, ready to mate to your existing engine (Volvo) shipped from the UK. I can dig up the prices and info if you like.

One nice thing about this engine is that you could also run the diesel engine without turning the prop, and it would turn the electric motor, creating a 10KW genset. So you had the option of running the diesel engine as you normally would for propulsion, running the diesel engine without turnint the prop and getting 10kw, turning the prop and using reserve HP to make electricity (up to 10kw) at the same time, or using the electric motor without the diesel engine as an electric drive. IT also had some nice features like an ability to sense when you were giving your engine near full throttle and it would automaticlally cut out the electric generator component to make sure you got full HP.

Here is the link:
Seagoing Hybrids - Hybrid Electric Marine Propulsion
For some reason the betamarine hybrid links are down today. Google shows them as an active link but it's not working today.

MedSailor


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## misfits (Dec 9, 2011)

Hartley18 said:


> In case you missed reading the earlier posts, the biggest advantage (and one well worth the extra $$$ and effort) is that you can put the diesel generator anywhere you like - it doesn't *have* to be in the stern of the boat and in line with the prop.


I cruised thru the thread. To have a propulsion system that doesn't make any noise is one thing. To go that route & then buy a diesel generator to recharge the batteries.....

Maybe it's just me but I have trouble wrapping my head around that one.


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## MedSailor (Mar 30, 2008)

misfits said:


> I cruised thru the thread. To have a propulsion system that doesn't make any noise is one thing. To go that route & then buy a diesel generator to recharge the batteries.....
> 
> Maybe it's just me but I have trouble wrapping my head around that one.


The idea is basically that you can propel at any time silently and you can later choose the time and place to make your noise.

I don't do a lot of motor-sailing because for me, once I fire up the (very loud) Perkins diesel, I figure I may as well go 6knots with it. The diesel likes the load and is most efficient on fuel at 80% of hull speed so when the sailing gets slow I take it all down and fire up the diesel.

If I had electric I could take 3knots of sailing speed and increase it silently to 5 or 6 knots without having to start up the motor, without the noise, without waiting for it to warm up, without disturbing the crew below etc etc. Later I could run the diesel to top up the batteries. In fact, the hour of maneuvering into the anchorage and setting the anchor would go a long way towards the amps used in increasing your speed under sail.

It's really not an efficiency thing, it's a peace and quiet thing and about enhancing your ability to sail. After all, if I wanted efficiency instead of peace and quiet out on the water I would have a power boat, or take the ferry.... Sailing itself is not efficient by cost, time, or any other measure....

Does that help?

MedSailor


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## misfits (Dec 9, 2011)

MedSailor said:


> Does that help? MedSailor


It does explain the thought process/reasoning behind it Med, thank you.

If it was time to repower & going electric was a viable option, I get that.

Coming from the power boat world, I never understood that whole motorsailing thing anyway. It kind of negates the whole reason for having a sailboat. But that's OK, it just knot for me


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## deltaten (Oct 10, 2012)

OK..This sounds like something I've been daydreaming about. I have a 15 Kw/55 amp propane 4 cyl Onan gen set. Total weigh w/o gas is #850. There is no out shaft, as the gen and motor are interconnected. I'd like ta see what it would take, motorwise??? .75 X 15 formula comes up to 11.25 hp. Size a boat to that hp and see if it could handle the weight of motor and gen set as ballast????? Figger mebbe 1200# with a couple batts and motor controller. If ya could mount the weight low enuff...........


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## hellosailor (Apr 11, 2006)

delta, propane has a very low energy density compared to diesel. Which is why ships and submarines and even locomotives use diesel-electric propulsion very successfully, but never use propane-electric. 

Propane will work if you can get it very frequently, very conveniently, very cheaply, and you've got lots of storage space. But unless you've got a rare boat operating n a rare environment, forget about it.


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## MedSailor (Mar 30, 2008)

How about a trimaran where the two amas are propane tanks??? 

MedSailor


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## hellosailor (Apr 11, 2006)

Won't work. You load down the amas, and that makes it harder to keep one out of the water at all times. Now you've got a tri-ma-barge instead of a trimaran.<G>


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## deltaten (Oct 10, 2012)

Hellosailor;
re: density/BTU; Yes, too true. The only advantage to propane is that it stores indefinitely. My musings were more about the drive-train issues and the other applications you mentioned. Since a freight train uses diesel to run gens to power electric motors; would the same reasons/logic/engineering apply? I suppose not,; as a sailboat does not need to shift hundreds of tons of weight.


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## JulieMor (Sep 5, 2011)

In the automotive world, Tesla seems to be on the cutting edge of battery technology. Their cars run about 300 miles before needing a charge and, if my memory serves me correctly, requires only an hour or so to recharge, maybe even less. And their cars are lightning fast! But their cars aren't cheap.

But how would the best battery technology we have today work in a marine environment, propelling a much heavier object through a much denser media? Would it reduce the load on the generator? Would it burn the batteries out? Would they need constant recharging? Maybe Tesla can answer that.

When I see what Tesla is doing, I have to ask myself why the major auto companies aren't doing the same thing. I think the Chevy Volt is only good for about 35 miles on battery power alone. Why don't the big three make a more expensive model that can compete with Tesla? We gotta get the Tesla guy to work on marine propulsion. He'd figure it out.


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## Stumble (Feb 2, 2012)

Julie,

Tesla is using lithium ion batteries last I looked. Figure an energy density on them of about 2% by weight compared to gas. So to replace a gallon of gas you would need roughly 325lbs of batteries. The Tesla battery pack weighs around 900lbs, so figure the energy equivalent of 3 gallons of diesel. And they aren't cheap, the battery pack which is good for a nominal 4 years cost roughly $36,000. So even assuming electricity is free it's going to cost you $8,500 a year in battery packs. 

At today's fuel prices you would have to be doing a lot of motoring to come anywhere close to justifying it from a cost advantage.


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## MedSailor (Mar 30, 2008)

Stumble said:


> Julie,
> 
> Tesla is using lithium ion batteries last I looked. Figure an energy density on them of about 2% by weight compared to gas. So to replace a gallon of gas you would need roughly 325lbs of batteries. The Tesla battery pack weighs around 900lbs, so figure the energy equivalent of 3 gallons of diesel. And they aren't cheap, the battery pack which is good for a nominal 4 years cost roughly $36,000. So even assuming electricity is free it's going to cost you $8,500 a year in battery packs.
> 
> At today's fuel prices you would have to be doing a lot of motoring to come anywhere close to justifying it from a cost advantage.


To you good sir, I concede that you win this argument, and you will win for a LONG time to come. This isn't about just energy density and cost though. The cheapest way to get from point A to B on the water is by ferry. Next best, is powerboat. We can't possibly justify all the design and space losses of our sailboat hulls, the weight of our keels, and the massive expense of our rigs and sails compared with a simple small engine that can push us at displacement speed.

In fact, most of us already have that engine aboard but prefer to use our cost-ineffective method of propulsion (sails) even though they usually make us go slower, we can't pick our direction and they require constant attention. Curious isn't it? We crazy sailor types must like things in our propulsion systems besides cost and efficiency then. See my post a page back or so on motor-sailing and why we like electric.

MedSailor


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## hellosailor (Apr 11, 2006)

"We gotta get the Tesla guy to work on marine propulsion. He'd figure it out. "
Someone hasn't read up on what the Tesla cars are. It would be very easy to build a boat the same way. Make it a two seater, tack an extra fifty grand on the price to cover the battery system, and Bob's your uncle.

There's no magic in the Tesla cars, just a lot of EXPENSIVE stuff.

They were supposed to be partnering with Toyota for the RAV4 EV this year, but Toyota has also made some major quite announcement about getting out of the EV market (except for a handful of pre-committed cars as a test) completely now. They see it as being totally uneconomical.

Got a boat? Get a diesel, Mr. Herr Professor Doktor whatever Diesel designed them to run on peanut oil, not petroleum products. Of course, he had no idea the particulates in the exhaust would cause asthma and cancers, but the fuel (vegetable oil, unprocessed) is certainly cheap enough.


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## Familycruisers (Dec 15, 2011)

Lithium, on a boat, now that's a great idea!


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## Barquito (Dec 5, 2007)

OK, this is going to sound stupid: If noise and vibration are the issue; what about changing to an Atomic 4. My A4 is very smooth and quiet. If it happened that your diesel died, it would probably be cheaper to re-power with a rebuilt A4 than another diesel. Gas doesn't have the range of diesel, but, you are not crossing oceans. Just a thought.


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## asdf38 (Jul 7, 2010)

hellosailor said:


> "We gotta get the Tesla guy to work on marine propulsion. He'd figure it out. "
> Someone hasn't read up on what the Tesla cars are. It would be very easy to build a boat the same way. Make it a two seater, tack an extra fifty grand on the price to cover the battery system, and Bob's your uncle.
> 
> There's no magic in the Tesla cars, just a lot of EXPENSIVE stuff.
> ...


Right. The high-end sports car is ideal for electric in many ways. The car itself can be tiny so the batteries are practically carrying nothing but themselves and it benefits from the incredibly high low-end torque of electric motors. Plus it's expensive. Tesla was smart going in that direction but none-the-less I think the company still had a lot of close calls. Designing that car still wasn't easy.

As for boats, what I'd love to see someone try is to properly design in batteries as balast. An encapsulated full keel has lots of potential space if a boat builder designed it from the outset to hold batteries with a robust rack system.

If you could stack them 2 or 3 layers deep that could be significant capacity and since it's replacing ballast anyway there would be little penalty - the main one being the lower weight density of batteries compared to lead (you could still have lead at the bottom). The challenge would be to make it safe and serviceable.


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## Stumble (Feb 2, 2012)

Asdf,

Again we get to an energy density problem. Lets assume that we design a keel so that the entire mass is one big battery. And let's assume that the design will keep the same density as raw lead (we know this isn't true, but it makes the math easier). 

Taking a Beneteau 31 for our comparison (because they use iron keels, so the density might be closer to correct) 

1) the 31 carries 2,200lbs in ballast.
2) lead batteries have an energy density roughly equal to 1/650 of diesel.
3) converting the entire mass of the ballast gives the same energy potential as about 4 gallons of diesel.

So we suspend a huge amount of money designing the battery pack, figuring out the electrical issues, have a relatively short lifespan for the ballast, ect... And still only have 1/10th the motoring range of a comperable Diesel engine. But we can't carry jerry cans to full up on route. If we run out of power, we either have to find a marine with power, or be able to generate power on board. 

So if we want to reasonably extend the range, we have to put a pretty large generator on board, which is going to require adding back the fuel tanks, thru-hulls, ect that we avoided with the electric drive in the first place. How big of a generator? Figure 15kw would be sized to the engine.

Rit now there just isn't a storage device anywhere close to the same density of diesel. For all it's problems, fossil fuels are insainly energy dense compared to anything else we have come up with, and while battery technology is getting better, there isn't anything on the drawing board that even comes close to fossil fuels.

So how much do batteries need to improve?

Diesel.......................45.4. Mj/kg
Gunpowder.................3.0
Lithium ion batteries ...0.72
Lead acid battery........0.1


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## asdf38 (Jul 7, 2010)

Stumble, I'd like to spend more time running the numbers because this scenario, replacing balast with batteries, is as good as it's going to get for electric boats. But a couple things jump out quickly. 

Are you factoring in conversion losses? Diesel engines have an efficiency of about 45% and Electric motors are >70% (70-99.99 apparently) based on some quick googling. So that close to doubles your 4 gallons to 8. 

Second, 2200lbs? My Contessa has more ballast than that. However I'm not saying 100% of balast should be replaced but many boats that size have far more. 

And really, if we're talking 8 gallons of gas that's a lot. I've gone 2 seasons on less, at the least that's a significant passage even for a large boat.


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## davidpm (Oct 22, 2007)

Stumble said:


> Asdf,
> 
> Again we get to an energy density problem. Lets assume that we design a keel so that the entire mass is one big battery. And let's assume that the design will keep the same density as raw lead (we know this isn't true, but it makes the math easier).


Some may a drifted this thread a bit but the original proposition was diesel / electric hybrid.
So we are talking about the energy density of diesel.

The trade offs are that it will cost more as you need more equipment.

It will not be as efficient as their are conversion losses but maybe not as much as might be at first supposed due to being able to run the diesel at optimal rpm and run the electric with optimal torque.

The only advantage, and for some of us it might be worth the extra money, is the quality of life advantage. IE for most passages you may not need to run the diesel at all but if you have to you can.

Also you possibly get the advantages of a genset without a separate diesel for that purpose.


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## Classic30 (Aug 29, 2007)

Stumble said:


> So if we want to reasonably extend the range, we have to put a pretty large generator on board, which is going to require adding back the fuel tanks, thru-hulls, ect that we avoided with the electric drive in the first place. How big of a generator? Figure 15kw would be sized to the engine.


If you were referring to installation in a power cruiser, you might be right.. but for a yacht that's not actually true. For a hybrid installation on your average Bene 31 (generator/batteries/electric motor) the generator could be 2/3-3/4 the size of the electric motor depending upon the sort of cruising you do.

No-one has ever suggested you could do away without fuel tanks, thru-hulls, etc. (you still need the thru hulls for cooling most electric drives anyway) but it's easy to forget that, either under sail or on the hook without the motor running, a 10kW generator is going to recharge the batteries mighty quickly! ..and give you plenty of AC power (enough to run a small house!) whenever you want it.


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## deltaten (Oct 10, 2012)

" a 10kW generator is going to recharge the batteries mighty quickly! ..and give you plenty of AC power (enough to run a small house!) whenever you want it. "

Yep! 
I could run the whole (little) marina on mine!
I don;t remember the name; but there's some kinda motor controller that lets ya run from 0 rpm up to max without loss of torque. "Variac" comes to mind; but I could be disremembering?! 


OK.. new twist....
What about air cooled engines??
I got's an old 2 cyl Honda 350 that would be a willing donor!!!!!!


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## Classic30 (Aug 29, 2007)

deltaten said:


> I don;t remember the name; but there's some kinda motor controller that lets ya run from 0 rpm up to max without loss of torque. "Variac" comes to mind; but I could be disremembering?!


They're called "variable speed drives" or "VVVF motor controllers" or (whatever else they can think of) in industry. There are a host of manufacturers out there: Toshiba, Mitsubishi, ABB and Danfoss being the most common for marine use. Now cheap and off-the-shelf..



deltaten said:


> OK.. new twist....
> What about air cooled engines??
> I got's an old 2 cyl Honda 350 that would be a willing donor!!!!!!


Too noisy. You need to get air in to cool it (obviously) and that means plenty of holes to let the noise out. There's plenty of nice cool water in the ocean that does a better job.


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## Stumble (Feb 2, 2012)

Asdf,

Those numbers are what I remember from an engineer on another forum. I believe he calculated in conversion efficiency, but I could be wrong. But don't forget you also have to calculate in the usable energy portion. Lead acid batteries can only reliably use about 50% of their nominal power, without damaging the cells lifespan.

Hartley, 

I actually think diesel/electric is a reasonable way to go. At least under some conditions. 

1) there is or needs to be a generator anyway
2) reduced power range is acceptable
3) the size of the house loads correlate reasonably to the propulsion demands (we don't want a 20kw generator running to power one AC)
4) little or no range expected from the batteries
5) propulsion requirements are minimal

In short I think it is possible, but doesn't meet many boats requirements since 3 and 5 are conflicting. The conversion is roughly 1hp=.75kw. So if your boat has a 20hp engine, you would need a 15kw generator to have the same power available at the throttle (ignoring conversion inefficiency). If you have a 40hp engine, which is pretty common on 40is footers you would be in the 30kw range. 

Frankly I don't know of many boats that would install a fraction of this size generator for house loads. And it would be massively inefficient to operate it just for house loads. Even if you were willing to sacrifice some available power you would have to make a pretty massive reduction in available power.


The only way electric power is if you can accept a pretty minimal range. Like just in and out of a harbor. For many day sailors this would work fine. But you would also loose the capability to make longer trips under power. I for instance would be fine with this system 99% of the time, but for a week or so a year we take the boat about 100 miles away for a distance race. I don't know that I would be willing to give up the capability to do this even if the rest of the time electric power would be fine.


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## Classic30 (Aug 29, 2007)

Stumble said:


> Hartley,
> 
> I actually think diesel/electric is a reasonable way to go. At least under some conditions.
> 
> ...


First off, I've seen these systems in operation on motor cruisers (with large beer fridges!) and they certainly work and work very well - providing the added advantage of very short range propulsion to get to to anchor or out of the way should you happen to run out of fuel (don't ask!).

Your numbers seem about right to me - you'd have to expect that the diesel geneator would be about one or two sizes smaller than the diesel you pulled out. Don't forget that the generator control system will run the generator at it's optimum speed constantly regardless of boat-speed - there's no need for the "peak power/extra revs" capacity you might normally have with a diesel installation because that can be supplied better by the batteries.



Stumble said:


> The only way electric power is if you can accept a pretty minimal range. Like just in and out of a harbor. For many day sailors this would work fine. But you would also loose the capability to make longer trips under power. I for instance would be fine with this system 99% of the time, but for a week or so a year we take the boat about 100 miles away for a distance race. I don't know that I would be willing to give up the capability to do this even if the rest of the time electric power would be fine.


Not necessarily. One thing is for sure, as your list indicates: The power system and *all* components need to be correctly selected, designed, installed and commissioned by an experienced electrical engineer so that everything works together properly to meets the needs of a particular boat+owner - a diesel hybrid isn't something your average Joe Boatie (or even his regular Marine Mechanic) can put together without something going horribly wrong.

At the end of the day, similar to the diesel-hybrid system in a car, a diesel-hybrid system in a boat will cost more than a straight diesel but will also have a few advantages to make up for the added cost - depending entirely upon the selected installation and the way it's used.

Just imagine using thrusters instead of a conventional propeller/shaft? Or water jet?? For the first time since the propeller was invented, stern glands are no longer an essential part! With a hybrid system the possibilities are endless..

But for most people, in most places, with technology as it stands now, a hybrid is simply too complex to be worth the added cost/benefits - but that doesn't mean that, just like hybrid cars, it isn't the way of the future.


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## Brewgyver (Dec 31, 2011)

sww914 said:


> I read recently that the technology exists for much better batteries but that the oil companies own the patents. They didn't cite anything that actually proves that but it sounds plausible or even likely. If so, it's just sad.


Yeah, just another conspiracy theory, and total BS. If such technology existed our military would be using it, and they're not.

The fact is, higher tech batteries DO exist, and can be made/bundled with the ampacity for such application. They're just prohibitively expensive. You probably have one on your person.


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## asdf38 (Jul 7, 2010)

Ok I wanted to run some numbers and see how things looked in more detail. Hopefully I don't make a mistake.

Diesel fuel is listed at 45MJ/kilogram which is 20.45MJ/lb or 36MJ/liter.

A Group 27 from Deka weighs 53 lbs and has 90Ah. This is 90Ah*12V=1080Wh.
A joule is a Watt-Second so 1080*3600 (seconds per hour) is 3.888MJ.
So per pound this is 3.888MJ/53lbs = 73kJ /lb
or by volume it's 3.888MJ/13 liters = 0.3MJ/l

This puts diesel at 280X as dense as the lead acid by weight or 120X as dense by volume. Or another way, one Group 27 is 0.0285306 gallons..

So to compare this to the example from earlier 2200lbs gets you 42 batteries which nets about 1.2 gallons...

As pointed out earler this gets better (by about 75%) when factoring in conversion efficiency (electric is more efficient than diesel) but then worse (by a factor of about 2) when you figure usable capacity of a bank.

Man that is pretty bleak for electric. Lithium is several times more dense than lead acid, at least about 5x according to some quick numbers but that's still not too good.

My only last thought is that the 45% number for the desel engine seems a bit high, perhaps that number is a train engine or a power plant operating at optimum RPM? What's a small boat engine get when running at 1/2 or 2/3 throttle?

http://www.dekabatteries.com/assets/base/0194.pdf


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## Classic30 (Aug 29, 2007)

asdf38 said:


> My only last thought is that the 45% number for the desel engine seems a bit high, perhaps that number is a train engine or a power plant operating at optimum RPM? What's a small boat engine get when running at 1/2 or 2/3 throttle?


Train engines tend to be diesel-electric (i.e. Hybrid minus the batteries) and this would also have some benefit on a yacht - a bigger one at any rate.. There are a few ocean racing yachts still around from the 70's and 80's that used hydraulic drives for all the same reasons.

The figures are beyond me, but I'm not sure you're comparing apples with apples..:

1. A diesel engine in a boat gets throttled anywhere from idle to 100% with different fuel consumption at each throttle setting ("efficiency" if you like - at some throttle setting it will be "most efficient", but Murphy's Law states that max efficiency won't occur at cruising rpm..  )

2. A diesel generator in a marine Hybrid installation runs at "max efficiency" all the time i.e. the ECM selects the optimum diesel engine speed to match the load, which will be either (a) running the motor or (b) charging the batteries or (c) both.

This means that, in terms of "fuel efficiency"/"energy consumption"/whatever, the Hybrid will be far more fuel efficient under nearly all conditions than a straight diesel engine - offset by the cost of the batteries, etc, etc.

If you take a Hybrid car for a spin, you'll quickly see how it works..


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## MedSailor (Mar 30, 2008)

One problem with all these energy density numbers is that they only show how a boat would use the electric motor ONLY or the diesel engine ONLY and compare them. Many of the advantaged to a hybrid, or even pure electric involve ways that you can use then engine _other than motoring along at hull speed from point a to point b_.

I think pure electric systems could be very practical for small boats who sail well and only use their engines to get in and out of harbor anyway. I've been on many a T-bird that departed the dock with only a gallon or two of gas. Pure electric wouldn't be much different.

But pure electric isn't for most. And it's applications are varied and it's merits many. Part of this though is you have to imagine how you would use it _differently_ to your regular propulsion system. Personally I would kill for the ability to have a hybrid system such as the beta marine system I listed at the beginning of this thread. The advantages for me with just a very modest battery band would be the following:

1: I could add several knots of speed to my light air sailing with very few amps used. This would mean much more sailing and less time with the diesel on instead.

2: If the diesel died, I could motor right up to the breakwater of my marina and use my small battery bank to drive her in to the slip using pure electric.

3: More torque at low speeds means better handling in close quarters.

4: I would have a huge genset (not that I really need it)

5: Regenerative power while sailing at hull speed.

and all this could be done with your regular, or slightly enlarged, house bank. No need to replace your keel with lead acid batteries or spend 20L on Lithium ion batteries. What this system would not do is be the only force driving me long distances. For that, I have my diesel engine, and these funny triangular white things....

The link below outlines the pros and cons of how a hybrid system (of sorts- actually its a pure electric and an outboard) can be used in many different ways. Here is an excerpt from the link below:
Epods in Use

_3. Light wind sailing was a pleasure for once. Typically the Gemini is not great in light winds due to her low aspect sail plan and small control surfaces ineffectiveness at slow speeds. However with the e-pods providing just a little push (5 amps) the boat was able to create its own wind to keep the sails pulling and the boat moving. The e-pods providing enough water flow over the rudders to allow you to steer. We sailed past the bow of a 40 foot mono who was hardly moving at maybe 1 knot mostly due to the tide; they were greatly impressed with our speed under sail; they had no idea there was anything helping us along as the outboard was clearly off and up out of the water at the time. With only a breath of wind she was doing between 2-3 knots; just enough to keep me from resorting to the outboard. Keep in mind that this was with 14 people aboard so the boat was heavy and we had been expecting normal heavy summer winds and thus were using the small 100% heavy working jib and full mainsail; not at all the right setup for light winds so the speed was even more impressive given these facts. I am definitely more likely to sail more or should I say motor-sail with the e-pods._

MedSailor


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## Classic30 (Aug 29, 2007)

Those e-pods look cool!

I agree with all that, except this might need some tossing around:



MedSailor said:


> 5: Regenerative power while sailing at hull speed.


There are indeed a few "towable generators" on the market, but I'm not sure how well using your normal drive propellor to regenerate actually works in practice - since I'm led to believe different shaped blades are required for generating power from the water flowing over them without creating too much drag in the process.

I'd think you'd be better advised to stick with a folding/feathering prop and use wind/solar generation instead... Just my 2c worth.


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## deltaten (Oct 10, 2012)

I wonder how much drag would be introduced by one of those 'drop-in the stream' hydro-gens? IIRC, they produce some tremendous amounts of power without costing huge dollars or taking up a lot of space.

A couple of fins ta stabilize and a tow cable added to the wiring set and just throw it over the stern!  Nah! Mebbe a faired stem and clamp arrangement to lower it off the stern quarter?

Would it be worth it to have the amperage vs the loss of a few tenths of a knot in cruising speed?

OK.. I see Aquair has that towed thang down already  Howzabout a MInn-Kota trailed over the side and reversed to generate??


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## Stumble (Feb 2, 2012)

The problem with towed and shaft generators is they require a boat that can maintain high average speeds thru the water over long periods of time. Most of these generators require a boat speed of 5kn to start working and only become really powerful past 6. That doesn't sound that bad, but they will also cost you roughly 1/2 a kn of speed while operating.

So unless you are consistently cranking out 130+ days you just aren't going fast enough to use them. And while I know many cruisers have hit that mark once or twice, not many can do it day after day reliably enough to count on them for power generation.


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## Brewgyver (Dec 31, 2011)

deltaten said:


> I wonder how much drag would be introduced by one of those 'drop-in the stream' hydro-gens? IIRC, they produce some tremendous amounts of power without costing huge dollars or taking up a lot of space.


They produce very little power, typically 100 watts, and that's at 7.8 knotts through the water, which is more than hull speed for a typical cruising sailboat. A more realistic 5 knotts, the output is down to about 50 watts - you can get that from a single solar panel.

With the micro-hydro, it would take several days of continuous operation to recharge the batteries from the use of an electric drive for an hour.


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