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Optimal propulsion system

11K views 77 replies 34 participants last post by  Brewgyver 
#1 ·
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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#3 ·
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.
 
#4 ·
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...
 
#5 ·
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.:)
 
#7 ·
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.
 
#11 ·
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.
 
#22 ·
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.
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.
 
#14 ·
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.
 
#15 ·
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.
 
#16 ·
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.
 
#19 ·
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.
 
#17 ·
"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.
 
#20 ·
"
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?
 
#18 ·
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.
 
#21 ·
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.
 
#24 ·
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.
 
#25 ·
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.
 
#28 ·
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.
 
#29 ·
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
 
#35 ·
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
 
#36 ·
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.
 
#38 · (Edited)
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.
 
#39 ·
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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