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  #61  
Old 10-16-2012
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Re: Optimal propulsion system

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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  #62  
Old 10-16-2012
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Re: Optimal propulsion system

Quote:
Originally Posted by hellosailor View Post
"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.
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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Old 10-16-2012
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Re: Optimal propulsion system

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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  #64  
Old 10-16-2012
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Re: Optimal propulsion system

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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Re: Optimal propulsion system

Quote:
Originally Posted by Stumble View Post
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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Old 10-16-2012
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Re: Optimal propulsion system

Quote:
Originally Posted by Stumble View Post
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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Last edited by Classic30; 10-16-2012 at 06:20 PM.
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Old 10-16-2012
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Re: Optimal propulsion system

" 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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  #68  
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Re: Optimal propulsion system

Quote:
Originally Posted by deltaten View Post
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..

Quote:
Originally Posted by deltaten View Post
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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Last edited by Classic30; 10-16-2012 at 07:34 PM.
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Old 10-17-2012
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Re: Optimal propulsion system

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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  #70  
Old 10-17-2012
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Re: Optimal propulsion system

Quote:
Originally Posted by Stumble View Post
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.
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.

Quote:
Originally Posted by Stumble View Post
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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Last edited by Classic30; 10-17-2012 at 03:45 AM.
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