Sailboat Power systems

[kloudie1]

Check out the short article in “SAIL” magazine by Nigel Calder. He is doing some testing with conventional diesel and electric and hybrid power systems.. got a grant from the Internation Council of Marine Industry Associations for the huge amount of money that will be required.. This month is just a beginning talking about what they are going to do and how.. Should be an interesting series of articles. Here is a web site: http://www.electricmarinepropulsion.org/Pages/NewsFrom_EU-HYMAR.html It should be interesting to see the economic breakdown of the costs..

 

[Bill Roosa]

My engineer senses tells me...

The energy density of lead acid batteries is low compaired to fossle fuels. Since you need a genset for recharging the batts and running the motor for safety reasons, you are really just installing a fairly large and VERY heavy electrical storage tank in addition to the fossle fuel one you already have.

Regeneration while under sail, solar.....Yea, yea, I get it. But I'm not sure you can sell it to the general public and make some money. Which is the whole point of the effort.

Now if they would consider 0-point energy they might make some progress

 

[Ross]

Re: My engineer senses tells me...

Traveling requires energy and the most efficient way to get it is with a sail. My sail weighs about 35 pounds and will push my boat at 6 knots all the way around the world. My diesel engine weighs about 350 pounds and the fuel for it weighs about 75 pounds and will push my boat at about 4.5 knots for about 1/100 th of the way around the world before I must replenish the fuel. The engine does come in very handy when I am approaching a dock.

 

[kloudie1]

Yeah, the forum beat this horse a good bit recently.. I think I made the point about energy density in the last go’round.. I find this interesting because it should show with pretty fair accuracy that if ya never want to motor more than about 4 hours, and almost all your motoring is a short in and out of the harbor, then a hybrid or in some very short cases, a plug-in pure electric is the most efficient (probably not most cost effective) solution to auxiliary power. Any time ya have to run a diesel to charge a battery for propulsion instead of using the diesel for direct propulsion, you are losing in the efficiency game.. (talking same horsepower) .. It is interesting to me that most tests use a considerably less powerful electric motor.. Seems that if a person would be happy with the smaller power, a smaller power diesel should be the comparison.. Nigel is using a good bit smaller electric motor than the diesel direct driver that they are comparing to. An interesting part of the study is in testing a few different types of propellers and maybe finding one that is a good compromise between pushing the boat and driving a generator when under sail.. Those really require two different blade shapes for best efficiency. Anyway, I found it to be an interesting project .. most of what they are doing could be cheaply and quickly done by math models and the stated performance curves of the various motors and generators and wiring systems.. but the propeller testing is a lot more difficult to model. The test bears watching, I think !

 

[kenn]

I hear all the points about the low energy density of lead-acid batteries, but that's somewhat irrelevent to the viability of hybrid drives, because with a genset on board, you're NOT relying on battery storage for electricity to drive the propulsion motors. The battery bank need only be large enough to start the genny, or provide several minutes of manuevring power, or to run some electronics for a few hours or the weekend.

As with diesel locomotives, the generator drives the electric motors directly when extended running is required.

Potential advantages of hybrid systems:
- better weight distribution - electric propulsion motors are lighter than equivalent combustion motors, and the genset can be located anywhere in the boat
- potential for efficiency - electric motors are more efficient across a wider range of power output; generators need only run in their most efficient band when generating.
- better redundancy - instead of having both an aux motor and a generator, a boat can carry two generators
- regeneration - the propulsion motor can function as a generator when sailing. It's not as efficient as a dedicated wind or water generator, but it's something.

Now... it's still a question whether the modest propulsion requirements of most sailboats are economically met with hybrid systems today, but I have absolutely no doubt that we will be there in maybe 20 years or so, give or take an oil crisis. Of course, more efficient battery technology will also drive this.

 

[Ross]

The primary reason for diesel electric drive systems on trains is because electric motors can generate torque at zero rpm. Steam can also do this but General Electric won that contest many years ago. We don't need the benefit of very low speed or no speed torque because water allows for slip.

 

[kenn]

The primary reason for diesel electric drive systems on trains is because electric motors can generate torque at zero rpm. Steam can also do this but General Electric won that contest many years ago. We don't need the benefit of very low speed or no speed torque because water allows for slip.

For diesel locomotives, there's also the fact that electric motors fit into the form-factor of a standard-height truck (train wheelset), and that the prime mover (generator) gets to run in it's powerband, and that it's much much much easier to change field taps than it is to shift mechanical gears. Oh, and dynamic braking, too. But we digress.

 

[dvideohd]

other technologies....

There are some other technologies out there...

If you have big heavy boat...... Lead's good.. My keel is Lead....

************

Suppose you have that "light boat" though.....

A tandem Stitch and Glue Kayak can weigh about 68#. With sail and outriggers, add another 30-40". So a light, 21-25' boat there is less than 100#.

to drive it, I might want a 12V system -- but more likely a 24, 36, or 48V motor... Obviously, a bit of research in MinnKota's data sheets would help.....

To power, I might want a LiFePO4 battery system - the same kind that would power an electric bike or perhaps a light electric car...

So thinking along these lines, you say "starting with a minimum amount weight and working up... what would you really need?

A BIG LiFePO4 battery system is a good bit of change... but it really has the right stuff for light weight....

********************************

Rather than thinking "top down" - ie, traditional power/motors, it is also a good idea to think "bottom up" - ie, least weight - most efficiency - and then relax the components as you can to fit the boat you have.....

************

I have this nifty 25hp Electric Motor for aircraft applications - 440HZ, and rotates VERY FAST... not sure what to do with it yet... but with a good gear box - it would be very happy on the boat... It's very small... Would need some seriously clever power system work.. but I can see it... It's not DC, either....

--jr

 

[Ross]

There are some other technologies out there...

If you have big heavy boat...... Lead's good.. My keel is Lead....

************

Suppose you have that "light boat" though.....

A tandem Stitch and Glue Kayak can weigh about 68#. With sail and outriggers, add another 30-40". So a light, 21-25' boat there is less than 100#.

For that a paddle is good.

 

[dvideohd]

you could also say...

absolutely right...

Paddles are good...

So with that tandem kayak - we have to paddelers.... :>

and we can have the sail..... :>

It's just sheer tinkering to think about the motor... but I seem to zero in on thinking of the last, annoying 1" of bad weather...

*******************

But you are right... Best thing is two good paddles, a compass, and bring #2 son to paddle while I look at the compass....

-jerry

 

[Bill Roosa]

How to gain efficiency

A great way to not do it is diesel engine--electric generator--electric motor--gearbox--prop. Mr. Carnot determined that the best we are going to get out of that diesel engine converting fuel to work is ~25%. Electric generators and motors are pretty efficient by comparison at ~85% and gear boxes are super efficient at 98%. Props are only about 50% efficient at converting all that work to forward thrust. From an engineers viewpoint I'd attack the problem as follows:
Diesel engines are stuck at 25% max (laws of physics) forget getting improvements here look for better ways of converting (>25%) diesel to useful work.
motor generator sets are just being used because we think we can increase the efficiency of a diesel by running it in it's best power band (yawn 23-25% is not much to write home about) so I'm not really interested in going that way unless there is a reason as it just adds more complexity, cost, reduces efficiency by adding in an additional conversion of energy from one form to another.
Gearboxes are the way to go IF we need to adapt our diesel to useful work conversion device to a different speed. Not sure we need to at this point.
Props are really bad at what they do. Surly we can do better than 50%.

So trash the diesel (any internal combustion engine really) as a fuel to useful work conversion device. Fuel cells to turn diesel directly at a conversion rate of >25% would show an immediate improvement as you could dump the genset from the equation. Sterling engines working at higher temperature differentials would show a slight increase but they are still tied to the Carnot heat engine problem so I'm thinking that is not the way to go, however they are external combustion so they can use a multitude of fuels which perhaps would be CHEAPER or give more flexibility to the captain when he fuels up.
Magnohydrodynamic drives to replace the prop would seem to be the only way to increase the efficiency of useful work to thrust. I note that water is a polar molecule so perhaps there is some way to grab it electrically and accelerate it directly with out using a rotating device.

to sum up
IC engine(out of power band)--gearbox--prop
23%x98%x50%=11.27%

IC (in power band)--gearbox--prop
25%x98%x50%=12.25% Wow big increase

IC--gen-elect motor--prop
25%x85%x85%x50%=9.0% not headed in the right direction!!!

External combustion--gearbox--prop
32%x98%x50%=15.7% yep looks like fuel to useful work conversion is the culprit

fuel cell (guessing here but you get the picture)--motor--prop
30%x85%x50%=12.7% more wow

fuel cell--magnohydrodynamical drive
30%x65%=19.5%

The numbers (even very optimistic ones) tell me the fuel to useful work conversion and the rotational motion to thrust conversion are where we are having problems. Everything else is treating the symptoms from our decision to use IC and prop.

Regeneration with prop ties us to prop and a 50% loss in both directions or a 25% conversion of "free energy" to reusable energy. Great since it is free but we are not taking about driving the boat with sail, already know how to do that pretty efficiently. We are talking about driving the boat with motive power. That means we have to store the free energy which introduces the battery and low power storage density...... already discussed. So if you go down that route then you need better ways of storing and collecting (not a prop) the free energy. Since we can't store it as motion..... hey can we use flywheels... we are stuck storing it as something--electrochemical, atomic, mechanical, biological (open to suggestions here)... best solution is batteries or "super capacitors".

 

[kenn]

Hi Bill,

I mostly agree with your assessment, but I still think it's overly pessimistic towards hybrid boat systems.

I would temper your analysis with the following:

- first, a prop is a given, for the time being. We all agree that the prop design should be optimised. And probably will be.

- "diesel engine--electric generator--electric motor--gearbox--prop" - there's no reason for a gearbox; the electric motor can be selected for direct drive. Even reverse doesn't require gearing. The big saving here is weight and complexity.

- diesel engine efficiency - I'm not very knowledgable on combustion engine design, but I'm finding information that states that present-day diesel engine technology can approach 50% in thermal efficiency, in some cases. (source) So I'm optimistic that marine-application diesels may yet get into the 40% range. An important advantage of the hybrid situation is that it will be easier to optimize diesel performance as a generator than it will be for direct drive marine engines, with their restrictions around the gearbox, physical access, wider required operating range.

- currently, a larger cruising boat is going to either use their primary engine as a generator (which is not optimal) or they're going to have a separate genny. In a hybrid system, the combustion engine is optimised as a generator period , so there's no compromise needed.

- I don't quite understand your point about prop regeneration. I don't think anyone is suggesting that prop regeneration when under sail could supply most of the energy required for serious motoring. I think the best-case scenario is that a day's sailing might produce enough prop regeneration to keep up with the boat electronics while sailing, and several minutes of power for docking at day's end.

Regarding the case for hybrid systems, I think that energy from prop regeneration is sort of a happy side benefit from having electric propulsion, that can keep the typical cruiser's batteries topped off, to augment solar or wind generation, and reduce the needed run-time of the diesel generator.

- yeah we all agree that better battery technology will be a game changer, but it can only enhance the practicality of a hybrid system. I believe that currently-available battery technology is sufficient to make hybrid systems feasible.

- finally, a hybrid system is more "forward"-facing in that when a better alternative to internal combustion comes along, only the generator needs replacing, the electric motors and circuitry can remain.

Interesting discussion, folks, thanks. It's sort of a small example of the bigger issues around energy efficiency.

 

[Ross]

Rube Goldberg here. Run the diesel for propulsion, use the hot exhaust for heat to supply a Sterling cycle engine and use the waste heat from the sterling to fire a boiler to make steam to drive a turbine and the waste heat from the boiler to fuel an absorption cycle refrigerator. Run all of the accessory systems with the Sterling and the turbine.

 

[Bill Roosa]

now your talking

A guy in the 60s did just that kind of setup on a 4 cylinder gas engine and went from 90 to 400 HP just using the waste heat off the engine.
I think this is a much more likely solution to increasing the efficiency of a hybrid engine.

 

[Ross]

Re: now your talking

An IC engine is a wonderful way to burn fuel but it doesn't convert much of the heat to work. Kohler came out with a system a few years ago using a natural gas fueled engine to drive a generator for residential electricity and a compressor for AC. The waste heat was used for cooking, water heating and winter space heating.

 

[COOL]

The more I look in to it the more I am convinced that
an electric motor is the perfect propulsion for a sailboat.
Electric motors are quiet, they are always 'on', you just
put them in gear and go. They require minimal maintenance.
You can replace the entire motor in 15 minutes, and you can
carry it by hand.
IC engines are smokey and noisy, and you have to warm them up
for 15 minutes before you can use them for the 5 minutes it takes to
power out of the slip. IC engines have hundreds of moving parts
wearing out at various intervals.
IC engines get hot and take up huge amounts of space.
For my purposes an electric propulsion system will be
much lighter than my current diesel engine,
and will be more reliable.

 

[NotCook]

Plus a fan

Rube Goldberg here. Run the diesel for propulsion, use the hot exhaust for heat to supply a Sterling cycle engine and use the waste heat from the sterling to fire a boiler to make steam to drive a turbine and the waste heat from the boiler to fuel an absorption cycle refrigerator. Run all of the accessory systems with the Sterling and the turbine.

And a fan to push the sails...

(yeah, I know...)

 

[Ross]

The more I look in to it the more I am convinced that
an electric motor is the perfect propulsion for a sailboat.
Electric motors are quiet, they are always 'on', you just
put them in gear and go. They require minimal maintenance.
You can replace the entire motor in 15 minutes, and you can
carry it by hand.
.

I'll bet that you can't carry a continuous duty ten HP electric motor.

 

[COOL]

I have not found many specs listing motor weights.
Would a 10HP weigh approx 110lbs., or more?

 

[Ross]

3 phase ten hp approximately 180 pounds.