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Is little Nimby angry because his electric ideas don't stand up to the laws of physics?

Is that why he lashes out at catamaran people? lol

 

wow, you really are not professional are you? "little Nimby"?
always attack the messenger not the message.

 

If you have an extra small kicker outboard and a 5-6 gallon tank, you have a fully redundant "get-home" motor to get you home or back to the ramp. In case there is a problem with engine, fuel, or electrical. For 100 lbs of weight to carry along.

 

Mr. Harris. You said everything I would have liked to say... except better.

 

all true, except implication of a lack of understanding the law of physics
because one wants to use a hybrid system?
weight, efficiency, speed, cost, are all factors. Just because you might think weight and speed are important, someone else might not.
It has nothing to do with ignoring the laws of physics, it is all about priorities.
So the "bottom line" is NOT energy/wt of fuel, it is WHAT IS IMPORTANT TO YOU, if energy/wt is YOUR bottom line, that is fine, just don't assume or imply others must share those same concerns.

 

Whoa, fella! Maybe you need to read what I wrote before firing from the hip. The bottom line is that if you want to move a given mass any distance in,on or across any medium at a given speed then you need a certain amount of energy.

If you increase the mass, you increase the amount of energy needed to move it at the same speed. Using a power source that demands heavier energy storage means you need more energy; there's no way of getting away from this fundamental principle by assuming that technology can magically change the laws of physics.

If you don't believe me, then take a look at the relationship between displacement and the power requirement for any boat.

If you reduce speed to reduce the power requirement then the endurance needs to increase to get the same range, which means carrying more stored energy (so adding more mass), so that doesn't fix the fundamental problem either. Certainly hybrid systems for boats don't make much sense, as there simply isn't the margin to give an overall efficiency gain.

The fundamental issue is that massive difference between the energy density of electrical energy storage systems and the chemical energy density of fossil fuels. With fossil fuels being around 60 times lighter for a given amount of stored energy there's no way that electric systems can come close in terms of overall performance.

 

The laws of physics also says that a body in motion stays in motion, so
according to this law I can travel around the world carrying NO FUEL.
This is a fact and a law of physics, nothing you say can deny it.
A container ship is extremely heavy, do they just not get the laws of physics?

A sailboat can travel the world without any fuel,
did they just violate the law of physics?

An airplane can travel the around the world without any fuel, did they just violate the law of physics?
http://www.solarimpulse.com/

Gasoline has more energy than batteries for a given weight.
Thank you for that important fact.

Again, you miss my point, which is any design has GOALS, just because your goals might be different than mine doesn't mean mine violate laws of physics.

 

Sorry, but this is where your total ignorance of basic physics really shows. As you've chosen to be blunt, I will respond in a like manner.

You need to go and read up on some basics. Start with taking a look at the causes of resistance to motion. You'll quickly learn that bodies in motion are restrained by drag from their motion through fluids (be those fluids air or water) and that, in the case of a surface vessel, they also face additional drag as a consequence of moving through the air/water interface (specifically wave-making resistance).

There is a great deal of reference material available, and knowledge expressed elsewhere on this forum, that can help you grasp the various relationships between mass, velocity and resistance to motion. The basics are that if you increase the mass of a vessel you increase its displacement, which increases its wetted area, which increases its viscous drag.

 

uh huh. "total ignorance"???
You need to stop typing yourself so smart and listen to what others say.
You fail to understand completely the point. It has nothing to do with fluids
or laws of physics. You still don't get it.

 

Except for the drag of moving through water!
Boats don't move in a vacuum like a space craft.

Using the force of the wind.
With a hybrid, what "free energy" are you tapping? There isn't any to be had. With boats, you don't frequently apply brakes or gear down to slow down.
That leaves the advantages:
1.) ability to run the engine at it's optimal rpm -- trade off huge weight of batteries and cost
2.) being able to run silent in a harbor or short trip -- trade off high cost of equipment, but I can appreciate some people would be willing to pay this.
3.) very specialized applications

Can you explain your point? I understand silence being a design GOAL with associated costs and drawbacks.

 

Of course not, so this comment makes as much sense as mr. harris saying a hybrid defies the laws of physics. One law of physics means little by itself. An air tank can't hold enough air to breath for 30 days at sea, so obviously scuba divers were stupid fools that didn't understand physics and can't breath underwater. Now let me spout 20 facts about air density to back up my claim that scuba divers are ignorant of physics.

A wind generator. I have not yet heard of anyone that can take the power of the wind and produce diesel fuel from it. Maybe someone can figure it out, but producing electricity from wind is pretty well understand physics.

You have already made the point of (2) above.
That can be a sufficient goal for adopting a hybrid drive system.

As a said earlier, the topic has been pretty thoroughly discussed in the archives on this forum, no real reason to rehash them.

 

Here is the last word on how to build a hybrid

http://www.topgear.com/uk/videos/amphibious-1

 

You're intent on trying to support your view without grasping the fundamental principles that determine the power requirement for any vessel. It is, I am afraid, an indisputable fact that increasing a vessels displacement (by making it heavier with batteries, hybrid systems, cargo or whatever) will increase the power required to move it. This increase in power outweighs the tiny efficiency gain that can be obtained by using a hybrid propulsion system, because the peak to mean power usage ratio for boats is relatively low.

Even in cars, with their high peak to mean power usage ratio, the benefit is pretty small, maybe a 10% efficiency improvement, if that. A comparison of the fuel consumption of hybrid cars with conventional cars of the same size, weight and performance quickly shows this to be the case. In fact, some high efficiency diesel cars are actually more efficient than equivalent hybrids.

If you took the time to do some research on these principles and gained a better understanding of some of the fundamental principles you'd quickly see why hybrid technology doesn't offer any advantages for ordinary boats. It does for vessels that are, in effect, floating power stations, like cruise liners and warships, but only because their house power load can exceed their slow cruise propulsion power load.

Here's a worked example for a small inshore fishing boat that has a requirement for fast transit to and from the fishing grounds combined with a long period operating at low speed whilst fishing. It's probably close to being the highest peak to mean power usage requirement for a boat that I can think of, so perhaps the only one where a hybrid power plant might make sense.

Let's assume that the boat has a displacement hull and has to travel 10nm out and 10nm back to the fishing grounds.

Fast transit cruise speed is 8kts. Let's assume that the boat needs around 40hp to cruise at this speed.

Let's also assume that the boat needs to cruise at 2kts when fishing and that it needs to stay out fishing for 8 hours.

The relationship between power and speed for a displacement boat below the onset of significant wave making drag roughly approximates to a cube law, so the power required to do 2kts will be around 0.5hp (ignoring losses).

The time spent at 8kts is 2 1/2 hours, so the energy used during this transit phase will be 40hp x 2.5hrs = 100hp hrs, or 72.6kWhrs. This is about 96% of the total energy requirement.

The time spent at 2kts is 8 hours, so the energy used during this operational phase will be 0.5hp x 8hrs = 4hp hrs, or
2.984kWhrs. This is about 4% of the total energy requirement.

Total energy usage is 75.584kWh and the mean power used over the 10 1/2 hour total trip will be about 7.2kW. The petrol or diesel engine could be sized to deliver a constant 7.2kW, or around 9.7hp, rather than the 40hp that would otherwise have been needed.

Now let's size the electric motor and battery pack. The electric motor needs to deliver 40hp during the fast transit. The battery pack needs to deliver the fast transit power, less the power generated by the engine, for the duration of the transit period. Ignoring all the losses inherent in power generation etc, we can estimate that we need a bit more than 30hp from the batteries for the 2 1/2 hour transit time, so more than 75hp hrs, maybe about 56kWhrs. For longevity, even lithium batteries need to be sized so that they don't discharge below about 20% capacity, so the true battery pack size will have to be at least 70kWhr or around 252MJ. This gives a battery mass of around 350kg if you use the best lithium cells around at the moment. An electric motor that can deliver 40hp will weigh around 100kg, and the big generator on the engine will weigh around another 20 to 30kg. The cabling, charge controller, motor controller etc will add maybe another 10kg. All told the hybrid components will add around 480 to 500kg to the propulsion system weight,or around 1/2 ton.

The efficiency gain that will be achieved from using the smaller engine will be the difference between the engine's BSFC at 40hp and 0.5hp for the single engine system, and that for an engine of around 10hp running at peak BSFC. It's likely that the 40hp engine will be close to peak BSFC during the fast transit, and around 20% down on peak during the slow fishing phase.

In efficiency terms, there will be no gain in efficiency during the fast transit for the conventional engine arrangement, but for the 4% of the total energy used during the fishing phase there might be a 20% improvement in fuel efficiency from the smaller engine running at a higher % power and hence BSFC. A 20% improvement on the 4% of total energy used during this phase would give a total efficiency improvement of less than 1%, for an increase in vessel weight of at least 1/2 ton. Adding 1/2 ton of displacement will increase the energy requirement by more than 1% in all probability, so a hybrid makes little sense.

What might work for a boat with this sort of mission profile is a separate electric auxiliary propulsion system sized for the 8 hour fishing phase. This isn't a hybrid propulsion system in the way we normally talk of hybrids. The auxiliary propulsion system could be electric, as the energy requirement is modest (around 3kWhrs) and the total electric motor, control systems and battery pack weight could come down to around 30kg using a 1hp motor, 5kWhr lithium battery pack and associated controllers and wiring. It's likely that the power generation capability of an existing 40hp engine would have enough excess capacity to charge the battery pack up during the high speed transit phase, perhaps assisted by some form of solar or wind generation to top the battery up whilst out fishing, so this might make a viable system for this particular usage profile.

Jeremy

 

Interesting debate. I realize it's old. Perhaps opinions have changed in the last year? Anyway, simple principal of physics is being overlooked here. Waste. An ice of any variety uses more energy to produce thrust or torque. There is a minimum RPM that has to be maintained to keep the engine running. Go below that threshold and the engine stalls. Reverse is another issue for ICE's. To overcome this an ICE needs a transmission. Transmissions allow slippage in the drive train to achieve low speeds. Slippage equals waste. Electric motors don't need that slippage. They can spin on a trickle. Because there power curve is flat, they produce relatively the same torque at any speed, they have an advantage ICE's don't. No waste. They are superior at low speeds and use no power at idle.

Now for the cruising speed solution. An ICE has a prop that matches the RPMs the ICE needs to generate thrust at both cruising and low speeds. Many boaters "tune" their prop to gain speed or efficiency. All of this is a compromise due to the limitations and restrictions of the ICE always having to maintain minimum RPMs. For electrics the prop can be much larger since the torque available is equal at the low end and the high end of speed. A larger prop produces more thrust. Moves more water. And moves the vessel through the water faster.

Now how to power an electric. A battery pack to begin with. A couple of small generators to maintain the charge and limit the fuel burn when full power is not needed. Think Chevy Volt. The gas generator only comes on when the batteries are depleted. It powers the electric motor intil recharged or forever if need be. Its light and efficient so it has respectable torque for it's size. The boat has the efficiency of the prop and if the vessel is designed for this form of propulsion it will have an efficient hull. Think cats and trawlers. So the electric wins again.

Now for us boaters. We are a rich bunch aren't we? If you have the money to purchase a yacht. You probably have the money to burn some fuel. So why bother with all of this electric and hybrid nonsense anyway. You don't have a cruise line you operate. You don't run container ship across the ocean. Does any of this really matter to us? Maybe. Maybe putting less pollution in our water we love so much would be a good thing. Eventually change is coming. Whether we like it or not.

 

Couple basic points...

That's how a land vehicle's transmission works. Marine transmissions don't work like that. Since water is a fluid, you can idle the engine in gear without slippage. Do you own a boat?

This is true and it's one of the good points about electric propulsion.

That doesn't work. The generators you need in order to power your electric boat in the "forever mode" will be the same size (or actually a little larger) than the same ICEs you are trying to replace. In "forever mode", where do you think the energy to move the boat will come from? Generators with engines that are smaller than the regular ICEs you'd have in the traditional setup? Also, those generators are not "light and efficient." They are much heavier than the ICEs you are looking to replace. Why? They are the same size (or larger) than the ICEs, plus have a very heavy power head on then to make the electricity. Then, you have all that heavy cabling and all the controls. Diesel/electric definitely doesn't win when it comes to weight. I tried very hard to go diesel/electric because I have large house loads and it would have been fantastic. There was no combination of electric motors, controllers, batteries, cables and generators that weighed less than a pair of similarly rated Yanmar diesel engines. The electric gear only adds weight since the ICEs on the generators are going to be the same size (or bigger). It's unfortunate, but diesel/electric does not win on weight. It loses badly. Could work in cruise ships or even very heavy monohulls with lots of power consumption though. It certainly doesn't belong on a performance catamaran.

Yeah, it would be great. That's why I sail and am completing a boat that sails very *VERY* well... so I don't have to turn on my ICEs. In single figure wind speeds, I expect to get close to wind speed. That's because I don't have a heavy boat. With a diesel electric system weighing the boat down, I could never achieve that kind of performance. So, while those with diesel/electric systems in catamarans are polluting the environment because the winds are too light for their heavy boats to sail, I will be quietly and environmentally correctly sailing along.

I can't, for the life of me, understand why so many people forget that using the sails instead of motoring is actually the most environmentally sound method of propelling a boat. Why do you guys always talk about engines and the environment? They play no role if you don't use them often.