Continuously Variable Transmissions

[ancient kayaker]

... I'm convinced that D/E is not economical for anything that small ....

-I'd agree with that. Although switching efficiencies have reached the point when even a small DC installation can reach the efficiency break-even point, the higher initial cost is, currently at least, too high. Also, while DC systems have higher efficiency than AC, size for size, there is the potential safety impact of higher voltage from end-to-end. But if you need the control features the DC system has been the way to go for a few decades.

Dances with Turkeys ... BTW, is that an earned name or did you just make it up? I got one, "He who runs from distant coyote" from an Eskimo once. I earned it, unfortunately.

If you’re ugly enough you would dance with anything!

Seriously though, I worked in a cubicle Wonderland for a couple of decades; each serf-slot identical to it's neighbor. Naturally they soon become individualized with signs, posters etc, even the odd qualification. Qualifications were considered a bit snobbish, and pointless as there were more doctorates per hectare in that place than anywhere else outside of academia; but I digress.

At one time the twisted individual next door proudly displayed the sign "you can't fly like an eagle when you work with turkeys." it never occurred to me that he meant me, until today that is; I guess I’m a bit short on humility; I thought it was an uncalled-for criticism of my other colleagues. So, in an attempt to lessen the hurt for my buddies I put up my own sign “Dances with Turkeys” - this was shortly after the release of the Kevin Costner movie. Took me 19 years to figure the joke was on me; is that a record?

 

[kroberts]

Ken I do´nt know why, but you WILL misunderstand me. We are NOT talking about different things. And I NEVER talk about toys, that was just principles, not installations, and principles are the same, no matter 10 or 10000 kw.


Thats not my reference, thats a article about diesel electric propulsion, I have nothing to do with it.

There was never a doubt about! But there is absolutely no NO NO sensible way to use that on a yacht.

Maybe that's the problem. I'm talking about large boats in general. A yacht spends most of its time at a dock. I'm talking about something in continuous use, for commercial or industrial purposes. On a yacht, you would never put enough hours on it to pay off the additional expense.

If you look at it, the marketing is different based on what scale you are using. The smaller stuff is aimed at ex-hippies who are trying to save the environment. The industrial stuff is aimed at somebody trying to run a business.

That is already a bit offensive right? I refer to some articles, I did neither recommend to buy some of these products nor was I looking for them!
And btw. Victron power management is at present the most sophisticated you can find on the market!

Stop talking nonsense!



Please do not try to tell me anything about Diesel engines, please do not!!!

Motor != engine. Diesel engines, electric motors. I made no reference to engines there.

Well you do´nt like to read them, that your thing, but then please stop talking nonsense here, you would have understood what I was pointing towards. And after all we are discussing yacht installations in general, not battleships.
I must say I´m definitely disappointed how stubborn you try to fight a senseless battle, and I know you know how senseless it is.

I stopped reading those articles because I have seen dozens of similar articles, studied them, and they are all about green-ness and not about practicality or economy. In terms of how the controller works, it's not that difficult in generalized form, but the details are a bit heavy on the math.

Somehow I missed that this was a purely yacht-oriented discussion. The topic is "continuously variable transmissions" and I somehow took that to be a discussion of what could be practical in any type of boat, from a rowboat to an oil tanker to an aircraft carrier and anything in between. I'm sorry if I missed the cue.

 

[apex1]

Maybe that's the problem. I'm talking about large boats in general.

The next point we are completely on the same road! I am always talking about large boats. I never became familiar with anything below 22meter. But maybe the fact that the thread opener in general is looking for techniques for his own boat made me think we are talking smaller sizes only here!?

A yacht spends most of its time at a dock. On a yacht, you would never put enough hours on it to pay off the additional expense.

Well, not my boats, but even they would not make it sensible.

The industrial stuff is aimed at somebody trying to run a business.

For that reason I never looked at anything substandard.

I stopped reading those articles because I have seen dozens of similar articles, studied them, and they are all about green-ness and not about practicality or economy.

That was (and is) a mistake Ken! Those articles have nothing in common with the purple trousers, green community, but are ALL about practicality and economy!
And here a advocat of Diesel EL systems, Nigel Calder goes pretty deep into the facts. The uncomfortable facts (for a advocat).
And Victron just makes clear how idiotically the average generator set is designed, and how to solve that prob.
All pretty clear, free of advertisement, and fully professional. And the best, it is valid for all sizes of D/E setups.

First thing, the advances in motor technology has gone fairly far recently. You can get light weight, strong motors which weigh very little now.

No reference to engines?
What did you guess where I got my engine info from? you know I buy some 140 Diesel engines per annum!? More than half of them are above 1000hp, less than ten below 200.


I may have expressed myself not very clear, I owned D/E driven vessels (commercial not toys) and know about their possible advantages AND disadvantages. For my next boat I played with the D/E idea more than 2 years before I gave it up (and thats not a toy too at 28 meter), believe me I know why.

I still think we are are not at opposite positions, we just did not understand each other.

 

[kroberts]

I'll take another look at those articles then. I saw the same old "same old" and stopped, maybe too soon.

I am positive we argue mostly for lack of understanding what the other guy is saying.

My "light weight, strong motors" comment was with regard to electric motors, not diesel engines. I was not trying to teach you about diesel engines. We had a language problem, maybe. There is a genuine difference between engine and motor in the English language, but often people don't use the proper term.

 

[wardd]

engines convert fuel in the combustion process

motors the fuel leaves in the same form it entered

 

[kroberts]

Well, in the technical sense it's an engine if it converts thermal energy to mechanical energy. It's a motor if it converts electrical energy to mechanical energy.

There are exceptions though, in the old sense an "engine" is any machine at all. Also in rockets, an engine is liquid fuel and a motor is solid fuel.

This is WAY off topic though.

 

[Fanie]

What it comes down to is mass flow. You want to move the largest mass of water possible, backward without wasting any energy.

K, I disagree !

What you want with a prop is the most possible kick WITHOUT moving water. Fortunately for us water is not compressable (except for the air in it) so that helps, but it is liquid (fortunately ) and does move. The most efficient prop would be the one that gives the most foreward thrust and speed and movieng the least amount of water. Moving water means slippage.

Only jet drives want to move as much water as possible, but they are less efficient than an open prop.

 

[Fanie]

I want to rephrase what I started with.

I have a constant speed motor - cannot adjust the speed. Lots of torque.

What drive can I connect to it to adjust propulsion speed, as well as reverse with. If possible also steer with it, ie like with an outboard with out a rudder.

 

[kroberts]

K, I disagree !

What you want with a prop is the most possible kick WITHOUT moving water. Fortunately for us water is not compressable (except for the air in it) so that helps, but it is liquid (fortunately ) and does move. The most efficient prop would be the one that gives the most foreward thrust and speed and movieng the least amount of water. Moving water means slippage.

Only jet drives want to move as much water as possible, but they are less efficient than an open prop.

Fanie,

The prop is acting on a fluid. As such it is a reaction machine, as in, equal and opposite motion and all that.

No matter what you do, the prop WILL move water. You can either move a little bit of water really fast, or you can move a lot of water not very much. You want to move a lot of water not very much, is what we're both saying.

You have a boat, it has mass. In order to move, you need to apply force backward in the water, and that water will move. The more water you move, the less distance any cup full has to travel in order to get your boat moving.

I guess that moving a lot of water a little distance probably looks like not moving it at all.

 

[Fanie]

Aye Ken, I know what you mean.

Now how about my post #98.

 

[kroberts]

Fanie,

I've studied some propeller design on my own and built a few (air) props, and I've studied 3-phase power, 3-phase motors and a little bit of the controller logic. Some in school and some on my own. I have no practical experience in building 3-phase anything, except in RC models in which case they call it brushless DC. I've wound/built a couple brushless DC motors from kits, mostly to learn what was going on.

As my signature says, I'm not much of a boat expert. I try to not pipe in on things I'm totally ignorant about. As you have no doubt noticed by now, I'm not always very good at keeping my mouth shut. Since this topic is CVT, I thought I would chime in on one.

Both hydraulic (I also researched this a bit) and electric CVTs are expensive no matter what, and high-loss unless you have a really good controller that helps you manage things better.

An in-flight adjustable prop is common hardware on both aircraft and water applications above a certain size. There is a reason, it's both cheap and gets you reasonably close to the same efficiency you could get with a more expensive technique.

FWIW, my interest in boats includes only those which do not have propellers. I want a small sailboat. I've been reading some recommended books (some recommended by Richard) and when the time comes I will probably ask the boat experts for more advice before I choose.

 

[apex1]

I have a constant speed motor - cannot adjust the speed. Lots of torque.

What drive can I connect to it to adjust propulsion speed, as well as reverse with. If possible also steer with it, ie like with an outboard with out a rudder.

If it turns at 1500 rpm (or a multiple of it) a 50Hz genny and El motor. If it turns at 1800 rpm (or a multiple of it) a 60Hz genny etc. You could go DC, but have a deep look in a deep wallet first.

If that is not the case, a CPP.

 

[Fanie]

Aparently some auto's use a clutch that has a liquid that acts as a clutch, hence no clutch plates with mechanical wear. Being an auto box it has reverse and up to 6 foreward speeds to select.

 

[apex1]

7 Fanie, 7 is standard on German top class cars. But I would´nt like to have them in a boat! Too weak and too many ways to kill them.

 

[Yellowjacket]

Getting back to the original question in the thread, nobody has mentioned that the differential speed requirements and the power load curve for a boat is totally different than an auto, and consequently, most boats don't really need a set of gears or a cvt to do what they need to do.

First of all, the speed range for a boat is relataively small. That is, a large boat has a maximum speed of something on the order of 30 mph. At their maximum speed a boat needs all of the power it can generate, so the engine is running at maximum rpm at that conditon. An auto only needs about 10% power at lower speeds and, so as to reduce the noise and wear, it uses a transmission to slow down the engine. Moreover, a car has a much higher speed range (up to 100 mph or a lot more) so a gear ratio that could drive them that fast wouldn't have any torque for acceleration at low speeds. Also note that cvt's and six speed transmissions are a pretty new thing. My sister had a GTO that had a two speed powerglide transmission (with a torque converter) in it and it worked fine...

At really low speeds boat props have high slip. A prop that is sized to work effectively at high speeds is smaller than what would be optimum for very low speed work. They act basically like a torque converter, and provide higher thrust. In essence props act much like a transmission in that they have effectively a torque converter effect that allows them to slip and generate thrust. They are not highly efficient out of their primary operating range but there is a substantial thrust multipication effect and that works to get the boat moving and up into a range where they are efficient.

Aside from the fact that cvt's aren't all that efficient and can't (because they rely on hertzian contact to transmit force thru friction) transmit big torque loads, they really aren't necessary for a boat.

If you really want to turn a big prop (for low speed grunt) and jump out of the hole, a lot of drag boats have used two speed (and as many as four speed) transmissions, but part of that is the larger speed range (from zero to 100+) and the fact that they want big torque at lower speed to help them leap out of the hole.

While a variable prop can improve efficiency in some cases, unfortuately the larger hub and higher underwater drag tends to limit their use to larger slower applications.

As for DE drives, the problem is simply the weight of the generator, when coupled to a typical diesel is so huge that unless you are talking about a displacement application it makes no sense. The problem there being that the generator running at the low speed that a diesel runs, is very big. If you had a high speed alternator (like that on a gas turbine) it might make sense, but on a diesel it is just too heavy.