Continuously Variable Transmissions

[Fanie]

Why aren't these used for marine apps ? You can run the drive motor at a constant speed where it produces most torque while the boat speed changes.

Here's a nice video of how it works.

http://www.karting1.co.uk/continuously-variable-transmission-for-karts-test.htm

[Boston]

kinda makes me want to go rent a few beers and a cart
cool flicker Fanie
thanks

[alan white]

Infinite ratio drives have certain inherent inefficiencies which must be compensated for by allowing the engine to run, as said, at optimum speed. Then a 10% engine efficiency gain, for example, will be better than a 6% drive loss (and the loss due to extra transmisdsion cost)--- by 4%.
A typical boat will generally be capable of maintaining one optimum speed through the water, and it's assumed that the boat will run at that speed most of the time, so that the whole system (engine, trans, prop) can be optimized to that narrow speed range.
Of course, some boats might travel at variable speeds and it is possible that they could make better use of a variable speed transmission.
It's really a question of which usage would warrant the use of such a transmission. It would have to be a boat that spent a lot of the time at different speeds.
A good variable pitch propeller should be as or more efficient as any variable speed transmission. This is like being able to enlarge your car tires as you go faster. If a car could do that, it wouldn't need a transmission with gears.

[CDK]

Why aren't these used for marine apps ? You can run the drive motor at a constant speed where it produces most torque while the boat speed changes.

Here's a nice video of how it works.

http://www.karting1.co.uk/continuously-variable-transmission-for-karts-test.htm

The CVT, invented by Huub van Doorne 30 years ago and improved numerous times, never got wide acceptance because the metal belt is very difficult to produce, especially when a lot of horsepowers are involved.
A few small Japanese cars use this system, the patented belt being supplied by the Dutch company. They still seem to be experimenting with larger ones.

[alan white]

Even further back, didn't the Dutch company Daf build a car with a CTV? the Subaru Justy can be had with ther CTV as an automatic transmission, as well as most snowmobiles built today. All of these had rubber belts though, I think. I didn't know about as metal belt.

[Fanie]

It seems the advantage of such a setup is that you can run the motor for most speed, for most torque or for best economy, all three usable for marine app.

Lots of cars have them nowadays.

[CDK]

Even further back, didn't the Dutch company Daf build a car with a CTV? the Subaru Justy can be had with ther CTV as an automatic transmission, as well as most snowmobiles built today. All of these had rubber belts though, I think. I didn't know about as metal belt.

DAF stands for van Doorne's Automobiel Fabriek. The did manyfacture a passenger car with 2 giant V-belts as a transmission, but people got sick of having them changed every year and production facility was closed down several decades ago. They split up in a still successful truck factory and the CVT manufacturer who produces the metal "push-belt".

[FAST FRED]

"Of course, some boats might travel at variable speeds and it is possible that they could make better use of a variable speed transmission.
It's really a question of which usage would warrant the use of such a transmission. It would have to be a boat that spent a lot of the time at different speeds.
A good variable pitch propeller should be as or more efficient as any variable speed transmission."

I believe a 2 speed tranny would make most sense with a boat that has a Hi Cruise speed and a Low cruise speed.

While a CPP would allow the optomisation at EITHER speed , it could not do both.

A vessel that could shift to a higher shaft speed when running slowly would be able to keep the engine in a better more heavily loaded range , and would gain efficiency.

Weather that would be worth the cost of a 2 speed ZF and CPP , would depend on the annual hours of use.

FF

[Frosty]

It was Daf variomatic, the belts were not a prob as I remember. This idea is ubiquitous in small motorcycles I would say more than half the motorcycles made in Thailand are variamatic.

It works by weights on one hub expanding the two parts of the hub together so reducing the space for the belt making the V belt ride out. The driven hub would have similar 2 parts but have springs, the weights with centrifugal force over comes the springs. The belts were expensive so I used a B size V belt perfectly for a dollar.

The Daf would fail only due to vacuum pipes from the manifold that worked the drive hubs unlike the motorcycles. The vacuum pipes would often break and frighten the hell out of the owner . I bought quite few in Car auctions in my day.

I remember Ford making some auto transmission with a metal belt rather like a spandex wrist watch strap, it was unusual as the belt would push and not pull.

[Carioca]

The CVT, invented by Huub van Doorne 30 years ago and improved numerous times, never got wide acceptance because the metal belt is very difficult to produce, especially when a lot of horsepowers are involved.
A few small Japanese cars use this system, the patented belt being supplied by the Dutch company. They still seem to be experimenting with larger ones.

I was unaware that DAF is only 30 years old, although the chronology of the CVT invention sounds about right !

I had always been under the impression that DAF was a Dutch re-start from post-WW II, similar to BMW and NSU.

[Frosty]

Bit more than 30 years,--45 at very least.

Daf are well known for heavy goods vehicles in Europe and are popular, even against Volvo etc

[Carioca]

Bit more than 30 years,--45 at very least.

Daf are well known for heavy goods vehicles in Europe and are popular, even against Volvo etc

If my memory is not failing me, I believe I saw DAF at the Earl´s Court Motor Show (London, UK) in the late 60´s - think it was ´69 - when NSU presented its Wankel-engined passenger car.

Prior to this, had heard/seen DAF as a heavy goods vehicle manufacturer. No DAF lorries in London in those days, though !

[apex1]

While a CPP would allow the optomisation at EITHER speed , it could not do both.FF

Fred the opposite, a CPP does exactly that. It optimizes the systems efficiency at ALL displ. speeds. (as long as the vessel is´nt operating at a narrow speed range all time).

And the Daffodil entered the market in 1961, so the system is older than Cornelis remembers, 50 years.

[marshmat]

Nissan is offering CVTs as an option in several of its cars right now.

The trouble with adapting them to marine use is the same problem that is encountered when adapting car engines to marine use. Namely, sustained transmission of high torque. It took many years and many millions of dollars to come up with a CVT that could handle the Nissan Murano's 265 hp or so. But the car (thing?) only ever produces full power for ten seconds or so at a time, and spends 98% of its operating life loafing along at much lower RPM and torque.

In a boat, the transmission is expected to handle the full power and torque of the engine, continuously, for thousands of hours before needing work. Think how long your car's gearbox would last if you drove it like a NASCAR racer, day in, day out. Would you get 250,000 km on it before needing any work? But we routinely expect that kind of duty cycle and lifespan from our marine gears.

Plus, we boaters can get a lot of the same benefits with a CPP or, in the case of heavy planing hulls, a two-speed gearbox. Both of which are mechanically simpler, easier to make really beefy, and easier to fix when they break.

[CDK]

Bit more than 30 years,--45 at very least.

Daf are well known for heavy goods vehicles in Europe and are popular, even against Volvo etc

DAF even existed in the 2nd world war, but under another name.
I nowhere wrote that DAF was 30 years old, only that van Doorne invented the present CVT that long ago.
They are separate companies now, DAF being a big player on the heavy lorry market in Europe.

The old Variomatic was the predecessor with V-belts. The Dutch called it a girder belt transmission. Most drivers were female, elderly and had a driving license restricted to this vehicle only (!)

[Fanie]

Most drivers were female, elderly and had a driving license restricted
Blimey CDK, that explains it then.

[Frosty]

DAF even existed in the 2nd world war, but under another name.
I nowhere wrote that DAF was 30 years old, only that van Doorne invented the present CVT that long ago.
They are separate companies now, DAF being a big player on the heavy lorry market in Europe.

The old Variomatic was the predecessor with V-belts. The Dutch called it a girder belt transmission. Most drivers were female, elderly and had a driving license restricted to this vehicle only (!)

I was an elderly lady with a restricted license in those days.

Geeeez CDK they were not a bad little car, they went ok just had this unusual constant RPM thing which was too radical,-- as is most new things.

You are suggesting they were inferior in some way and more for incapacitated drivers, Ive never heard such a thing.

[alan white]

I lived in Holland in the sixties and there were Dafs everywhere. I imagine the people who drove them were simply saving money, since the car was cheap to buy. You could get automatic transmissions in most cars back then anyway, so I assume people who couldn't drive standards had a lot of choices.
the same type of CVT is also used on all Univex bakery mixers, and they are extremely reliable. Their much more expensive competition, Hobart, uses a three or four speed transmission with gears. I've rebuilt many of those transmissions. The Univexes however only need a cheap belt replaced once in a while. In many years I never replaced the pulley mechanism, just the belts.
interestingly, subaru Justys with that type of tranny actually get better mileage than the gear tranny, due to higher engine efficiency. Yet, at least in the USA, it's the only car with a CVT.

[TeddyDiver]

All snow scooters use it, some ATV's too

[Frosty]

The Daf had 2 belts, one on each shaft to accomodate for the differential I assume.

No diff = cheaper

[Fanie]

Assume I have a motor that runs at a constant speed and have constant torque. That's it, cannot rev up or down. It either runs or stops.

What box should I put on it, I must be able to cruise with it as well as maneuvre in a harbour.

[TeddyDiver]

How about VPP :)

[apex1]

The DAF engine did not run on constant speed all the time, it revved up to about max torque rpm then ran constant through the widest range of speed the transmission covered, and when the max rate was achieved it revved up til max.

[CDK]

I was an elderly lady with a restricted license in those days.

Geeeez CDK they were not a bad little car, they went ok just had this unusual constant RPM thing which was too radical,-- as is most new things.

You are suggesting they were inferior in some way and more for incapacitated drivers, Ive never heard such a thing.

Sorry Frosty, I was not aware of your former life.
The cars were not inferior, but different. It was the limited driving license that was regarded as inferior. And of course the limitations of the rubber belts stood in the way of developing and marketing larger vehicles. Van Doorne tried to change that with the push belt CVT but the reluctance of car manufacturers to deviate from familiar technology remained, just as they would not accept Felix Wankel's rotary engine.

One special feature of the DAF's was, that the top speed in reverse was the same as in forward. This led to hilarious reverse racing events with caravans.

[Frosty]

Reverse ???? I forget,-- how did they select reverse?

[Fanie]

Assume I have a motor that runs at a constant speed and have constant torque. That's it, cannot rev up or down. It either runs or stops.

What transmission should I put on it, I must be able to cruise with it as well as maneuvre in a harbour.

[TeddyDiver]

Assume I have a motor that runs at a constant speed and have constant torque. That's it, cannot rev up or down. It either runs or stops.

What transmission should I put on it, I must be able to cruise with it as well as maneuvre in a harbour.

Like I said VPP (or CPP as some prefer to call it ;) ) A gearbox and propeller combination with you can turn from FF to neutral and reverse everything (engine, shaft, propeller) running at constant speed to same direction..

[Fanie]

Hi Teddy,

It looks like just the thing ! I wonder what they would set one back ?

I had a look at these http://www.redbackmarine.com/

Maybe Masalai or one of the .au guys can get a pice ?

[bonatèr]

Reverse ???? I forget,-- how did they select reverse?

Look, listen and love it: the DAF
http://static.rnw.nl/migratie/www.radionetherlands.nl/thenetherlands/weeklyfeature/050525dh-redirected

[Fanie]

Ha ! The French post what the Dutch should have :D

The DAF became known as an old ladies' car, because it was so easy to drive that it was a favourite among the elderly. Not having to concentrate on shifting gears meant that people could also pay more attention to traffic situations.
Sounds perfect for a boat. If the old lady drives it I could fish :D

[Carioca]

DAF even existed in the 2nd world war, but under another name.
I nowhere wrote that DAF was 30 years old, only that van Doorne invented the present CVT that long ago.......

I inferred (erroneously) ! My apologies !

[Carioca]

....... Van Doorne tried to change that with the push belt CVT but the reluctance of car manufacturers to deviate from familiar technology remained, just as they would not accept Felix Wankel's rotary engine.

You don´t have to deviate much from the status quo to get stumped, one way or the other.

Mechanics at GM dealerships all across the US massacred the 'variable-number-of-cylinders' concept no sooner than a Cadillac V-8 - equipped with the latter feature - got launched in the early 80´s.

Miracles happen sometimes, though. Like, for instance, Microsoft and Intel, heralding the demise of heavy-weight mainframe (computer) manufacturers, an exception or two, notwithstanding.

[Fanie]

Miracles happen sometimes, though. Like, for instance, Microsoft and Intel, heralding the
Yeah right. I upgraded my browser and then it took me two days to get the screen readable :(

[apex1]

Like I said VPP (or CPP as some prefer to call it ;) ) A NO gearbox and propeller combination with you can turn from FF to neutral and reverse everything (engine, shaft, propeller) running at constant speed to same direction..

Understand Teddy...;) well it is the term used by the industry manufacturing and installing CPP´s. For a reason: there are Variable Pitch Props available which allow to change the pitch manually when the ship is on the dry. So, CPP is right.


And before we start the next senseless debate here about the astronomic prices which some people believe to know, have a look here:

http://www.kastenmarine.com/CPprops.htm

Regards
Richard

[FAST FRED]

"Fred the opposite, a CPP does exactly that. It optimizes the systems efficiency at ALL displ. speeds."

Mu sugestion for a 2 speed tranny with a CPP was for a boat with a wide difference between High Cruse and Low Cruse.

Say 20k - 30k cruise on the high end and 7K at displ speeds.

The severe underloading at slow cruise would shorten a diesels engine life enough to pay for the complexity , better fuel efficiency would be a bonus.

FF

[apex1]

The severe underloading at slow cruise would shorten a diesels engine life enough to pay for the complexity , better fuel efficiency would be a bonus.
FF

Fred you cannot underload a engine with a CPP installation! That is the main advantage of the system, you easily double or triple the engines lifespan, and of course save tonnes of fuel.
Although a speed range that different is way out of sense (due to the hull form), even then I would assume (of course I never made such calculation) a CPP would be the better choice. And if it was for one reason only, it is a proven, reliable and comparable cheap system, a marine shift gear is not.

Richard

[Fanie]

How well would an automatic box work ?

[marshmat]

I think the losses in a car's automatic transmission would be rather large compared to any efficiency gain you might get by using one in a boat. A conventional automatic in a car typically increases fuel consumption by about ten percent over its stick-shift counterpart; lockup converters improve this a bit, but it's only in the last decade or so that they've figured out how to get the losses down to reasonable levels (and there's a lot of finicky, high-precision technology involved in doing so). Not to mention they're awfully expensive, a thrust bearing with CV shaft would be mandatory, and the darn thing would probably hunt in an out of lockup like a '90s Chrysler van every time you come off a wave. And you still have that pesky problem of Richard the German reminding you that a good CPP will be more efficient, more reliable and cheaper.

[apex1]

How well would an automatic box work ?

Good question, next question, please.







Never thought about.:?:


And you still have that pesky problem of Richard the German reminding you that a good CPP will be more efficient, more reliable and cheaper.
you could rely on that..........:p

[FAST FRED]

Fred you cannot underload a engine with a CPP installation! That is the main advantage of the system, you easily double or triple the engines lifespan, and of course save tonnes of fuel.

Changing pitch ONLY works until the prop cavitates, then the loading goes to Hell.

A 400hp engine propped with a CPP will not be loaded to its best efficiency at displacement speeds as the diameter cant be changed.

FF

[apex1]

[QUOTE]Changing pitch ONLY works until the prop cavitates, then the loading goes to Hell.
Thats theory yes, in fact you always change rpm setting AND pitch, and a large diam. prop at low rpm (the common setup with CPP´s) does´nt cavitate.

A 400hp engine propped with a CPP will not be loaded to its best efficiency at displacement speeds as the diameter cant be changed.

Thats haircutting. Does it matter if you have a specific consumption of 190 or 196 g/kw/hr ??? If the alternative consumption with a conventional setup is 300 g/kW/hr you can say you have a "perfect" installation, or not?

I see, you are not familiar with the "real life" operation of a CPP, you should study that. No offense in mind!

Richard

[FAST FRED]

I see, you are not familiar with the "real life" operation of a CPP, you should study that.

I operated a Swedish Double ender with 6 cylinder Volvo MD6 for a summer of charter.

With only one engine and a very heavy slow deep hull the main use for the CPP was to optomize motor sailing ,

a much smaller range than rated 1/4 power as you hope to attempt with some efficiency.

FF

[Fanie]

While it is great that such CPP systems exist, maybe the question should be if these are affordable. Seems like big ships use them, but none for the smaller market.

I e-mailed www.redbackmarine.com for a price indication, but got no answer back, maybe they have some problems.

[apex1]

a much smaller range than rated 1/4 power as you hope to attempt with some efficiency.
FF

Fred there is nothing I hope or believe or guess. I KNOW because I operated CPP systems over long periods. And there is not just a small range of efficiency, you operate your engine efficiently at ALL rpm settings. Though not equally efficient at all rpm, of course, much better than ever possible with any other propulsion system (DE included).

And it is the only perfectly proven, reliable and cheap system available from about 80hp upwards.As mentioned a dozen times here, the whole Scandinavian fishing fleet uses CPP systems since ages, they have no money to waste.
That answers Fanie´s question too:

While it is great that such CPP systems exist, maybe the question should be if these are affordable. Seems like big ships use them, but none for the smaller market.
I e-mailed .redbackmarine. for a price indication, but got no answer back, maybe they have some problems.

Forget about these toys Fanie. I am talking about the real stuff. Lookup Helseth or Hundested.
And of course it is almost impossible for a amateur builder to get a quotation from those OEM suppliers, they do´nt want to loose the industry as clients! The day Hundested gives you a price, is the day they have lost me as a customer.

Regards
Richard

[kroberts]

Back to the original purpose of the thread, that transmission on the go-cart is basically a snowmobile transmission. It uses a rubber belt.

In the 100 hp range, a snowmobile transmission loses around 30% of its power. I don't know much about the boating end of it, but snowmobiles I know. I understand the metal belt ones get on the order of 90% efficient, but I have no direct experience.

There are all sorts of extremely practical CVT's in boats: It's called diesel-electric. Basically a locomotive transmission. They are extremely practical for larger boats for exactly the same reasons they are practical for locomotives:

The electric motor generates only as much power as the prop requires at the moment.
The motor draws only as much power from the generator as it needs at the moment.
The engine RPM is maintained at a throttle level which barely supplies the required power.
The efficiency losses in the motor and generator are more than made up for by the lower fuel cost for turning the engine slower.
A 3-phase electric motor is far more reliable than any mechanical transmission.


Regarding variable pitch props, again I am not familiar with boats as much as with air props. The math still works out the same: A variable pitch prop only has ideal pitch along its entire blade in one position. You can rotate the blade to change effective pitch, but the blade will have higher pitch in one spot than the other at every position except for the one which it was cut for.

[apex1]

Regarding variable pitch props, again I am not familiar with boats as much as with air props. The math still works out the same: A variable pitch prop only has ideal pitch along its entire blade in one position. You can rotate the blade to change effective pitch, but the blade will have higher pitch in one spot than the other at every position except for the one which it was cut for.

Well, and the math tells you that a fixed prop has only one speed where it works efficiently, where the variable pitch prop has a wide range of efficiency.
But we should not use the term Variable Pitch Prop, because we are talking controllable pitch props here only. (the variable can be fixed at different angles when docked only)

[Fanie]

Forget about these toys Fanie. I am talking about the real stuff. Lookup Helseth or Hundested.
And of course it is almost impossible for a amateur builder to get a quotation from those OEM suppliers, they do´nt want to loose the industry as clients! The day Hundested gives you a price, is the day they have lost me as a customer.
I got to look them up if they won't give me a quote ? Right ! I would think that really stupid, simple, you never know what may come from treating someone well. Be a real bitch if I have to have my own made because they won't supply eh. Could become their worst competing nightmare :D

[apex1]

I got to look them up if they won't give me a quote ? Right ! I would think that really stupid, simple, you never know what may come from treating someone well. Be a real bitch if I have to have my own made because they won't supply eh. Could become their worst competing nightmare :D

I do´nt mind mate! Well, say as long as you will supply me too.:D

[kroberts]

Well, and the math tells you that a fixed prop has only one speed where it works efficiently, where the variable pitch prop has a wide range of efficiency.
But we should not use the term Variable Pitch Prop, because we are talking controllable pitch props here only. (the variable can be fixed at different angles when docked only)

I'm talking about both types. The variable/controllable pitch prop will cause a wide range of loads on your engine, which improves engine efficiency, but they don't make good use of all the power except in one case.

That case is usually full throttle or intended cruise, one or the other. So it doesn't matter much in most cases. But if the plop blades are set to near-zero thrust, the tips will actually be thrusting backward while the center thrusts forward. Once you start twisting those blades, it no longer is a true-pitch prop.

[TeddyDiver]

But if the plop blades are set to near-zero thrust, the tips will actually be thrusting backward while the center thrusts forward. If that's not neutral then it's r e a l l y s l o w and you don't have that option with fixed props :)

[apex1]

I'm talking about both types. The variable/controllable pitch prop will cause a wide range of loads on your engine, which improves engine efficiency, but they don't make good use of all the power except in one case.

That case is usually full throttle or intended cruise, one or the other. So it doesn't matter much in most cases. But if the plop blades are set to near-zero thrust, the tips will actually be thrusting backward while the center thrusts forward. Once you start twisting those blades, it no longer is a true-pitch prop.

Nonono, we cannot talk about both types! These are two completely different worlds.
The VPP has a very narrow range of adjustment and the ship has to be drydocked to adjust it (it is simply cheaper than buying a new cast prop), and is used in the commercial world only.
The CPP makes the perfect use of the given power in almost every case (well, except the unusual example you gave), whereas the fixed prop can be optimized for one speed or thrust setting only, and over- or underloads the engine in every other rpm setting.
So, it is exactly the opposite of what you stated.

What do you mean with "true- pitch- prop"?

Regards
Richard

[Fanie]

Controllable pitch propellers (CPP) for marine propulsion systems have been designed to give the highest propulsive efficiency for any speed and load condition. When the vessel is fully loaded with cargo the propulsion required at a given ship speed is much higher than when the vessel is empty. By adjusting the blade pitch, the optimum efficiency can be obtained and fuel can be saved. Also, the controllable pitch propeller has a "vane"-stance, which is useful with combined sailing / motor vessels as this stance gives the least water resistance when not using the propeller (eg when the sails are used instead).

http://en.wikipedia.org/wiki/Controllable_pitch_propeller

I did a search for VPP propellers and it referred me back to CPP propellers

[apex1]

Thank you Fanie, that will help me a lot in future. I must not come up with the same argument every week again.

Regards
Richard

[kroberts]

Richard,

A true-pitch prop is a prop in which the pitch (distance traveled forward) is the same from the tip to a point near the hub. Imagine turning the prop through a big container of jello, 1 revolution. If the angle at the tip would move the prop forward 60 inches, and the angle at the 3/4r station moves it forward 60 inches, and the 1/2r station moves it forward 60 inches, then that means you have a true-pitch prop. The blades on a true-pitch prop are twisted so the tips have a shallower angle than near the root. It's very obvious on boat props.

For what I'm talking about, CPP and VPP is exactly the same. Each of these cases, the blade has been designed for some specific pitch, assuming it wasn't just whittled out of a stick by eyeball.

Even a perfectly flat blade is true-pitch at some angle. That angle would be zero degrees, no thrust. Any prop I have ever seen which was built for a real boat has a true-pitch form.

If you take a true-pitch blade on a cpp or vpp and reduce the angle of the blades, then the outer tip might be at 20 inches, the 75% station is at 40 inches and the 50% station is at 50 inches. The blade is working against itself. The tips are basically dragging in the water while the center part does the work. You are using power from the engine, but you are not getting very good return from your prop in terms of thrust. You are wasting energy.

The question is, would a CVT waste more or less energy than the prop?

I think that an electric drive (train transmission) would be more efficient and at least as effective.

IMO, a VPP by your definition is a total waste of time and money. A CPP might be a good option based on your needs, but a diesel-electric is (I think -- read my signature!) much better for a larger boat.

[Fanie]

Even a perfectly flat blade is true-pitch at some angle.
That must be at standstill only. The inner circle of the prop blades should have a larger pitch than the outer circle of the prop because the inner's speed is lower than the outer, hence needs to cut further to achieve the same distance.

I imagine the CPP blade gets designed to be best efficient at a certain pitch, same as a fixed prop, but even though less efficient when out of the optimal trim position, the CPP does offer the advantage of larger or smaller trim. The main advantage is not a larger overall efficiency on the prop, but rather the ability to adjust the prop for a certain speed to either adapt to different loads or a different speeds, still at the engine's optimal torque rpm which means the motor is always running comfortably which should enhance life span and at good fuel efficiency.

If a fixed prop is used the rpm has to be adjused for load or speed, meaning the motor go out of it's power band which results in poorer fuel economy and a shorter motor life.

I can imagine in difficult waters where you would normally 'ride the throttle' wave up and wave down one would have a considerable saving in fuel consumption with a CPP where the prop blade angle is adjusted. A fixed prop scenario would require extra fuel each time the motor is gunned up a wave simply because it operates out of it's power band.

I heard from someone a VPP has the ability to shorten stopping distances considerably by trimming to reverse, similar to brakes in a car.

[apex1]

The question is, would a CVT waste more or less energy than the prop?

I´m not sure, but guess more than a fixed prop at fixed speed (which does´nt happen). But sure that it cannot be as cheap and efficient than a CPP installation.

I think that an electric drive (train transmission) would be more efficient and at least as effective.

For sure not, the losses in a Diesel El setup are higher than in a conventional drivetrain. And of course far higher compared with a (almost no losses) CPP setup.

IMO, a VPP by your definition is a total waste of time and money.
Nono, the VPP has his place on new designs for example where a finetuning can mean several tons of fuel saved per day.

A CPP might be a good option based on your needs, but a diesel-electric is (I think -- read my signature!) much better for a larger boat.
No, sorry, a D/E is sensible (apart from exotic applications, like Icebreakers) in one case only! When you have a constantly high hotel load, and a variable propulsion load. Then you are better away with a different size of generators and a D/E setup. Cruise ships with Azipods for example.

and:
Just handed over a 8 hp SABB one-cylinder diesel to a customer after routine service. It has a cpp that matches the old stomper beautifully, making precision manoeuvering a delight! Which urges me to verify what Richard is saying about the performance of the CPP (not VPP....) in Scandinavian fishing vessels. The operation of these boats covers all speeds from high speed-low load steaming (first catch to sell gives best money!) to low speed-high thrust trawling. Some 20 years ago we saw fuel meters being installed, and they immediately made skippers change their engine loading routine.

Fuel savings resulting from procedure change were up to ~25 %, so the instruments were payed off within days for those who had run their engines with high revs/low pitch.

For Hullaby's application, I would contact the Servogear AS in Norway, they have cpp's well suited for this purpose. The reason why the cpp has lost market shares to conventional reverse gears, is probably the increased speeds of modern diesel engines; there has to be a reduction gearing anyway! Most "marine engines" are just road vehicle engines modified for "wet jobs". And, btw, a propos the thread on variable transmisssions; the cpp is a "continuously variable transmission", hydrodynamic style!


[QUOTE]The main advantage is not a larger overall efficiency on the prop, but rather the ability to adjust the prop for a certain speed to either adapt to different loads or a different speeds, still at the engine's optimal torque rpm which means the motor is always running comfortably which should enhance life span and at good fuel efficiency.

Right


I can imagine in difficult waters where you would normally 'ride the throttle' wave up and wave down one would have a considerable saving in fuel consumption with a CPP where the prop blade angle is adjusted. A fixed prop scenario would require extra fuel each time the motor is gunned up a wave simply because it operates out of it's power band.

I do´nt see a real advantage in that special case Fanie, but the general advantage of a CPP versus EVERY other propulsion is so big that it does´nt matter if I see this one or not.

I heard from someone a VPP has the ability to shorten stopping distances considerably by trimming to reverse, similar to brakes in a car.

Please mates forget the word VPP there is no such prop on the market for yachts!!! We are talking CPP only here.

And of course every CPP is much much faster responding than any gearbox / shaft system, it must not change the rpm just turn into reverse, thats done in 2 - 5 seconds. Compared with a conventional system it feels like throwing a anchor.

Richard

[Fanie]

Please mates forget the word VPP there is no such prop

You're right, sorry, my mistake. That's what I meant. Slip of the tongue.
CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP... :D

[apex1]

You're right, sorry, my mistake. That's what I meant. Slip of the tongue.
CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP, CPP... :D

Do you mean Controllable Pitch Propeller Fanie? Thats a nice idea!;)

[kroberts]

[QUOTE=kroberts;292471]
I´m not sure, but guess more than a fixed prop at fixed speed (which does´nt happen). But sure that it cannot be as cheap and efficient than a CPP installation.


A fixed pitch prop loses some efficiency at lower speeds, but the cpp/vpp loses a LOT of efficiency when you approach zero speed. You still turn it at some significant rate, possibly full speed, so your fuel goes toward heating the water.


For sure not, the losses in a Diesel El setup are higher than in a conventional drivetrain. And of course far higher compared with a (almost no losses) CPP setup.


That must be why EVERY modern locomotive uses them? The truth is that in spite of the losses, the benefits more than make up for the losses inherent in any other drive train they could come up with. Most transmissions require the engine to turn at a certain speed to make the wheels turn at a certain speed. If you are not at the point where available torque=load then your entire torque surplus is wasted fuel. with a mechanical transmission that means absolutely every speed except flat out.

The same math works for ships. A boat going slowly or riding waves can run the engine at a moderate speed, and the electric transmission makes best use of that power. When the prop comes out of the water the engine doesn't have to race, it spins up some but the motor controller can limit it.


Nono, the VPP has his place on new designs for example where a finetuning can mean several tons of fuel saved per day.


For designing a new ship? I can see that, but not as a viable prop for extended use.


No, sorry, a D/E is sensible (apart from exotic applications, like Icebreakers) in one case only! When you have a constantly high hotel load, and a variable propulsion load. Then you are better away with a different size of generators and a D/E setup. Cruise ships with Azipods for example.

and:




Please mates forget the word VPP there is no such prop on the market for yachts!!! We are talking CPP only here.

And of course every CPP is much much faster responding than any gearbox / shaft system, it must not change the rpm just turn into reverse, thats done in 2 - 5 seconds. Compared with a conventional system it feels like throwing a anchor.

Richard

[apex1]

[QUOTE=apex1;292481]

[QUOTE]A fixed pitch prop loses some efficiency at lower speeds

Wrong! A fixed prop loses at EVERY but the designed rpm!

You still turn it at some significant rate, possibly full speed, so your fuel goes toward heating the water.

Sorry what a complete nonsense is that? Please learn what a CPP is and does, before you step into such discussion. You are worlds besides topic.


That must be why EVERY modern locomotive uses them?

Are Loco´s driving through water? Every modern airplane uses jets, are jets a good ships propulsion? What are you playing here?
And btw. the reason for diesel el on railway systems is much simpler, only the el motor has enough torque to accelerate a laden train from zero.

The same math works for ships.

Sorry, nonsense! And you obviously have forgotten you own math.s on Diesel El. !?! That was in May:

Jimbo,
My comments on efficiency were with regards to a first-pass examination. Most electric motors or generators are in the 80%-90% efficient range. Then figure another 80% for the electronics, you get 0.8*0.8*0.8=51.2% efficient in just the transmission itself for a worst-case scenario. A gear box by itself is more efficient than the electronics.
However, you are right. The total system efficiency is higher because the engine doesn't have to turn so fast most of the time, and thus doesn't have to burn fuel that isn't being used.
It's the difference between the engine CAN DELIVER so much torque at this rpm, or the prop IS USING so much torque at this rpm.
here you pointed towards the perfect solution without knowing it....................... a CPP



For designing a new ship? I can see that, but not as a viable prop for extended use.

When will you stop talking VPP here? You do´nt understand them, so stop speculating about a topic which does´nt belong here.

Please do yourself (and us) a favour, study the systems of ship propulsion before you contradict next time.
http://www.wartsila.com/Wartsila/global/docs/en/ship_power/media_publications/brochures/product/propulsors/cpp.pdf
http://www.helseth.no/eng/default.htm
http://www.hundestedpropeller.dk/?id=4172
It is all said and written here several dozen times, there is really no need to start such a senseless dispute.


And back to topic: here was a nice comment on another thread:
To all on this thread: For years, may folks used vdrives with various automotive automatic transmissions, most also used custom version that removed the converter, but still utilized the shift points. I grew up near St Louis and spent many days in old V-drive flatbottoms running turbo400s, and powerglides. All of them had manual valve bodies. The goal was to have a big pitch prop for high end, and the low gear for getting onto plane and idle quality(carbs and blowers!). See http://www.rexmar.com/page133.html for a current version of the t400 for vdrives.
I think there are still some advantages to this approach, but the weight issue needs to be overcome.
Jeff D Rauscher

Regards
Richard

[kroberts]

[QUOTE=kroberts;292688][QUOTE=apex1;292481]

,

Wrong! A fixed prop loses at EVERY but the designed rpm!


EVERY propeller ever made suffers from that. Fixed, adjustable, controllable, variable, ducted, unducted -- insert your type here. A prop is a prop is a prop with regards to operation at non-design speeds. If the makers of cpp's could make their blades so that they are more efficient at a wider range of RPMs then the same approach could be used on fixed props to the same end.

The CPP prop's only advantage is that it can change pitch to reduce speed without changing engine speed, thereby improving coupling between the engine and the water. It replaces a multiple-gear (or otherwise adjustable ratio) mechanical transmission between the engine and the prop.

For every pitch you could achieve with a CPP, a FPP could be made which would outperform the CPP at every RPM while both props had the same pitch, for the same engine and on the same ship. EXCEPT ONE! The design speed of the CPP, it is possible that the CPP could match efficiency.

None of the CPP's change the amount of blade twist, so at EVERY pitch position except their design position they suffer from a loss of efficiency because of an inconsistent pitch along the blade length. This is in addition to any inefficiency because of non-standard RPM.



Are Loco´s driving through water? Every modern airplane uses jets, are jets a good ships propulsion? What are you playing here?


http://en.wikipedia.org/wiki/Gas_turbine


And btw. the reason for diesel el on railway systems is much simpler, only the el motor has enough torque to accelerate a laden train from zero.


So none of the steam trains written about in history books actually worked? Of course there are other mechanisms which could make the locomotive work. An electric transmission is simply the best one.

My reference to locomotives was simply to describe the type of transmission in a fashion everyone has reference to.

Check this out.

http://www.ossapowerlite.com/tech_library/fuel_efficiency/fuel_efficiency.htm

It makes every point I was trying to make for diesel electric, only since it's written by a professional you will not automatically disbelieve the way you do with me.

For the record, I am not arguing against a CPP, it is obviously a very good solution for many marine applications. I'm just pointing out that like any other system, it has weak points. It is not a perfect solution. Neither is diesel-electric. Each has advantages in some situations which the other does not.

[apex1]

[QUOTE=apex1;292695][QUOTE=kroberts;292688]

[QUOTE]EVERY propeller ever made suffers from that. Fixed, adjustable, controllable, variable, ducted, unducted -- insert your type here. A prop is a prop is a prop with regards to operation at non-design speeds. If the makers of cpp's could make their blades so that they are more efficient at a wider range of RPMs then the same approach could be used on fixed props to the same end.

Correct

The CPP prop's only advantage is that it can change pitch to reduce speed without changing engine speed,

Wrong, think about that again. Thats not the way you use a CPP.

For every pitch you could achieve with a CPP, a FPP could be made which would outperform the CPP at every RPM while both props had the same pitch, for the same engine and on the same ship.

No, they are equal, none outperforms the other.

None of the CPP's change the amount of blade twist, so at EVERY pitch position except their design position they suffer from a loss of efficiency because of an inconsistent pitch along the blade length. This is in addition to any inefficiency because of non-standard RPM.

Right, but minor.

http://en.wikipedia.org/wiki/Gas_turbine

Whats that? We know CODAG / CODOG installations, we have had gas turbines even in large express ferries (Finnjet), and we know they are fuel consuming like hell.


So none of the steam trains written about in history books actually worked? Of course there are other mechanisms which could make the locomotive work. An electric transmission is simply the best one.

Steam propulsion is a extreme high torque propulsion, thats why it worked very well. El propulsion is high torque too, thats why you do´nt find diesel engines in trains in the civilized part of the world. Of course where a proper el. supply is´nt at hand you have to go diesel electric to achieve waht you need, but that does´nt mean it is the perfect solution.


http://www.ossapowerlite.com/tech_library/fuel_efficiency/fuel_efficiency.htm[/url]

Thats well known too, and has proven to be NOT as efficient as they claim. I recommend to read a neutral and professional article about diesel / el. "Nigel Calder" at Professional Boatbuilder last year! There you find the plain truth for a yacht installation.

only since it's written by a professional you will not automatically disbelieve the way you do with me.

Well, as a pro I tend to be as sceptical with other pro´s statements as with a well educated amateurs one. Especially when they try to sell me their product. And I did not disbelieve you, I just know better from experience, thats it.

For the record, I am not arguing against a CPP, it is obviously a very good solution for many marine applications. I'm just pointing out that like any other system, it has weak points. It is not a perfect solution.

I fully concur, it is just only the best solution at present for all yachts, the fishing fleet, and most of the commercial fleet too. There is ONE single advantage of a D/E system where a CPP cannot compete, as mentioned a thousand times now. When your Hotel load is constantly high (in relation to propulsion), then a full D/E system outperforms every other system.
(I do´nt talk special purpose vessels like Icebreakers, where highest torque at lowest speeds are the main requirement).

And when we talk about efficiency we should not forget that anything but a conventional or CPP drivetrain is additional cost upfront and hardly pays in common boaters life.

Richard

[kroberts]

Richard,

Somehow we are crossing wires. The very documentation you pointed me at about CPP seems to support my position. As well, you criticize me for giving a reference to a commercial company with skewed information, and your first link is a commercial reference to a company which is making self-contradictory claims.

At this point I don't think I care enough to continue the discussion.

[apex1]

????????????
Have´nt seen Wärtsilä making any of such self contradictive statements.


But ok, your estimation.


As much as I enjoyed your valuable input on other threads (especially about hovercraft), as much I do´nt enjoy your senseless contradiction here. You just do not know how a CPP system works. Thats ok, 99% of the other Forum members share that. But you try to teach me on a topic I am familiar with since nearly 40 years. For what?

[kroberts]

Ok, first problem and basically the entire reason for me to hang onto this subject so long.

Optimal means best possible, right? By definition of the word. An optimal thing cannot be improved on by any known means.

Page 3 of that document, first paragraph: the propeller is designed for optimal
performance in all operating conditions.

This is not possible. Once you cast that propeller, it has blades with fixed shape such that there is one position which has true pitch across the blades. That pitch is the only one which could possibly be optimal. Every other pitch is by definition sub-optimal.

Likewise, there is exactly one RPM which could be considered optimal, just like with a FPP. That RPM could only be optimal at the optimal pitch. Every other RPM and pitch combination is sub-optimal, by definition.


Now, page 10, first paragraph: They discuss the various modes of pitch/speed control. One of these is constant engine speed and variable pitch. There are several other modes which are fairly standard.

So with reference to "how to use cpp in a boat" you are correct, I have never used one nor seen one used, although I have driven a hovercraft which had one. With reference to "how cpp works in general" I do understand.

Richard, I will not get into an argument with you about how to build or operate a boat. You are a professional with almost as many years experience as I have years of life.

However, when it comes to propellers I have built several and have studied their design. When you or any company tells me that a propeller is optimal across a wide range of conditions, they are either misinformed or they are lying. Or, a third possibility, they have a propeller whose individual blades can change shape in a desired fashion to a new optimal shape while in operation. So far as I have heard, that has never happened and I have never heard a viable theory in how anyone would attempt it.

It is very possible and totally believable that they have optimized a single cpp to be the best compromise for good performance across a wide range of conditions, but that is not what is claimed.

[apex1]

It is very possible and totally believable that they have optimized a single cpp to be the best compromise for good performance across a wide range of conditions, but that is not what is claimed.

Ok, I fully concur! That was a question of (commonly) misused terminology. Compromises are all of the known propulsion systems, a CPP is just one of them and of course not always the "optimal".

[WestVanHan]

Many of the offshore racing unlimited power cats have multispeed transmissions..some have 6 speed sequentials.

[Frosty]

Ok

This is not possible. Once you cast that propeller, it has blades with fixed shape such that there is one position which has true pitch across the blades. That pitch is the only one which could possibly be optimal. Every other pitch is by definition sub-optimal.

Likewise, there is exactly one RPM which could be considered optimal, just like with a FPP. That RPM could only be optimal at the optimal pitch. Every other RPM and pitch combination is sub-optimal, by definition.

It is very possible and totally believable that they have optimized a single cpp to be the best compromise for good performance across a wide range of conditions, but that is not what is claimed.

Absolutely, I just cant be bothered to argue the point these days,--and I dont think I could put it as well as that.

[kroberts]

I need to learn how to figure out when it's just an argument of vocabulary. If I had made my last post first, I would have saved us a whole lot of thread space.

I thought Richard was saying something he was obviously (now) not saying, and that thing was wrong. Richard was using terms which are used by the marketers of propellers, and those marketers were/are overstating their products. If everybody does that, then I can see where the problem started. Not with Richard.

Sorry to everyone for the distraction, and to Richard especially for being such a pain in the ass.

[Fanie]

One question -

Why do you guys argue over something you agree :D

The art of conversation ?

[apex1]

One question -
Why do you guys argue over something you agree :D
The art of conversation ?

We love to do that Fanie, we cultivate that from time to time.....................:p

Ken, no problem, I know we do´nt harm each other.

[marshmat]

OK, now that's out of the way.... :D

So on the continuously-variable transmission issue, let's assume for a moment that we're using a fixed pitch prop optimized for one particular cruise speed and loading state.

That combination of prop, engine and gear ratio will be ideal for that one operating state, but sub-optimal at other speeds and loading states. If we keep the same engine and propeller, can we improve the overall efficiency of the system at off-design speeds by changing the gear ratio? Probably yes. But we generally don't seem to think that the added weight, complexity and cost are worth it.

The question about CVTs thus becomes: Does the ability to continuously vary shaft speed independently of shaft torque bring enough benefits to make up for the substantial complexity and cost, especially given that we generally don't find conventional multi-speed transmissions worthwhile?

[apex1]

The question about CVTs thus becomes: Does the ability to continuously vary shaft speed independently of shaft torque bring enough benefits to make up for the substantial complexity and cost, especially given that we generally don't find conventional multi-speed transmissions worthwhile?

I do not think so.

And btw. a CPP IS a constant variable transmission...............;)

[kroberts]

I'm going to spout off a whole lot of book learning here, but as Richard pointed out some of my sources seem to be tainted by self-interest.

You're looking at a single component of the chain. To go the other direction, you want to look at the entire system. What do you really want out of a propeller-driven boat, to make it go forward?

You want to apply a force to the hull in the direction opposite to that in which you want to go.

With a propeller, that means thrust. To get the most thrust out of a prop, it needs to be tuned for the situation, blah blah blah.

What it comes down to is mass flow. You want to move the largest mass of water possible, backward without wasting any energy. You wanted to take prop tuning out of it, so what's left is something mechanical. Ideally, for a very efficient system, you take a huge amount of mass and accelerate it a very small amount in just the right direction. There are practical limits to that.

You also start with an engine. That engine has a torque curve and a power curve. You want to adapt your drive system to make best use of what you have, and turn it into the mass flow that you want.

That's what the CPP does, and any type of gear box in the middle. Same with any non-gear CVT. Somehow you couple your power as effectively as possible to the water.

The CPP takes the shaft speed from the engine, whatever it is, and adjusts the blades to keep the torque within limits the engine can handle.

A transmission does the opposite, it changes the shaft speed so that the prop's required torque can be had from the engine within reasonable parameters.

Every CVT I know of except one (a flat belt drive such as a conveyor on two conical pulleys) has horrible efficiency (~70%) when compared to a finitely variable transmission like a gearbox (90%+). In some cases there are tricks to minimize that, and in some cases the continuously variable ratio carries an advantage that outweighs the costs in terms of money and lost energy.

The designer's job is to look at the boat, the expected application, and the expected conditions and choose which system makes the most sense.

If you are using a FPP, then what usually happens is you look at the torque/power specs of your engine and the torque/power requirements of your load, and come up with some number of gear ratios which you expect can get you through the day.

The short answer (I could have put this at the top of my post, but otherwise why would you read it?) :D is that if you don't think a multi-speed gear transmission is worth your time, then there is no chance you will shell out the bucks for a CVT.

[marshmat]

We will have to wait and see, since at present I am not aware of any CVTs on the market that would be easily adaptable to marine use. Snowmobile transmissions are too small and not durable enough; they're designed to handle tens of horsepower, maybe a hundred horsepower, with a relatively light duty cycle and low hours/year. The Nissan steel-belt CVT (as seen in the Murano) can handle about 250-300 hp, but again, a light duty cycle is assumed (full power for only a few seconds at a time, and mostly light-load crusing). And it's a complicated, expensive little thing.

I did hear about an infinitely-variable transmission from Ford (I think, but it might have been GM) about ten or twelve years ago (an IVT is a CVT with a geared neutral, ie. can set arbitrarily low output rpm). A very clever design, and IIRC it was supposedly going to handle the 300+ hp engines of the F-series trucks and their SUV brethren, but as far as I know it never made it out of the R&D lab.

In any case, with rapidly growing house loads aboard yachts of all types, and significant effort being put into electric motor development for the car industry, I would not be surprised if the efficiency of electric transmission will improve, and the cost come down, to the point where it may be a feasible option for more types of boats than it is currently useful for. Electric transmission (like hydrostatic, although that is rare) offers the potential to completely decouple prop and engine speed, if we can figure out how to get around the (huge) cost and (relatively high) losses.

[apex1]

One question was not asked here. How often do we change the load conditions, speeds on our average boats?
A bluewater cruiser (motor of course) has a real demand on variable propulsion (which so ever), because he needs just a handful of horses under nice conditions to go faaar away and do that with the given tank capacity. But he needs much more power when in a hurry (to escape weather), or when going uphill in adverse conditions. Any unflexible propulsion, like the conventional, leaves to a noticeable underloaded engine in nice weather.
But there are about 10.000 boats underway on the barefoot routes around the globe, thats about the number of some larger marinas. Joe sixpack does´nt have this problem.

[kroberts]

Richard,

I confess to not having read your reference on electric transmissions, but IMO the thing you describe seems like just exactly the application for it.

[apex1]

Ken, if you want my opinion?!?


My next (probably last) own boat, has a single engine (a very beefy one), and a controllable pitch propeller. And I could afford every other propulsion as well (except maybe "U 235 / Electric").

best regards
Richard

[kroberts]

Richard,

Of course I want your opinion!

Seriously though, the CPP is probably much more practical, but I have a fascination with modern electric transmissions. To the point that I'm contemplating a bicycle with one. I know it will never be practical (especially if I do it myself) but it seems like it would be so neat.

[ancient kayaker]

Interesting discussion; there seems to be a consensus that a constant engine speed gear is wasted on a typical power boat, with perhaps a variable pitch feathering prop for a motor-sailer.

The infinitely-variable transmission is ideal for an auto allowing the engine to run at its ideal speed while the vehicle can adjust its speed over a wide range. An even better arrangement would be one that allowed the engine to run at its optimum power level.

A diesel-electric system allows the primary power source to be located remotely from the final drive element, connected by a copper cable and maybe a computer-controlled electronic transmission. In locomotives it allows the power to be applied to the rails through multiple axles on the locomotive and even through motors on a carriage.

In a large vessel the ability to use multiple, redundant electric power pods and/or bow thrusters has an obvious utility, especially for ferries and suchlike which spend a lot of time docking/undocking and must frequently maneuver in restricted waters.

[marshmat]

The infinitely-variable transmission is ideal for an auto allowing the engine to run at its ideal speed while the vehicle can adjust its speed over a wide range. An even better arrangement would be one that allowed the engine to run at its optimum power level. Some of the carmakers that are using CVTs do have them set up this way, the engine choosing its RPM according to the required power, and the CVT adjusting to suit the speed. Drivers sometimes complain that this is quite weird (the engine will quickly rev up when the pedal is pushed, and will slow down as the car accelerates).

While we're on the subject of variable drives, we ought to at least mention variable-displacement hydrostatic transmissions. They're common on industrial equipment, tractors, ATVs and many other machines, but for some reason are rarely seen on boats. They give the same effect as a CVT or electric transmission (decoupling engine speed from prop speed) and, like electric, allow arbitrary location of the engine room. A well-matched hydrostatic setup should have losses comparable to an electric equivalent. I'm not advocating them as a universal solution, but if unusual transmissions are being considered, they're worth a look.

[WestVanHan]

Just for interest's sake,and not applicable to boats,but CVT s can take a lot of hp.

ie: Skidoo Mach Z 170 hp stock,with minor mods to 220 hp.
Kevlar woven into the belt.
Yes ,I know it's not too heavy.

Mine puts out 340hp,yes for intermittent use :eek:


Willams F1 team tried a twin belt version in '92 (?) and the car was much quicker around a course.Was banned.
In '92 I think F1 cars put out about 770 hp,so 380 a belt


Unless you're racing offshore cats with surface drives,why?

[apex1]

Terry
that >>>>>>>>located remotely from the final drive element<<<<<<< of course is a real advantage (at least for sailing vessels, in a motoryacht I do´nt see much). But we should not forget, that D/E in a motorcruiser starts being attractive when there are a minimum of three different sized generators installed. Due to the fact that a genny runs always at constant speed (AC) you again will fight hughe losses in inefficient operation when you try to operate just two of them! I calculated and recalculated these scenarios again and again and ended up with........................ well, guess.

[kroberts]

Terry
that >>>>>>>>located remotely from the final drive element<<<<<<< of course is a real advantage (at least for sailing vessels, in a motoryacht I do´nt see much). But we should not forget, that D/E in a motorcruiser starts being attractive when there are a minimum of three different sized generators installed. Due to the fact that a genny runs always at constant speed (AC) you again will fight hughe losses in inefficient operation when you try to operate just two of them! I calculated and recalculated these scenarios again and again and ended up with........................ well, guess.

Richard,

I hate to start this up again, but you seem to have a different impression of D/E than I do.

A modern D/E installation, the generator does not run at constant speed. It is throttled according to load required by the inverter.

For as long as I can remember, the D/E train engines changed RPM at will. I grew up near a "slow zone" and I heard it all the time.

The generator's RPM really doesn't matter. It gets converted directly to DC, then is fed into a 3-phase inverter which drives the traction motors. There is absolutely no reason why you need to run the generator at a constant speed, and while I could see the use for 2 generators (one for docking, one for under-way) I really can't see why you would want more, unless maybe if you intend to make slow headway at full throttle on one generator for a long time.

[ancient kayaker]

Ken, I think Richard is thinking of a generator set, in which the engine would normally run at constant speed. A more sophisticated (read bigger) installation such as a D/E your concept would provide more flexibility to allow for optimization, usually of economy.

[kroberts]

Dances with Turkeys,

I'm sure you're right.

I'm convinced that D/E is not economical for anything that small. I'm thinking that if you can't do it right, it will never pay off. Even if you CAN do it right, it won't pay off for years. I don't think a half-assed solution would be rewarding at all.

I kind of wonder if you couldn't make a simple (to use) throttle, where you throttle the engine and the controller simply uses all the available torque as best it can. As I understand it, the locomotives do it the other way, where the throttle powers the motor and the controller sets the diesel throttle based on demand.

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.

[apex1]

Ken, I think Richard is thinking of a generator set, in which the engine would normally run at constant speed. A more sophisticated (read bigger) installation such as a D/E your concept would provide more flexibility to allow for optimization, usually of economy.

Ken I do´nt have impressions I have experience! Or I keep my stupid mouth shut. (well usually)

Of course I was talking AC setup what else? No matter how big. A DC installation is already a hybrid propulsion (if you want at least a little power left after all losses). And than we have the same trouble again, when you do not run the genny diesel at sufficient load you waste just more money.
We should understand direct driven D/E setups (where you have at least two, better three different sized genny´s) they are AC and are very sensible when Hotel loads are high and constant. And the so called hybrid, where we use DC generation and Battery Inverter technology to get our junk running. In both cases we waste much money to save some pennies or to fulfil a mentally ill dream of "green" energy.

I strongly recommend to read the Nigel calder articles at Proboat last year:http://www.proboat-digital.com/proboat/20070607/
and to read "achieving the impossible" from "Victron Energy" (search under whitepapers, downloads)! http://www.victronenergy.com/support-and-downloads/white-papers/
When that is consumed and understood you immediately go and buy a CPP, although that technology is not mentioned there.

Regards
Richard

[kroberts]

Richard,

I assure you I am talking about something completely different than you are. I haven't read much of your articles, but I've read enough to see where they're headed.

On the surface, a 3-phase motor controller driving a generator, yes they are the same.

Your references are, first of all, using batteries. My reference is a diesel locomotive. The only batteries in there are to start the engine. This is mature technology, and it is pervasive throughout nearly every type of industry requiring efficient, highly controlled power from electricity.

Second thing, you are looking at consumer products that MIGHT power an electric golf cart. A decent electric car, for commuting at sub-speed-limit, is going to use WAY more power than your "Achieving the impossible" article references. Using these articles to describe a commercially viable D/E setup

I've been on DIY electric car forums for a while now. (Surprised? Probably not) They generally have more than 100A available for anything that could come sort-of close to highway speeds, and often more than twice that. Your references are quoting 16A. I have a flashlight that probably draws that much.

Stop looking at toys. Start looking at industrial motors, 300 kW and higher, and the industrial 3-phase controllers that drive them. Common sense practicality drives the technology here. Controlling start-up torque, handling power fluctuations and avoiding overloads on circuits started the controller technology on its current path, and robotics finished it. Running something like this from batteries would cost more than the gross national product of a small nation to buy the hardware!

First thing, the advances in motor technology has gone fairly far recently. You can get light weight, strong motors which weigh very little now. You have to pay for them, but they're out there.

Second thing, a serious 3-phase motor controller makes extremely good use of available power, and can control a generator such that the engine wastes very little fuel.

The articles you point to are vapor. It's similar to using hydrogen fuel cells as a power source: Hydrogen does not exist in a high energy state in nature, so it is not a power source at all, it's an energy storage mechanism. Politicians use it as a buzzword to make people think they're doing something important.

Most of the industrial controllers assume line power, but some have controls for a generator. Get them from Siemens or any other respected motor manufacturer.

[apex1]

[QUOTE]I assure you I am talking about something completely different than you are. I haven't read much of your articles, but I've read enough to see where they're headed.

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.

Your references are, first of all, using batteries.
Thats not my reference, thats a article about diesel electric propulsion, I have nothing to do with it.

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


Second thing, you are looking at consumer products that MIGHT power an electric golf cart.

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 looking at toys. Stop talking nonsense!

First thing, the advances in motor technology has gone fairly far recently. You can get light weight, strong motors which weigh very little now. You have to pay for them, but they're out there.

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



The articles you point to are vapor.

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.

[wardd]

i have it, a rotary magazine of several props that can be auto changed for max performance

ok, thats the outline, ill leave the details up to the experts

[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]

[QUOTE=kroberts;293279]


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 :D) 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 :D) 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.

[Frosty]

[QUOTE=Yellowjacket

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.
[/QUOTE]

Not that everything else was'nt relevant or true this comment is interesting.

[apex1]

Not that everything else was'nt relevant or true this comment is interesting.

Thats right Frosty, interesting. But wrong.

[MattZ]

Snowmobiles use a rubber belt with 100+ HP, but they are very high maintenance.

For a diesel engine there`s really little to no difference in efficiency at various engine loads. Gasoline engines have terrible efficiency at part loads, so there is some benefit in this case.

You can very easily achieve continuously variable transmission with a variable displacement hydraulic pump and hydraulic motor. The cost is very prohibitive though.

[apex1]

For a diesel engine there`s really little to no difference in efficiency at various engine loads. Gasoline engines have terrible efficiency at part loads, so there is some benefit in this case.

Quite the opposite is true Matt, sorry.
And as mentioned a thousand times, the cheapest solution is a CPP!

[MattZ]

Quite the opposite is true Matt, sorry.

I'm afraid it's true.

[apex1]

I'm afraid it's true.

Do you call a difference of 100% between underload and full load conditions "no difference"?
I thought all the world knows about Diesel efficiency, obviously not so.


this shows a variety from 210 to 340g/kWh "only"

[MattZ]

Do you call a difference of 100% between underload and full load conditions "no difference"?
I thought all the world knows about Diesel efficiency, obviously not so.


this shows a variety from 210 to 340g/kWh "only"

Now find a similar plot from a gasoline engine and see if you can spot the difference.

[apex1]

Now find a similar plot from a gasoline engine and see if you can spot the difference.

No no, I will not do any effort to make your wrong statement look better!
And I know what I am talking, your statement shows you do not, sorry.

Regards
Richard

[MattZ]

I'm afraid that I'm right and you're wrong. If you looked at similar data for a gasoline engine you would see that the specific fuel consumption doesn't decrease nearly as rapidly as the load is increased.

Even then, the data you posted isn't the correct data to discuss the point I was trying to make, or the concerns of the original poster of the thread.

[apex1]

I'm afraid that I'm right and you're wrong. If you looked at similar data for a gasoline engine you would see that the specific fuel consumption doesn't decrease nearly as rapidly as the load is increased.

Even then, the data you posted isn't the correct data to discuss the point I was trying to make, or the concerns of the original poster of the thread.
What are you trying to tell us here? Please rethink your statement and / or formulation, you are wrong! And everybody knows you are.



For a diesel engine there`s really little to no difference in efficiency at various engine loads. Gasoline engines have terrible efficiency at part loads, so there is some benefit in this case.

Here you contradict yourself! Yes petrol engines have no big difference in specific consumption at different rpm or load. Diesels have!

You can very easily achieve continuously variable transmission with a variable displacement hydraulic pump and hydraulic motor. The cost is very prohibitive though.


We know a continously variable transmission, a CPP. That is the easiest and cheapest way to achieve the requirement. And when you read the thread that becomes quite clear. Though not all know exactly what a CPP is, that´s quite clear too, when one reads the more recent comments.

Even then, the data you posted isn't the correct data to discuss the point I was trying to make, or the concerns of the original poster of the thread.

The concerns of the original poster were not related to diesel efficiency at various loads, as the first post shows, but your comment was, and it was wrong! And remains wrong!
A Diesel engines efficiency varies >extremely< under different load conditions, like it or not!


Regards
Richard

[MattZ]

Here's some enormous change in fuel consumption for a diesel engine between part and full loads.

http://www.manbw.com/files/news/filesof2054/p387_0201.pdf Scroll to page four.

Kind of makes a CPP somewhat insignificant from a fuel consumption point of view.

[TeddyDiver]

Kind of makes a CPP somewhat insignificant from a fuel consumption point of view.
I'm not sure where your logic comes from but..... that pretty much is the point of the advantages of a CPP.

[MattZ]

CPP is typically used to maintain a constant engine RPM for generators, hydraulic pumps, refridgeration plants, or to improve maneuverability, or in gas turbine and steam powered military ships so that they can avoid a reversing gear.

Also in RORO's where quick acceleration and high cruising speed are needed, icebreakers where you need high thrust for breaking ice and still achieve a high speed in open water.

They are used to give you high thrust when needed without over-revving the engine at high cruising speeds, or to allow you high thrust without overloading a smaller engine.

For the most part diesel engines don't vary in specific fuel consumption between different loads. Obvious at 0% load they are 0% efficient, but the difference in specific fuel consumption between say 30% load and 90% load is less than 10% (for a commercial engine. With that and the fact that a CPP is only optimum at one pitch angle, you erase the benefit of a CPP.

Look at the Caterpillar website for some engines and you see the relative flatness of the specific fuel consumption curves.

You won't often see a CPP on an ocean going crude carrier, even the smaller ones with 25,000HP (well within CPP territory) even though they see wide changes in loads running with or into the wind/sea, and fully loaded or minimum ballast.

[TeddyDiver]

:P
Sorry but why you don't study something about the subject instead of mixing up partial knowledge with irrelevant. Whatever anyone else states here won't help you .. or maybe you just Troll or smth..
Teddy

[MattZ]

No offense, but I think I'm a little more studied on the topic than you.

[Yellowjacket]

I'm not sure where your logic comes from but..... that pretty much is the point of the advantages of a CPP.

Teddy,

You need to look carefully at the chart and the scales involved. What this chart shows is that SFC from 30% to max power is only changing by about 5 g/kw-h, which, if this engine is typical of most diesels, best SFC is somewhere around 200 -220 g/kw-h. This shows an swing in SFC that is just about 2.5%. If you go down to really low power (like 20%) you will see a kick up in the SFC curve, but Matt is correct in that in the range from 30 to 100% SFC for diesels is very flat.

[apex1]

No offense, but I think I'm a little more studied on the topic than you.

There I have my doubts! Seriously!

this shows very clear you do´nt have the slightest clue what you are talking!

CPP is typically used to maintain a constant engine RPM for generators, hydraulic pumps, refridgeration plants,

And the table you posted is from a very large crude oil engine and has nothing in common with a yacht Diesel.

Teddy was right, sorry! Study before you contradict.

Richard

[MattZ]

Similar behavior is basically true of all turbocharged diesels.

I just took a look at the C7 non-ACERT C-rating (fairly typical yacht engine, no?), and between 181kW and 46.6kW, BSFC varies by 10%.

So you want to save at best 10% on fuel when you're only burning ~14L/hour anyways? It's going to take many hours before that CPP has paid for itself.

The efficiency of a CPP at other than design pitch is abysmal. Look at what happens when you set the pitch to zero. You can't. Basically the outer part has negative pitch and the inner has positive pitch, and you're burning up fuel to spin water in circles and not go anywhere.

When you're not at optimum pitch one part of the propeller is capturing energy from the water and converting it into rotation, and another part is capturing using that water to push the boat. It's basically a little perpetual motion machine, and you're burning up fuel to make up for the losses in that process.

You can minimize this by using a large hub and short blades, but then you're losing efficiency too.

Within a narrow range of angle variation you can increase efficiency, but it's not wide, and the gains are small.

[baeckmo]

The fuel consumption curves shown previously in this thread are not relevant for a discussion on continuously variable transmissions, of which the CPP is one. They are either showing fuel consumption (FC) at full brake power, or, at best at some "propeller curve" setting. To fully understand the situation, a complete fuel map diagram must be available. For all those, who are familiar with the process, sorry to keep teaching grandma how to make babies, but I hope to make the CPP less diffuse for others.......!

For engine development, the format below (mep as a function of rpm, with constant power and constant FC added) is mostly in use. Mean effective pressure is directly related to torque. The matching process starts in the max power/max speed operating point ("A"), where vessel drag times speed divided with propeller efficiency, represents total power required (let's forget about transmission losses for the sake of clarity).

In this example, we have a 6 cyl 5.5 l direct injected diesel engine, 155 hp intermittent power, and a typical displacement hull. Selecting a 3 bladed Gawn-Burril propeller, BAR 0.5, P/D 0.8, operating at "A" with an advance ratio J ~0.58, we get a prop eta of ~60 %. The effective propeller power at 2200 rpm is then 90 hp. The specific fuel consumption (SFC) is ~167 g/hph, giving a total fuel consumption of 25.9 kg/h. By iteration combining propeller data and hull resistance, a curve for effective propeller power asf of rpm can be drawn; the continuous blue line in the diagram.

The continuous red line above the eff prop pwr (EPP) line is showing constant J (~constant relative slip). As the difference between the red and blue lines increase (for this hull characteristic), the propeller is working at higher advance ratio when the speed is reduced. If we use 2000 rpm for cruising, the EPP will be 66 hp, point "C", and the advance ratio will jump over the top of the propeller efficiency curve to a J of ~0.72, with a prop efficiency of ~0.59 %. The engine power (point "B") will be 112 hp with a SFC of 167 g/hph; total 18.7 kg/h.

Now to the CPP. The hull is requiring 66 effective hp at cruise. Follow the constant hp line for 66 hp (thin blue line) to point "E" at 1400 rpm. Here the propeller is heavier loaded at a J of about 1.0 (=higher slip). This may be achieved by increasing pitch. The optimum pitch for this advance is ~1.2; fixed pitch efficiency 73%. The efficiency of a CPP at non-optimum setting is about 2 % lower. So, with the CPP we have an engine working at point "F" with 93 hp at SFC 159 g/hph; total 14.8 kg/h for the same job!

The example is a "simple" cruising application; if anything like increased resistance (tug, trawling, station holding et c.) were involved, the difference in favour of the CPP would increase dramatically!

Increasing the propeller rpm's (with the original propeller) by changing gear ratio in order to reach the fuel efficient engine range for cruising is not possible, since that prop is operating with ever decreasing J, where the propeller efficiency is falling off, which is one of the reasons CVT's are out of play.

When it comes to non-displacement hulls, the situation becomes completely different, more on that later.

The fuel maps are highly individual for different engines, see examples. Gas engines are just as varying as diesels in this respect; gas turbines a little more "conformal to the type". So, mattZ, you are in deep water where it is wise not to open the mouth too much.......

[apex1]

I'm afraid that I'm right and you're wrong.


Ah, then............. here we go.:D

So, mattZ, you are in deep water where it is wise not to open the mouth too much...

[alan white]

Wait! Diesels taste good PLUS they are good for you!

[Yellowjacket]

Baeckmo's third chart directly supports what both Matt and I have said, that the fuel consumption curve for a diesel being relatively flat, and specifically that the ability to vary speed for a given load via a CVT or a CPP isn't going to buy you more than 10% in fuel consumption at the engine (in the very best case). Prop efficiency is an altogether different matter. I'm just talking about the effect of varing engine speed for a given power on SFC here.

This can be conclusively demonstrated as seen in Baeckmo's third chart, if you look at the 100 hp line (30% of full power) in the SFC map, the SFC can vary from .37 (best) to a max of close to 0.39, (only a 5.1% possible improvement) based on engine speed, and the full power SFC varies from 0.39 to 0.365, again depending on engine speed. Consequently, the absolute maximum that could be gained by a variable pitch prop or a cvt at those speeds is 10% or less. The swing in SFC at any given power curve is less than 10% if you consider a typical propeller demand curve. The need for increasing power at higher engine speed is going to drive a fixed pitch prop up a curve not far from the optimum power line, a bit flatter, but still following the general trend. Between a full power point at 2200 rpm and 350 hp, you are looking at an SFC of 0.39 at max speed and power, and at 1200 rpm at 100 hp the SFC is going to be 0.37. That is a swing of only a bit over 5% and the total swing in SFC over the entire operating range of the engine is 10% (from a best at .352 if you could hit the best op point dead center to .0.39 at max speed and power).

In short, the statement that diesel SFC varies greatly at lower power is simply not supported by the facts. Quit berating the kid when he is right. Matt made a statement that within the range of 30% to 100% power that diesel SFC typically does not vary much more than 10%. I have just shown you that, for the engine 350 hp engine that Beckmo posted the SFC map for, that this statement is absolutely correct. As Matt posted earlier, if you look at the propeller demand curves for the diesels on the CAT site, you will see numerous SFC curves with a kick upwards below 30%. All can agree that is the case, but it only makes a difference at very low speeds and power settings, not where you will expect to operate in the real world.

Bottom line is that a variation of engine speed for a given power will typically only gain you about 5% in fuel consumption, and can't get you much more than 10%, it simply isn't possilbe. That said, propeller efficiency (as Baeckmo) aptly noted) is another story, but if you want to make the case for a CPP or CVT, the gains have to come from the prop and not the engine.

[baeckmo]

Just for the sake of clarity, all three maps shown are for diesel engines, showing typical variation in characteristics between engine individuals. Please note that the subject of the thread is "Continuously variable transmissions". The fixed pitch propeller has a fuel consumption in the example, that is 26 % higher than the CPP in cruising mode!

The diesel MAY have a flat characteristics, but the locus of the min SFC can be far away from a FP propeller operating line, or very close as in the third example. My point here is that you should not use the simple SFC versus rpm diagrams for propeller optimizing.

[TeddyDiver]

Prop efficiency is an altogether different matter. I'm just talking about the effect of varing engine speed for a given power on SFC here.
No you aren't....
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.

..and taking account the subject of this thread you shouldn't either. And besides how can you seriously compare the difference of CPP and FP by load/rpm/power combination that neitherone hardly meets (in the case they do meet it's an intersection of curves).

[Yellowjacket]

No you aren't...

Yes I am and I am doing so to directly differentiate what the effects of a variable transmission are on the engine and what factors contribute to any gain that is or isn't realized. A variable transmission has a potential effect on both the engine and the propeller, and those effects can be broken down and quantified and that is what I was doing.

...and taking account the subject of this thread you shouldn't either. And besides how can you seriously compare the difference of CPP and FP by load/rpm/power combination that neitherone hardly meets (in the case they do meet it's an intersection of curves).

In my earlier post that you have quoted I was addressing the specific reason why a variable transmission isn't required from a torque demand standpoint on higher speed craft. Propeller slip makes any transmission, to a large extent unnecessary. You will note that I specifically said in the post that this was not a particularly efficient way of transmitting power. But in the real world it does't matter since you really don't spend any measurable time at that condition. I don't think anyone on here will disagree with that line of reasoning. What I was simply trying to do was explain why props are different than wheels on a car in terms of the need for gearing.

The thread is exactly about continuously variable transmissions, of which CPP's are a subset, and the discussion has moved on from a discussion as to why do you need a transmission at all, to one of addressing the potential effects of CVT's on overall propulsion system efficiency. One of the express reasons for a variable transmission is to optimize the engine and attempt to achieve an improvement in engine SFC over the range of operating conditions. While that type of logic is very applicable to spark ignition engines in land vehicles, which operate at very low power percentages at cruising speeds, and have very poor part power SFC, it does not make much sense in a marine environment, where the best speed/efficiency characteristic of a diesel is more closely related to a prop demand curve.

Consequently you cannot achieve a significant gain in fuel consumption from the engine standpoint with any kind of variable transmission. As clearly pointed out, the effects of a CVT on engine efficiency is typically less than 5% and is no more than 10% under all conditions for the example noted. The specific fuel consumption of the engine isn't the factor here, in a nutshell, it is the prop.

I wasn't attempting to compare CPP and FP systems, they are clearly different and each has advantages and disadvantages depending on the needs of user, the speeds/loads and power requirements. I was simply addressing the potential effects of efficiency of a diesel at off design conditions that seemed to be a point of contention in a couple of previous posts so that we can get on to more substantive discussion.

[TeddyDiver]

it does not make much sense in a marine environment, where the best speed/efficiency characteristic of a diesel is more closely related to a prop demand curve.
This is exactly the point where you lose the track.. With CPP (and with any true variable transmission) that curve is not where you think it is.. becouse there isn't any curve instead it's wide field where the best possible combination can be selected. Some prefixed limitations there's, blade area for instance, but thats a characteristic belonging more in the same category with the hullform you playing with.
I think you have more experience of planning speeds over displacement so it's understandable to have somewhat different conception of this matter, but the world is still in displacement with knots not planning at mph :D

[wardd]

Wait! Diesels taste good PLUS they are good for you!

and they're fun to paint and listen to

[Yellowjacket]

This is exactly the point where you lose the track.. With CPP (and with any true variable transmission) that curve is not where you think it is.. becouse there isn't any curve instead it's wide field where the best possible combination can be selected. Some prefixed limitations there's, blade area for instance, but thats a characteristic belonging more in the same category with the hullform you playing with.
I think you have more experience of planning speeds over displacement so it's understandable to have somewhat different conception of this matter, but the world is still in displacement with knots not planning at mph :D

I doesn't matter where you go on the map, the gain can't be any more than 10% in engine efficiency with any kind of CVT. That's all there is worst case.

In the efficiency assessment I was making and comparing the percentage gain, you can go anywhere on the map and at best get a 10% difference between best SFC and worst SFC. While a planing hull will have a parabolic (with a hump) load/speed curve, and a displacement hull will have a hocky stick curve, it doesn't matter.

The effect I was describing, while more applicable to planing speeds I've tried to sketch in both a displacement (red lines) and a planing (blue lines)example on Baeckmos chart. The solid lines would be a worst case, optimized for maximum power at higher speed and might be more applicable to the planing hull, where you would prop the boat to have a higher engine speed to help you get up on a plane faster. The other (dashed) lines are optimized for a lower engine speed and power as might be applicable to a displacement hull. These aren't by any means difinitive, but you get the basic idea and it will become apparent that the gains in engine efficiency are small because the hull loading, even for a displacement hull is basically going to ride along the efficiency islands and not cut across them. Like I said, worst case it is 10%. Real world, look at the difference at the displacement hull at a 140 hp crusie and you are talking the difference between a .36 and a .375 SFC, or more like 2.5%. If you optimize at a lower speed the differences are even smaller.

You have to trade cost versus performance benefits, and, as far as the engine is concerned there isn't much reason for a CVT in either displacement or planing craft.

[Fanie]

Originally Posted by alan white
Wait! Diesels taste good PLUS they are good for you!

and they're fun to paint and listen to

If you plant them they also grow faster than petrols :D

[wardd]

If you plant them they also grow faster than petrols :D

and rabbits dont eat them

[hoytedow]

...unless they're steamed.:D:D:D

[wardd]

rabbits like their veggies/diesels raw

[hoytedow]

True. My bad.

[apex1]

Well, lets make the things clearer.
The thread was about CVT, right?
There is only one proven, cheap, and reliable system available at present: a CPP! No doubts ok?
Engine efficiency (and the marine world talks engine and Diesel in the same breath) is varying under different loads ok?
The graphs shown here by Baeckmo and me had a bandwidth from above 20% to above 60% in specific consumption between optimal and worst! Not 5 to 10% !!! At least my calculator says so when 160 to 200gHp and 210 to 340gHp are the given figures.
But what is engine efficiency? The optimal ACHIEVABLE figure right?
With a fixed prop we cannot operate a Diesel at optimal consumption points under different loads. There is ONE point and that was it. Above or below we loose efficiency in consumption.
BUT consumption is by far not all. Being ABLE to operate under certain conditions is more likely the point to adress.
Leaving the planing speeds and looking just at the displacement world, where the CPP is common, we have several sensible reasons.
A displacement yacht of say 500 tonnes and with a installed power of 2x 500 hp (to make calc.s easy), goes 13kn max. and say 11kn at 80% power setting. The max. range is thought to be 3000 miles at 9kn! Ok?
Ah, but at that max. range only 120hp is needed for propulsion.
So now you clever guys tell me what is a efficient way to achieve a long engine life, a efficient cruising speed and a minimum service bill?
1000 hp set at 12% ??? The service bill will make you laugh....







...from fear and fury

[wardd]

coming at it from a different angle

i have a john deere diesel tractor with a hydrostatic transmission, at first i was reluctant to run it at high speed only used engine speed that gave me the travel speed i wanted

after a while the diesel started running raggedly

now i run the engine at rated rpm and use the transmission for speed control

engine now runs much smoother

seems diesels like to spin

[TeddyDiver]

seems diesels like to spin
Some diesels do.. not familiar with John Deere, but Toyota 2.44 is one I'm familiar with and it belongs into same category. Not good for marine engine..

[brian eiland]

Looks like some interesting discussions have occurred in this subject thread that might well be applied to this "New Age Trawler/Motorsailer; Kite-assisted PowerYacht" I brought up in this subject thread (http://www.boatdesign.net/forums/boat-design/new-age-trawler-motorsailer-kite-assisted-poweryacht-20319.html).

I've not had time to go thru this subject thread throughly yet, but to remind myself to do so, I hereby contribute this posting, and ask some of the more knowledgeable participants to suggest what form of propulsion package they might suggest would be most applicable for this vessel concept.

An excerpt from that vessel posting:

Back to those design concept drawings by Humphrey’s (attached PDF). I can fully imagine a scaled-down version of this tri-hull design, in the 65-70 foot range...

The power would be a single main engine sized to develop the vessel’s desired top speed, and it could transmit this power by conventional shaft/prop arrangement, or with a azimuthing Volvo IPS dual prop unit, or via a retractable azimuthing Rim-Drive prop unit as I included on my latest dynarig motorsailer design.
1) Volvo IPS : http://www.yachtforums.com/forums/yacht-reviews-feature-stories/7467-world-debut-volvo-pentas-new-ips-750-850-a.html
2) Rim Drive : http://www.yachtforums.com/forums/te...ropellers.html (http://www.yachtforums.com/forums/technical-discussion/3961-rim-driven-propellers.html)

Supplementing this single main engine would be a single DC diesel/electric power unit to provide for:
1) Ships electrical requirements
2) Slow speed operation by electric (wing) motor belted to main prop shaft
3) Maneuvering thrusters as required depending upon azimuth capabilities of main prop.

The entire ship would be powered by only two engines, basically sized to provide:
1) Full main diesel power, unimpeded by interceding diesel/electric conversion
2) Slow speed operation and ship’s systems via the smaller diesel/electric unit
3) ‘Twin power’ emergency backup as either engine can run all gear
This configuration more ideally meets the latest thinking for the new diesel/electric DC technologies onboard smaller vessels. Alternatively, two identical diesel/electric plants might be sized such that in combination they would supply the max power required of the vessel, and half power for lesser times.

...or maybe a CPP prop that would feather,
...and maybe driven by a chain belt drive leg such as THIS (http://www.yachtforums.com/forums/15453-post14.html)

[FAST FRED]

" Alternatively, two identical diesel/electric plants might be sized such that in combination they would supply the max power required of the vessel, and half power for lesser times."

While it might not give the "bragging rights" of all this complexity

anyone wanting to create an efficient cruiser will find the parts readily aviliable at a marine scrap yard.

A US Navy landing craft coupled two engines to a single shaft since WWII.

Usually 2x 6-71 , can be had for about $6000 Navy rebuilt.The light duty Cummins are more modern but shorter lived.

The 6-71 might be swopped for a 2 or a 3 on a small boat that cruises on 20 -60hp, or left in place and simply used for 150hp per engine , as needed.

The bellhousing is SAE 1 so most any engines could be used , although a 6-71 and 3-71 would allow lots of parts canabalization for the offshore cruisers.

FF

[brian eiland]

...A US Navy landing craft coupled two engines to a single shaft since WWII.
FF
I do realize these type of two engines on one shaft possibilities, but then where do you get your electrical power for the ship, the kite winching, the bow thruster, the dive compressers etc, etc. You would need to add another generator plant...remember I said two engines for the entire vessel. Thats why I included at least one diesel/electric unit in the combination of the two.

For the best effeciency (in a higher fuel price world), those paired engines on one shaft would require a variable pitch prop.

[FAST FRED]

For the best effeciency (in a higher fuel price world), those paired engines on one shaft would require a variable pitch prop.

Perhaps , it would really depend if the power of identical engines were needed, or if a large /small combo would suffice.

The small engine could easily provide power for most requirements .

The DD and many other more industrial engines have built in geared PTO's , most rated for 30- 45 hp cont output.

Plus the triple pully on the crank at another 40-50HP .Propulsion and or house.

A bus alt is 24V and 300A , enough for modest house loads with a Trace 4024 , 4KW , which can be ganged to 8KW.

The usual PTO will run an off the shelf Hyd pump, with or without clutch, as found on working fish boats.

FF

[mikeharwood]

Hello,

I just came upon this thread and thought that the Torotrak IVT might be suitable for use on boats. Then again I could be completely wrong :confused:

Mike

http://www.boatdesign.net/forums/propulsion/torotrak-infinately-variable-transmission-20353.html

[marshmat]

Torotrak transmission - certainly a possibility. If they can get it to work reliably in long-term use, ie. 10,000+ hours between major servicing, it would likely be an excellent alternative to a conventional geared transmission for road vehicles, and there would be cases where it would be a good alternative to a conventional gearbox in the marine world.

If the transmission losses can be made comparable to those in a conventional planetary or 2-shaft gearbox, at not too big a cost premium, an IVT could very well become a viable option for some boats. Perhaps not so much for those that always cruise at one speed, and you'll never convert die-hard CPP lovers, but for some boats- like these "fast trawlers" (wtf?) that are popping up all over the place- a fixed prop and variable transmission might be useful.

A fully integrated installation would communicate with the engine's computer; ie. the throttle lever would directly control prop RPM, and the details of what combination of IVT setting and engine throttle setting would give the most efficient operation and a properly loaded engine would be handled by the computers.

Of course, there are those more traditional types who would prefer a direct mechanical linkage between the captain's hand and the variator pistons.

Various forms of this thing have been going around for quite a while- if I recall correctly, Ford was experimenting with a similar IVT in the mid-90s. From what I understand, one of the big problems with toroidal variators is the potential for greatly accelerated wear if there is any slippage of the variator rollers. Torotrak is saying that they have a specialized "traction fluid" oil, whose viscosity is highly pressure-dependent, to resolve this issue.

[Brian@BNE]

Ok, old thread I know.

But, does anyone know if Torotrak (or similar products) referred to above are available for 20-50 HP range, and what the prices are? What is the efficiency of the Torotrak?

Proposed application is for motor-assisted sailing, where part of the effective thrust is from the sails and therefore the prop demand power is lower than would otherwise be the case for given speed. A fixed gear 2-3 speed might be OK. Just wondering if the last couple of years has changed things - car transmissions seem to have advanced quite a bit in that time, any good developments in marine tranny's?

A CPP would be a great alternative, but I don't think they exist at these low power levels. And trying to swing a 750mm Helseth designed for min 200kW (their smallest?) will probably mean some inefficiencies, not to mention a disproportionate cost.

[Brian@BNE]

This NSK device for cars, announced a couple of months ago could be ok. They claim 97% efficiency. Power range should be about right?

http://www.nsk.com/company/presslounge/news/2011/press111129.html

[TeddyDiver]

the Torotrak IVT might be suitable for use on boats.
I can see one basic flow in this concept and it's because fixed pitch propeller has so limited operational range due the power curve shape and cavitation issues at high revs. That is just IMHO..

[Brian@BNE]

Teddy
The idea is to use as large a diameter as possible, turning relatively slowly. The prop would then be pitched to just give full rpm of engine, as normal. So the issue becomes loss of prop efficiency at lower rpm, also normal.

When motor-sailing, the CVT would enable the diesel to run, say, just above fast idle, but be loaded enough to operate within an efficient exhaust gas temperature range and hopefully good BSFC.

I don't know whether fuel savings will give a reasonable payback period for the tranny, but the ambiance in the boat with minimal noise and vibration whilst making good speed when passage-making is one benefit. For a boat that doesn't do many miles it would not be worth considering.

The other benefit is that on a cat the other hull can have an electric drive, using power from the one running diesel. Its a diesel-electric drive with a difference - one hull is diesel, the other is electric! For redundancy, both hulls will have a diesel, but they can be of different sizes, providing further avenues for fuel efficient passage-making.

Of course there are issues. Apart from complexity, the CVT tranny could well be heavier than a fixed gear one, and then there is the weight and size of the electric motors and drive controllers etc. Whether it would make sense on a 40-something-ft cat is still to be worked out.

[TeddyDiver]

The weight difference isn't so much an issue with motorsailors and that's about the best possible boat to use with a transmission like this. The limitations with this drive train means that it's at is best when the prop is drived at more or less constant speed just varying the engine rpm depending how much thrust the sails give for the boat.
BR Teddy

[brian eiland]

Teddy
The idea is to use as large a diameter as possible, turning relatively slowly. The prop would then be pitched to just give full rpm of engine, as normal. So the issue becomes loss of prop efficiency at lower rpm, also normal.

When motor-sailing, the CVT would enable the diesel to run, say, just above fast idle, but be loaded enough to operate within an efficient exhaust gas temperature range and hopefully good BSFC.

I don't know whether fuel savings will give a reasonable payback period for the tranny, but the ambiance in the boat with minimal noise and vibration whilst making good speed when passage-making is one benefit. For a boat that doesn't do many miles it would not be worth considering.

The other benefit is that on a cat the other hull can have an electric drive, using power from the one running diesel. Its a diesel-electric drive with a difference - one hull is diesel, the other is electric! For redundancy, both hulls will have a diesel, but they can be of different sizes, providing further avenues for fuel efficient passage-making.

Of course there are issues. Apart from complexity, the CVT tranny could well be heavier than a fixed gear one, and then there is the weight and size of the electric motors and drive controllers etc. Whether it would make sense on a 40-something-ft cat is still to be worked out.
Sort of something along this idea....
The power would be a single main engine sized to develop the vessel’s desired top speed, and it could transmit this power by conventional shaft/prop arrangement, or with a azimuthing Volvo IPS dual prop unit, or via a retractable azimuthing Rim-Drive prop unit as I included on my latest dynarig motorsailer design.

Supplementing this single main engine would be a single DC diesel/electric power unit to provide for:
1) Ships electrical requirements
2) Slow speed operation by electric (wing) motor belted to main prop shaft
3) Maneuvering thrusters as required depending upon azimuth capabilities of main prop.

The entire ship would be powered by only two engines, basically sized to provide:
1) Full main diesel power, unimpeded by interceding diesel/electric conversion
2) Slow speed operation and ship’s systems via the smaller diesel/electric unit
3) ‘Twin power’ emergency backup as either engine can run all gear
This configuration more ideally meets the latest thinking for the new diesel/electric DC technologies onboard smaller vessels. Alternatively, two identical diesel/electric plants might be sized such that in combination they would supply the max power required of the vessel, and half power for lesser times.

Only two engines and no conventional sailing rig should make this a more affordable vessel, both in construction, in maintenance, and in operation. However the SkySail kite arrangement will probably more than offset the conventional sailing rig in cost. Possibly a less expensive alternative to this ‘brand name’, with less computerization could be found (no integrated weather/navigation features, etc). Light-weight construction would be desirable but not necessary. Third world hull construction materials are a possibility.

I’ll call it a KiteSail Motorsailer for now.
....comments, suggestions
http://www.boatdesign.net/forums/boat-design/new-age-trawler-motorsailer-kite-assisted-poweryacht-20319.html

[Brian@BNE]

Brian
Similar concepts for economy and flexibility. But use conventional sailing rig also. Really trying to drive both props in a cat with just one engine, and minimize the inefficiency of small-scale diesel-electric configuration noted by Hybrid-Marine. See their paper, attached, comparing conventional drive, diesel electric and serial or parallel hybrid drives.

In effect the ideas I put above is the Hybrid-Marine set-up, but with something like the NSK toroidal variator instead of their fixed ratio PRM 150 gearbox. The variator is a key part of the overall system efficiency for a cat installation.

[Boston]

next question is cost

whats it cost to gain what in efficiency

and whats that translate to in fuel savings and how long does that take to pay itself back compared to the added complexity and weight of the hybrid system?

on that 35 I'm playing with two new Kubota engines cost 4200 each, and two multiple v belt reduction arrangements + 2 clutchs seems so much cheaper than all the hybrid stuff you'd have to put in 10xthousands of miles a year to hit pay back time.

[Brian@BNE]

Boston
yes, cost will be an issue. I'm not into VW at 40k either. I wouldn't want to think what they cost in AU if that's the price you can get. And the Hybrid-Marine prices are scary for their electric stuff, and to boot they are in GBP.

Not sure what Catbuilder came up with as far as final config and costs were for his electric options. That thread of his went cold a bit after he clammed up thinking he'd invented a retractable drive or something, but wouldn't share it on the forum.

I've emailed NSK for dimensions, weight and input power range for their new toroidal variator. No doubt they'll need a significant car manufacturer to sign up before the things are commercially available, and only then would talking to them on cost make sense.

So yes, I'm probably dreaming with the stuff I've put here. A bit like your pencil/eraser story on your 35ft design. By the way, just buy something the right length, cut off the superstructure and put yours on. Bound to be cheaper. My guess is used boats are 30 cents in the dollar compared to new build right now.

I'm OK with your 'junkyard wars' approach , but would want a system that provided reverse quickly and reliably. V belts would be OK with a CPP, but so far I can't find any CPP's in the size we'd be using (40-46ft sailing cat to be re-powered in my case). To me the 'junkyards' worth fossicking in are the farming/agricultural ones. Sure they use v belts in some gear, but there is a lot of other stuff at right power ratings that might be able to be used differently to original purpose. Cost and efficiency are words that mean a lot to those folks too.

[Boston]

go to any agy supply and look at PTO shaft accessories, a dime a dozen and all well within the 40 hp and 100 ft/lb range we'd be needing. They got some real nifty stuff and its all continuous duty. You can find the stuff used by the tens of thousands.

[whitepointer23]

The CVT, invented by Huub van Doorne 30 years ago and improved numerous times, never got wide acceptance because the metal belt is very difficult to produce, especially when a lot of horsepowers are involved.
A few small Japanese cars use this system, the patented belt being supplied by the Dutch company. They still seem to be experimenting with larger ones.

the nissan merano is a large vehicle with a powerfull engine driving a cvt.

[BATAAN]

I can see one basic flow in this concept and it's because fixed pitch propeller has so limited operational range due the power curve shape and cavitation issues at high revs. That is just IMHO..

I've been pushing water with a controllable pitch SABB 30 hp for many years and would feel very handicapped going to a fixed pitch prop. When approaching a dock in the wind with my 40', 23 ton yawl, I reduce pitch but not RPM until we are just crawling along, but still under control. Usually I can lay the boat alongside and just drop the lines on the cleats from the deck. Also, at sea when motorsailing or motoring, the load is always properly adjusted by pitch and throttle. This setup seems to be exclusively a European thing, like medical care and parental leave, so I won't hold my breath to see it built or used here, too sensible.

[jak3b]

Hey,This is Amuraka it doesnt have to make sense just money.

[Brian@BNE]

Someone who can supply CPP in the 50-200 HP range would really make money.....

[BATAAN]

Some current manufacturers of CP systems.
The rest of the world is leaving us behind.
No surprise since we're headed back to the 1880s as fast as we can go. Screamingly afraid of the future and science is the way we are viewed by people in other countries.
I have friends in Europe and a brother-in-law in China and hear a lot about how dense we are and unwilling to do anything sensible.

[TeddyDiver]

And more:
http://www.nogva.no/?CatID=1191
http://www.westmekan.com/propeller-equipment/
http://selfa.no/fremdriftsanlegg-med-vribar-propell/

[Brian@BNE]

And more:
http://www.nogva.no/?CatID=1191
http://www.westmekan.com/propeller-equipment/
http://selfa.no/fremdriftsanlegg-med-vribar-propell/

Thanks Teddy, some good links there.
1. Cant find any sizes for Nogva
2. Westmekan give a range of dimensions, except prop diameter but from shaft size etc it looks as though their sailing CPP range could be in the right size!
3. Selfa appear to carry/supply from a range of manufacturers, possibly some are in the low power/sailing boat range

[Brian@BNE]

Some current manufacturers of CP systems.
The rest of the world is leaving us behind.
No surprise since we're headed back to the 1880s as fast as we can go. Screamingly afraid of the future and science is the way we are viewed by people in other countries.
I have friends in Europe and a brother-in-law in China and hear a lot about how dense we are and unwilling to do anything sensible.

Hmm, interesting. Finnoy only shown down to 1000 mm size, P26. But Marine Systems (UK) Ltd, who source from Finnoy, show a P18 down to 650 mm. This could well be just the right size!

Once I have got the boat and can advise the required input details, a quote from these folks could be the way to go. No doubt I'd want to be sitting down when i got their reply, but still......

[TeddyDiver]

Anyway the SABB gearboxes Selfa sells in the small end are the right size. The down side is that they have too limited range for pitch control for sailboats so either you have from FWD to AST (without feathering) or FWD to feathering (without astern).
Westmekan has the right product for sailboats but they are lazy to answer any questions so some serious telephone terrorism migh be needed to get some response. Their product is not too cheap either, if I recall right EHWS with 40mm shaft was about 70000NOK
BR Teddy

[BATAAN]

Been using the SABB 28 years and the blade area is small enough on the 2 blade that even flat at neutral pitch there is very little drag if you align it with the strut.
All the effort to get a fully feathering prop is really not worth it.
Several propellers do the CVT thing by changing their pitch to reflect the load automatically and if you insist on full feathering, this is the cheapest way to go and get CVT effect.
The Autoprop seems to be the most successful at what you are looking for, but check out Bruntons complete line.
http://www.bruntons-propellers.com/Autoprop/Autoprophome.htm