Low RPM cruise

[GaryBode]

You all should become physics professors.

[Kenomac]

Originally Posted by a64pilot

It is simple physics, and its true for airplanes, cars, boats and I’m sure trains.
If you want to make something move, you have to expend energy, if you want it to move faster, You expend more energy than you get in a relative increase in speed.
It’s funny though, in every thing there is people who want to think their is a sweet spot, in airplanes many are convinced if they climb to a higher altitude and then slowly descend to assigned altitude speeding up as they descend that they will end up at a higher stabilized airspeed, an enormous number of people believe that, it’s even often taught.
It’s a complete myth though, no truth to it at all.

It’s like the stopped prop thing, many if not most are sure that a stopped prop is less drag than a freewheeling one. I did, until proven different. It’s funny though that many, even when they see the testing, still won’t believe it.

Originally Posted by Dockhead

The relevance is this: your Toyota Corolla, just like any car, just like any airplane, and just like any displacement hull vessel, is subject to the same basic principle that resistance through air or water goes up exponentially with speed, requiring more power disproportionate to the increased distance covered at a higher speed.


"More power" = more fuel. That means fuel mileage falls with speed. There are very few and very narrow exceptions, some of which have been mentioned already.

OK a question for the two of you..

64pilot your Yanmar is around 36 years old if I remember correctly? And Dockhead, Your Yanmar is around 20 years old.. correct?

Do the two of you honestly believe that diesel technology has basically stood still over the past 20-35 years? Nothing new has been done to increase mileage or efficiency, that time has basically stood still in your minds.

Well, our diesel is 8 years old and I can tell you from first-hand knowledge, that diesel tech has been on the move and our 2010 Perkins 185hp turbo diesel engine is unbelievably efficient and able to probably attain greater fuel efficiency than either of your two older engines. Just look around the EU over here... turbo diesels in most cars getting unbelievable mileage 50-60mpg is common unlike in the US where they’re busy screwing around with batteries and hybrids.

Things have changed and maybe the old school graphs are no longer applicable.

[Dockhead]

Originally Posted by Kenomac

OK a question for the two of you..

64 your Yanmar is around 36 years old if I remember correctly? And Dockhead, Your Yanmar is around 20 years old.. correct?

Do the two of you honestly believe that diesel technology has basically stood still over the past 20-35 years? Nothing new has been done to increase mileage or efficiency, that time has basically stood still in your minds.

Well, our diesel is 8 years old and I can tell you from first-hand knowledge, that diesel tech has been on the move and our 2010 Perkins engine is unbelievably efficient and able to probably attain greater fuel efficiency than either of your two older engines. Just look around the EU over here... turbo diesels in most cars getting unbelievable mileage 50-60mpg is common unlike in the US where they’re screwing around with batteries and hybrids.

Things have changed and maybe the old school graphs are no longer applicable.

Well, maybe! Let's see the specific fuel consumption curves. If there is a dramatic increase in efficiency, more than the hull resistance curve, I'll be very happy to be shown to be wrong and thus learn something.


In one of the linked articles is a further link to a hull resistance calculator you can use for your boat.




And what is the maximum efficiency of your engine? Mine is about 167g/hp/hr. Is your engine common rail? Non-common rail engines have not been dramatically improved in efficiency since 2001 when my engine was made, but common rail engines are indeed a big leap forward and different in some ways.

[Kenomac]

Originally Posted by Dockhead

Well, maybe! Let's see the specific fuel consumption curves. If there is a dramatic increase in efficiency, more than the hull resistance curve, I'll be very happy to be shown to be wrong and thus learn something.


In one of the linked articles is a further link to a hull resistance calculator you can use for your boat.




And what is the maximum efficiency of your engine? Mine is about 167g/hp/hr. Is your engine common rail? Non-common rail engines have not been dramatically improved in efficiency since 2001 when my engine was made, but common rail engines are indeed a big leap forward and different in some ways.

I bought the boat, monitored the fuel consumption over several months and a thousand miles, and I was amazed. You’re going to have to do your own homework on this one if you don’t believe me.

Time moves on, progress is made, technology doesn’t stand still. There’s really nothing more to add.

[a64pilot]

Originally Posted by CatNewBee

Indeed there is a sweet spot, you have a non-linear curve regarding torque in combustion engines. You need some rpm to become efficient, but it is not at maximum power / maximum rpm.

Also the resistance of air and water are non-linear to the speed, it rises exponential and goes to infinity at speed of light even in vacuum.

Yes, there is a sweet spot for the engine, it’s the “bucket” on the BSFC fuel graph.
However it’s way more than overcome by the drag if the vehicle / vessel it’s pushing or pulling.

[a64pilot]

Common rails are more efficient, but only slightly, this may be due in part to tighter emissions requirements that they can meet.
I don’t know how much if any more efficient they could be made if emissions weren’t a consideration, but I bet it’s not much.
I wish there was a big efficiency jump in some kind of engine, unfortunately advances are made one or two percent at a time.
However over a fleet size of millions, one or two percent is significant.

Oh, and superheated air into the intake is a Nono. There are after coolers specifically to reduce intake temp, the reason is air density, what a turbo accomplishes is it puts more air into a cylinder. If you heat and expand that air, it is detrimental, you make less power with hot induction air.

What a turbo does efficiency wise is harness waste heat, if you measure the exhaust temp before and after the turbo, you will find a significant drop in temp, this is because energy has been extracted form the exhaust and fed back into the engine if you will, and this does slightly increase efficiency.


However a very good point has been brought up, if we sailors want to learn how to motor most efficiently, maybe we ought to listen to our Trawler brothers, cause I bet they have that down to a science as it’s their only means of propulsion.

[Dockhead]

Originally Posted by Kenomac

I bought the boat, monitored the fuel consumption over several months and a thousand miles, and I was amazed. You’re going to have to do your own homework on this one if you don’t believe me.

Time moves on, progress is made, technology doesn’t stand still.

I have done my homework, and I shared it with the forum in this thread. Quite a lot of homework. Furthermore, I have a $1500 fuel flow metering system and have measured my own fuel consumption at different speeds. My measured fuel consumption corresponds to all of the liters/mile tables which other people have posted in this thread, and also the one which was presented in the paper I linked to -- in all cases, best fuel consumption occurs at lowest measured speed, and goes down steadily as speed increases.



You cannot measure fuel consumption accurately the way you describe. You are not maintaining the same speed over the whole tank.


Let's see your specific fuel consumption curves -- that may give some insight. Or tell me the engine model and I'll look it up myself. Is it a common rail, and thus dramatically different from the diesels of the rest of us? That would make it interesting.

[Kenomac]

Originally Posted by Dockhead

I have done my homework, and I shared it with the forum in this thread. Quite a lot of homework. Furthermore, I have a $1500 fuel flow metering system and have measured my own fuel consumption at different speeds. My measured fuel consumption corresponds to all of the liters/mile tables which other people have posted in this thread, and also the one which was presented in the paper I linked to -- in all cases, best fuel consumption occurs at lowest measured speed, and goes down steadily as speed increases.



You cannot measure fuel consumption accurately the way you describe. You are not maintaining the same speed over the whole tank.


Let's see your specific fuel consumption curves -- that may give some insight. Or tell me the engine model and I'll look it up myself. Is it a common rail, and thus dramatically different from the diesels of the rest of us? That would make it interesting.

Please show me what a “$1500 fuel flow metering system” looks like. I’d sooner put $1500 worth of diesel in our tanks than buy such a thing.

Here’s what an incredibly efficient Perkins Sabre looks like .

[Dockhead]

Originally Posted by Kenomac

Please show me what a “$1500 fuel flow metering system” looks like. I’d sooner put $1500 worth of diesel in our tanks than buy such a thing.. . .

Here you are:



https://www.maretron.com/products/ffm100.php








It's part of our NMEA2000 network, which has many different functions.


It will read out liters/mile directly and so will give you instantaneous directly measured information on the subject of this discussion.

[transmitterdan]

Originally Posted by a64pilot

You guys don’t want to believe actual data, but here it’s posted.
BTW Sailorboys motor isn’t a Turbo so much for that.
It follows exactly along with automobiles, the faster you go, the more fuel you burn per distance travelled. This graph is meant to show difference in MPG for tire pressure, but it also shows exact fuel mileage per speed, and it’s a US government EPA study, not some kids who post on YouTube. As you can see, there is no sweet spot for cars, even though you ask the average guy and they are convinced there is.Attachment 178421

Physics isn’t just a good idea, it’s the law

Try extending that curve all the way down to 0 MPH. You will cross over a peak at about 30-40MPH. It isn’t a simple always decreasing curve.

[Kenomac]

Originally Posted by Dockhead

Here you are:



https://www.maretron.com/products/ffm100.php


Attachment 178440


Attachment 178441


It's part of our NMEA2000 network, which has many different functions.


It will read out liters/mile directly and so will give you instantaneous directly measured information on the subject of this discussion.

Nice. But like I wrote, I’d rather put $1500 worth of diesel in the tank than buy such a thing.

BTW: Why would you buy a fuel delivery monitoring system like that and not a fuel polishing system?

[sailorboy1]

Originally Posted by Dockhead

and Sailorboy, but I know for sure that you are simply mistaken about this. .

I've never been call a liar so politely so many time in one thread

Bet people don't really understand that are is a lot of efficiency factors to consider. I use to design pump systems and people always assumed it it was better to pump slower because there would less head loss friction. But, LOTS of times it wasn't because you might lose 30-50% of efficiency between the pump and motor running so far below their most efficient point. An engine driving a propeller is the same thing.

Now please stop calling be a liar about my own direct years of operational knowledge about MY boat!!!!

[Dockhead]

Originally Posted by sailorboy1

I've never been call a liar so politely so many time in one thread

No one ever called you a liar. In this particular case, you are simply mistaken, and there is no shame in that. I am mistaken as often as you or anyone else is, and I am generally grateful to those who bring me new knowledge that helps me see that.

[Kenomac]

Originally Posted by a64pilot

Common rails are more efficient, but only slightly, this may be due in part to tighter emissions requirements that they can meet.
I don’t know how much if any more efficient they could be made if emissions weren’t a consideration, but I bet it’s not much.
I wish there was a big efficiency jump in some kind of engine, unfortunately advances are made one or two percent at a time.
However over a fleet size of millions, one or two percent is significant.

Oh, and superheated air into the intake is a Nono. There are after coolers specifically to reduce intake temp, the reason is air density, what a turbo accomplishes is it puts more air into a cylinder. If you heat and expand that air, it is detrimental, you make less power with hot induction air.

What a turbo does efficiency wise is harness waste heat, if you measure the exhaust temp before and after the turbo, you will find a significant drop in temp, this is because energy has been extracted form the exhaust and fed back into the engine if you will, and this does slightly increase efficiency.


However a very good point has been brought up, if we sailors want to learn how to motor most efficiently, maybe we ought to listen to our Trawler brothers, cause I bet they have that down to a science as it’s their only means of propulsion.

Actually, we need a good thread on motor-sailing. Maybe in two weeks I’ll get one started when I’m back in the sates.

[Dockhead]

Originally Posted by Kenomac

Nice. But like I wrote, I’d rather put $1500 worth of diesel in the tank than buy such a thing.

BTW: Why would you buy a fuel delivery monitoring system like that and not a fuel polishing system?

Sure. Everyone has his own priorities, and that's fine. My electronics system was a really fun project some years ago that I sank quite a bit of money and time into. I have gotten a great deal of enjoyment out of the system; it has some awesome functions. I also had a great deal of fun designing and installing it. There is nothing economically rational about it; like boats in general.