Fuel Economy Monitoring?

[markpierce]

...The longest-lived engines that I’ve been involved with (hrs and yrs wise), have been engines in commercial or recreational trawler type applications run at 50% of rated HP or less. ...

My most effective cruising speed is one knot below hull speed, creating a 40-percent load on the 80 HP JD4045 engine. Maximum speed is at 72-percent load.

 

[Bigsfish]

BandB

I was told by a mechanic that common rail Diesels don't need to be run up to clean them out. Have you ever heard that?

 

[BandB]

BandB

I was told by a mechanic that common rail Diesels don't need to be run up to clean them out. Have you ever heard that?

Yes and no. I've heard that but I've also seen recommendations from the engine builders to do so periodically. Also the engineers I've spoken with believe that varying speeds is beneficial although not essential. I've often based my normal usage somewhat on the break-in recommendations for hours 10 through 50 or whatever the builder has. The issue certainly isn't the same with common rail but I think the occasional run up is still more widely recommended than not.

 

[AusCan]

Most diesel engines have a peak thermal efficiency of somewhere around 30-45%, Almost all of the rest of the energy (55 - 70%) is lost as heat.
The efficiency curve on normally aspirated engines peaks at about 60-70% of their maximum horsepower. This is usually just above the speed the engine is producing peak torque.

That is where I like to run my engine under normal cruise conditions.

The myth about low loads destroying an engine is mainly based on generators. A very low load at a constant speed is not good for an engine. Our boat engines are never run like that, so it's not an issue.

 

[Bigsfish]

BandB

Thanks. My common rail get run up about once a day for about 20 minutes, my old Cats would get run up every two hours. Unfortunately nothing is definitive.

 

[BandB]

BandB

Thanks. My common rail get run up about once a day for about 20 minutes, my old Cats would get run up every two hours. Unfortunately nothing is definitive.

Common rail drastically reduced issues of low speed operation even for performance engines.

 

[dhays]

BandB



Thanks. My common rail get run up about once a day for about 20 minutes, my old Cats would get run up every two hours. Unfortunately nothing is definitive.

Despite Cummins not recommending it, I've heard from a LOT of experienced mechanics to do exactly what you describe for the common rail electronic engines. Now, do those experienced mechanics recommend it because it is "conventional wisdom" or do they have actual experience with engines that have had problems with carboned up injectors on engines where this hasn't been done? I don't know.

On my last engine, after running it at 1400 for 250 hours over the course of the year I owned it, the injectors looked dirty with carbon build-up on inspection. Don't know if it was the way it was operated or not. I know that since then I have changed my practice. I know do as you do, 20 minutes at 1800 rpm after a day of slow running.

 

[markpierce]

Gee, it takes about 20 minutes to reach operating temperature under load here. Prefer to operate at least three and more hours at a time, but hopefully at least 40 minutes from a cold engine.

 

[O C Diver]

Goes twice as fast with the JD.

No longer a semi planing boat, displacement speed only.

Ted

Ted

You'll have to explain to me over beers how a lower hp can get more speed. I don't doubt a thing you say but that sounds strange.

I was kidding you. Boat use to cruise 14 knots at 1.5 GPM. It now cruises at 7 knots at 3.5 MPG.

Ted

 

[Bigsfish]

Dave

Thanks. I think I'll keep following that regime.

 

[Bigsfish]

Ted

That makes sense. Your word is gospel and I would never tell you that your a fusking liar but I was thinking it. LMAO
Tonight I'll sleep better.

Thanks.

 

[BandB]

Despite Cummins not recommending it, I've heard from a LOT of experienced mechanics to do exactly what you describe for the common rail electronic engines. Now, do those experienced mechanics recommend it because it is "conventional wisdom" or do they have actual experience with engines that have had problems with carboned up injectors on engines where this hasn't been done? I don't know.

On my last engine, after running it at 1400 for 250 hours over the course of the year I owned it, the injectors looked dirty with carbon build-up on inspection. Don't know if it was the way it was operated or not. I know that since then I have changed my practice. I know do as you do, 20 minutes at 1800 rpm after a day of slow running.

I don't think it's necessarily "conventional wisdom", more a holdover from days prior to common rail. However, I do still believe that on engines designed to have more power, it's wise to occasionally running up to cruise is a wise safeguard, perhaps beneficial, definitely not harmful.

We're dealing on this site with new and old but also with small engines where they are already run at a "full cruise" speed vs larger engines that are run the majority of the time by some at very low loads.

One other comment along these lines. Many are hesitant to ever run at WOT. Yet, part of routine maintenance in most guides is to run it at WOT to see the RPM being reached and determine if it's performing correctly. It only takes a couple of minutes. Tracking RPM at WOT is helpful in fully evaluating the health of the engine.

 

[dhays]

One other comment along these lines. Many are hesitant to ever run at WOT. Yet, part of routine maintenance in most guides is to run it at WOT to see the RPM being reached and determine if it's performing correctly. It only takes a couple of minutes. Tracking RPM at WOT is helpful in fully evaluating the health of the engine.

True. I don't like running at WOT. On my boat it is just uncomfortable. Even with the trim tabs, I just dig a big hole in the water and it is very loud. Did it at the sea trial and probably should do it yearly in the early spring to check all systems.

 

[BandB]

True. I don't like running at WOT. On my boat it is just uncomfortable. Even with the trim tabs, I just dig a big hole in the water and it is very loud. Did it at the sea trial and probably should do it yearly in the early spring to check all systems.

We don't run much at WOT either as a lot of running WOT wouldn't be good for the engines we have. Not like a continuous duty reduced hp engine. We love the speed and feel of WOT. We seldom run it and never exceed five minutes doing so.

 

[Humancell]

That's all based on every weekend of the year and 16 hours per weekend. Doing weekend cruising you're definitely not going to average 8 hours a day as you'll be doing other things, not always moving. Then where are you doing 52 weeks a year?

Looking ahead think of the Loop. You can go 6000 miles or 8000. Let's go with 6000 nm. If you're getting 2 nmpg, that's 3000 gallons or 3 nmpg that's 2000 gallons. At $3 per gallon, it's $9000 or $6000.

Now, let's look at a Beneteau Swift Trawler as a representative of semi-planing. At 7 knots, you get 2.1 nmpg, at 10 knots you get 0.7 nmpg, at anything from 12 to 21.3 knots, you get 0.5 nmpg. On the performance curve for that boat you see huge differences. So you could do 6000 nm with only 2857 gallons but if you decided to spend half your time at 10 knots you'd use 4285 gallons. And, if you decided 1/3 of your time at 7 knots, 1/3 at 10 knots and 1/3 at 15 knots, now you're more like 5485 gallons. So, obviously on this boat you can impact your fuel cost by as much as $7,884. Suddenly the insignificant fuel cost may not be as insignificant.

Yes ... as I have been doing research so far (and of course far from complete!) I've seen people averaging 50 miles a day, and driving a boat 2.5-3 days a week to do the loop in a season. I'm completely open to being wrong about that ...

My choice of the "weekends" was really just a starting point for conversation and the 16 hours was based on the low end of driving two days a week to explore the loop. My work can be done from anywhere with power and Internet, and so my plan is to drive the loop, working from wherever I am, and moving the boat 2-3 days a week. I then plan to spend the other 4 wherever I am anchored or moored. Also ... most of all ... I'm learning from people such as yourself so that I might end up modifying my plans ...

I am in full agreement with you on your fuel consumption examples ... and these are the exact issues that I'm working into my plan. When I cruised the Puget Sound, and also when cruising in Alaska, I learned to enjoy a nice slow pace to be economical with fuel. If I'm about to spend 2-3 years cruising the Loop and the Mississippi tributaries I do not want to be in a rush, and plan to cruise at a nice, slow, economical pace.

 

[Humancell]

I'd add that what nobody talks about is what the number for the ST would be at 6 knots. If it's 2.1 @7.0 I'd wager it's > 3.0 nmpg @6.0. Maybe that's outside design specs for that particular boat, but there are huge economies in traveling at no wake speeds. But few are patient enough to do it.

I really appreciate this post - and several others - where I'm realizing that beyond the fuel economy the other key design specs are related to the recommended engine RPM.

So now it's really balancing fuel consumption with speed and time ... and ensuring that the engines are running long term within the proper/recommended RPM range.

 

[Humancell]

Here is the story of my last 12 months with 3,500 nm, in three parts.

Part 1 was 1,000 nm north from Brisbane to half way up the Great Barrier Reef. I was impatient, and had the 'throttle' levers pushed forward a fair way....

Part 2 is the 1,000 nm return. Mostly, er...what is the rush? But with some pushing on long days to cover as much distance as possible when winds were favourable.

Part 3 is 1,500 nm mostly in SE Queensland, mainly in Moreton Bay. Ebb and flood tides can influence speed by +/- 1.4 kn, and more often than not I 'ride the tide' so speeds vary from about 6.7 kn to 9.5 kn when operating at 1600 rpm, 10 litres per hour per engine.

Next year I plan on taking 5-6 months and going further north than last years trip. If the total trip is 4,000 nm then slowing down a bit -target 8 kn cruise - will be very much worthwhile in terms of fuel cost/efficiency.

Fascinating chart ... what does "Frequency" represent?

 

[Humancell]

My boat came with analog fuel flow meters, they are extremely accurate. I call them "throttles".

Oh wow ... the Bayliner 3870 came with the meters? I'm creating a short list of potential boats for my first Loop experiments, and the 3870 and 3870 MY are on that list.

Where all have you taken her? And what kinds of nmpg and gph are you getting at what speeds?

 

[Nomad Willy]

I have looked through the original Cummins manuals that I have. They talk a lot about how to get maximum life and performance out of the Cummins QSB380 HO engine. The manuals discuss not running the engine at idle for extended periods of time at temperatures before normal operating temps. They do recommend idling the engine for 3-5 minutes before gradually increase rpm and load. They are issue very strong warnings about operating the engine at max throttle for an extended period of time. Nowhere in the manual to they recommend or warn against running the engine at a low power setting.

In fact, one of the options that was available (not sure it is available now as it seems like a silly idea) was a "Marine Cruise Control". This was an electronic control that had two, preset rpms for "Cruise 1 and Cruise 2". The factory preset for Cruise 2 was 1200 rpm. In this engine, 1400 rpm is about 25% load. 1200 would be significantly less. Cummins seems to believe that operating this engine at a very low power setting is just fine.

So, while Tony Athens may be opinionated, a bit abrasive, and derisively dismissive of engineers, he is also an extremely experienced Cummins mechanic. He has no problems calling out what he sees as bad ideas on the part of Cummins, but in this case he and the engineers seem to agree.




A while back there was a Bayliner 4788 available for sale in BC. If I recall it was repowered with two low-power Yanmar engines. I remember thinking that for my purposes, that would be a nice combination. I also recall seeing a Great Harbor 37 that was powered with Yanmar 4jh4 56hp engines (same great engine that is in my sailboat).

Turns out the Bayliner was repowered (and had a completely new electrical system as well as new carpeting, cushions etc) because it had sunk at the dock one winter.

Dave,
OK engines should probably have a little of everything kinda like a truck. But trucks work crazy hard on mountian passes even at high noon in the desert. And after 10 years of condemning light loading of trawler engines I give up. Won't mention it again unless I am asked something or forget. That may be hard for me as there's few things on TF that interest me these days. Spend much more time reading about world affairs, politics and even FB. But I'll try.

So Tony A is dismissive of engineers is he? HaHa I'll bet he dosn't like the fact that about many things engine they know a lot more about engines than he does. Grinding valves, replacing a starter motor, exhaust manifold ect ect or working on a fuel injection system his knowledge, experience and skills are tops. I'm assuming he's a mechanic. That's his domain. But specifying how an engine is to be installed in equipment and operated ... that's the domain of an engineer. And almost certianly specifying how much power should be installed in a given application will require more than one engineer. And until wrenching the installation or maintenance is required no mechanics need apply.

And I'm not putting down mechanics. Trying to put them in their place though. They are benders of wrenches and fixers. They should leave engineering to engineers.

 

[BandB]

Dave,
OK engines should probably have a little of everything kinda like a truck. But trucks work crazy hard on mountian passes even at high noon in the desert. And after 10 years of condemning light loading of trawler engines I give up. Won't mention it again unless I am asked something or forget. That may be hard for me as there's few things on TF that interest me these days. Spend much more time reading about world affairs, politics and even FB. But I'll try.

So Tony A is dismissive of engineers is he? HaHa I'll bet he dosn't like the fact that about many things engine they know a lot more about engines than he does. Grinding valves, replacing a starter motor, exhaust manifold ect ect or working on a fuel injection system his knowledge, experience and skills are tops. I'm assuming he's a mechanic. That's his domain. But specifying how an engine is to be installed in equipment and operated ... that's the domain of an engineer. And almost certianly specifying how much power should be installed in a given application will require more than one engineer. And until wrenching the installation or maintenance is required no mechanics need apply.

And I'm not putting down mechanics. Trying to put them in their place though. They are benders of wrenches and fixers. They should leave engineering to engineers.

You basically put down anyone who disagrees with your position and in this case it's mechanics and Tony Athens and also Dave and owner's manuals.

The issue Dave was addressing here isn't what engine the builder should put in a boat, it's the use of the engine already in. There is no engine manufacturer of common rail engines issuing warnings against running their engines at low loads. So, you disagree with that. Accept that but don't diminish the knowledge of others.

Tony Athens has established himself in a narrow area of the industry and in that area is well respected. I don't always agree with him, but I'm not going to disrespect him and call him nothing more than a bender of wrenches and fixers. Clearly you know nothing about his experience. Now, it's fine to have opinions different than his, but you don't have to be insulting to express them.

 

[Nomad Willy]

As for whether or not an oversized engine or a minimal power engine is best for economy .. that's easy. At least if one knows how much power is required and does some research into power per fuel burn .. excluding dock talk and the like. All or most modern engines and many to most engines 40 or so years old are very well documented as to how much fuel is burned to produce X amount of power at any or most any load and rpm.

Trawler skippers (generally speaking) like big, heavy and slow engines. They got here liking big, heavy and slow trawlers. So they are naturally disposed to that and distain small, light and high speed engines. No wonder many want to slog about going slowly w big heavy trawlers and engines. And to do it because it sounds big and heavy. Never mind that there are elements of this that a really objective person or an engineer would put in the thumbs down category.

 

[dhays]

And I'm not putting down mechanics. Trying to put them in their place though. They are benders of wrenches and fixers. They should leave engineering to engineers.

I think the problem comes when, at times, an idea that looks good on paper doesn't perform as well out in the real world. A mechanic is the one that is stuck fixing problems that seem to be avoidable with better design choices.

I would imagine that any type of engine design is an entire set of compromises. A mechanic could see what is an obvious design problem, but then they weren't there when all of the other options were being considered. The mechanic just comes up with a fix for the application they are working with at the time. However, I know nothing about engines and even less about engineering, so I have no opinion either way.

 

[Insequent]

Fascinating chart ... what does "Frequency" represent?

Is just 3 histograms in one chart, but with lines instead of bars, which I think made it easier to read.

 

[FF]

"The factory preset for Cruise 2 was 1200 rpm. In this engine, 1400 rpm is about 25% load. 1200 would be significantly less."

What is overlooked is that what percentage of WOT power used is not important.

It is the percentage of power available AT the operating RPM that counts.

If the engine is modestly loaded at 1200RPM (as many 60 CPS prime noisemakers are )

or 1500 for the 50 CPS folks , the engine runs a long time with little hassle because it is properly loaded

That it might be 30% of WOT Flank max RPM power is meaningless.