Nomad Willy
Guru
diver dave,
I don’t get it ........
What’s the point?
I don’t get it ........
What’s the point?
Minimum Cruising RPM
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The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
diver dave
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The point relating to wear requiring metal to metal contact.
The vid show iron, much tougher than babbitt, being cut, a foot at a time, by just fast water, in minutes.
The vid show iron, much tougher than babbitt, being cut, a foot at a time, by just fast water, in minutes.
You won't be cutting iron with water. A water jet cutter works because the water has an abrasive mixed in it, usually ruby garnet for something like steel or iron. The garnet does the cutting. Plain water only works for very soft materials. Leave the abrasive out and you could spray water on that anvil for a year.
So, if you dissolve ruby garnet in your engine oil, and the filter doesn't take it out, you might be in trouble.
So, if you dissolve ruby garnet in your engine oil, and the filter doesn't take it out, you might be in trouble.
RickyD
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I have no clue what this means. "but bugger the engine converter for a BMEP or fuel map and you can be assured of operating in a long life ,efficient band."
What engine converter? Bugger? BMEP?
What engine converter? Bugger? BMEP?
diver dave
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Nomad Willy
Guru
RickyD,
BMEP means “brake mean effective pressure”. A fancy expression for combustion chamber pressure during combustion. I’m not really sure that’s it but hoping to learn what it really is from someone else.
BMEP means “brake mean effective pressure”. A fancy expression for combustion chamber pressure during combustion. I’m not really sure that’s it but hoping to learn what it really is from someone else.
North Baltic sea
Guru
Hi,
This is the thing I asked directly at Cummins US and they replied qsb 5.9 could drive +800 rmp happily without any problem with glazing or carbon. Your rounds are sure to be fine on your engine.
NBs
FF
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"What engine converter? Bugger? BMEP?"
Many boat engines are marinized truck, or industrial engines , just as loads of gensets are yard implement engines with a different gov to allow genset use.
Bmep plotted , or better a Fuel Map is a chart of load /rpm that looks like a cloud or a set of bullseyes .
In the center is the best fuel consumption the engine can do, as the rings get larger the fuel burn is higher.
IF one can operate in the bullseye the boat is at its peak efficiency, the great value to many is seeing how few RPM out of the center the performance is really poor.
"This is the thing I asked directly at Cummins US and they replied qsb 5.9 could drive +800 rmp happily without any problem with glazing or carbon."
This is true IF the engine has a sufficient percentage of permitted load at 800RPM.
If the engine can create say 40 hp at 800RPM , and you operate at 30HP, all should be well.
If you operate at 800rpm , 10 hp , slobbering , cylinder burnishing and excessive blowby probably are happening.
Fuel Consumption Contours
The interesting part of the fuel map is the contours of specific fuel consumption. The units (grams per kilowatt-hour, or grams per horsepower-hour) are normalized such that any two engines using similar fuels can be directly compared, even if the engines are of very different types and sizes. A 40,000 hp ship diesel consuming 150 g/kWh uses half as much fuel, relative to its output power, as a 20 hp motor consuming 300 g/kWh.
Many boat engines are marinized truck, or industrial engines , just as loads of gensets are yard implement engines with a different gov to allow genset use.
Bmep plotted , or better a Fuel Map is a chart of load /rpm that looks like a cloud or a set of bullseyes .
In the center is the best fuel consumption the engine can do, as the rings get larger the fuel burn is higher.
IF one can operate in the bullseye the boat is at its peak efficiency, the great value to many is seeing how few RPM out of the center the performance is really poor.
"This is the thing I asked directly at Cummins US and they replied qsb 5.9 could drive +800 rmp happily without any problem with glazing or carbon."
This is true IF the engine has a sufficient percentage of permitted load at 800RPM.
If the engine can create say 40 hp at 800RPM , and you operate at 30HP, all should be well.
If you operate at 800rpm , 10 hp , slobbering , cylinder burnishing and excessive blowby probably are happening.
Fuel Consumption Contours
The interesting part of the fuel map is the contours of specific fuel consumption. The units (grams per kilowatt-hour, or grams per horsepower-hour) are normalized such that any two engines using similar fuels can be directly compared, even if the engines are of very different types and sizes. A 40,000 hp ship diesel consuming 150 g/kWh uses half as much fuel, relative to its output power, as a 20 hp motor consuming 300 g/kWh.
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Jetstream
Senior Member
We ran our 6BTA370's at 1200 rpm for about 95% of the time for many years after taking Tony Athens advice. That was comfortable for us and very economical at 7 knots. Have a look at the torque chart for the engine. If propped correctly to get 3000 rpm minimum at WOT, 1200 rpm will give you about 100hp. Some of the normally aspirated 6BTA's only make 180hp.
Every now and then we would run for a while at maximum cruise of 2800rpm (200 rpm under book figure WOT as per Cummins recommendation) more for the fun of it or to get to somewhere faster although I do think it helps blow out the cobwebs so to speak. In short it won't hurt your engine at all.
Every now and then we would run for a while at maximum cruise of 2800rpm (200 rpm under book figure WOT as per Cummins recommendation) more for the fun of it or to get to somewhere faster although I do think it helps blow out the cobwebs so to speak. In short it won't hurt your engine at all.
Hard to find the consumption map for a particular engine though. In your example, from 1000 - 2000 rpm at ordinarily achievable prop loads, the consumption looks pretty flat.
I also though max torque was always achieved at 100% load. That is unlikely at 1400 rpm on a small marine diesel, unless you have a variable pitch prop. Looking at the fuel consumption map, it doesn't appear that a variable pitch prop would offer much savings in fuel.
I also though max torque was always achieved at 100% load. That is unlikely at 1400 rpm on a small marine diesel, unless you have a variable pitch prop. Looking at the fuel consumption map, it doesn't appear that a variable pitch prop would offer much savings in fuel.
Nomad Willy
Guru
FF,
Thanks for finally giving us some more info on the fuel map.
What engines that are common to fairly common in trawlers have an acessable fuel map? Or/and how does one find it?
There’s Steve DeAntonio and Tony Athens and probably a half a dozen other “experts” that have comunicated far and wide that have ventured an opinion on the load issue. Then there’s engineers. What you read or hear from manufacturers mostly comes from engineers. That’s why I prefer the opinions from engineers. And of course a sanitation engineer dosn’t measure up for our purposes.
Then there’s common sense. Would you buy a car that had never exceeded 30mph? There’s thrmostats that artificially raise the coolant temp to much much higher that it otherwise be. One should think about why they put them in engines. Ever seen an engine since WWI that lacked the thermostat? Running engines at optimum temps has long been a must do thing.
And there has been much written about engine oil and how hot it should be w the engine working. And of course there are different oils.
Much to consider for a pleasureboat skipper. When I was a young man very seriously sludged up engines were common. My father intrusted me w the job of “fixing” his 6cyl 1960 Chevrolet in about 1964. I ran the car w mostly kerosene and a quart or two of 50w oil. Didn’t save it. Many people switched to the then new detergent oils but very often considerable oil leaking and/or blowby and smoking would result. Theromstats, synthetic oil, detergents, viscosity improvers, ring design and other things have been implimented that help reduce the problems associated w sludging. But sludging is still an issue. Some makes and year models of newer cars are chronically burdened w sludging.
So to dismiss this issue on old diesel trawlers seems a knee jerk reaction.
Thanks for finally giving us some more info on the fuel map.
What engines that are common to fairly common in trawlers have an acessable fuel map? Or/and how does one find it?
There’s Steve DeAntonio and Tony Athens and probably a half a dozen other “experts” that have comunicated far and wide that have ventured an opinion on the load issue. Then there’s engineers. What you read or hear from manufacturers mostly comes from engineers. That’s why I prefer the opinions from engineers. And of course a sanitation engineer dosn’t measure up for our purposes.
Then there’s common sense. Would you buy a car that had never exceeded 30mph? There’s thrmostats that artificially raise the coolant temp to much much higher that it otherwise be. One should think about why they put them in engines. Ever seen an engine since WWI that lacked the thermostat? Running engines at optimum temps has long been a must do thing.
And there has been much written about engine oil and how hot it should be w the engine working. And of course there are different oils.
Much to consider for a pleasureboat skipper. When I was a young man very seriously sludged up engines were common. My father intrusted me w the job of “fixing” his 6cyl 1960 Chevrolet in about 1964. I ran the car w mostly kerosene and a quart or two of 50w oil. Didn’t save it. Many people switched to the then new detergent oils but very often considerable oil leaking and/or blowby and smoking would result. Theromstats, synthetic oil, detergents, viscosity improvers, ring design and other things have been implimented that help reduce the problems associated w sludging. But sludging is still an issue. Some makes and year models of newer cars are chronically burdened w sludging.
So to dismiss this issue on old diesel trawlers seems a knee jerk reaction.
markpierce
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From the engine performance chart JD once had at its website.
Nomad Willy
Guru
Mark,
How do you (or do you) know/think the 1400rpm torque is at what your boat sees while underway or what the engine produces at WOT at 1400rpm on the dyno?
How do you (or do you) know/think the 1400rpm torque is at what your boat sees while underway or what the engine produces at WOT at 1400rpm on the dyno?
markpierce
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Eric: based on JD chart. I don't have boat-specific info other than fuel consumption, RPM, and speed. Also, my understanding is that max torque is achieved at less than WOT.
I can't claim a perfect understanding, but here's what I think happens:
The engine torque curve goes up and right and flattens. The prop absorption curve goes right and bends up. On a diesel there is no "throttle", rather there is a lever that sets the rpm governor set point. In turn, the rpm governor controls the fuel rack, and will attempt to add or pull fueling so that the governor commanded rpm is met. On a more modern common rail diesel this is all done electronically rather than mechanically, but works the same otherwise.
When you set 1400 rpm on the "throttle" - really the rpm governor - if there is enough torque in the engine to reach that speed it will add fuel until it does. If there is not enough torque, it will not reach that rpm and will be effectively overfueled, smoking. If there is more than enough torque, it will reach that rpm and the fuel rack will be pulled back by the governor, maintaining the rpm at a lower torque than maximum available.
A properly sized and pitched prop can only absorb the maximum torque the engine can produce at one point: maximum rated rpm, where the two curves meet. Anything less than that there is excess torque available, the rack will be pulled back, and the engine will be operating at less than full torque load. This difference is shown as the vertical space between the engine and prop torque curves supplied by the manufacturer.
So while maximum torque can be achieved by the diesel at less than WOT (in your case at 1400 rpm), it will not be operating that way on a boat. On a tractor let's say, you could set the "throttle" for 1400 rpm, then load the engine. As you increase the load, fuel will be added by the governor to maintain speed. When the load reaches the maximum torque the engine can produce, the governor and fuel rack can do no more, and the engine will slow down and begin to labor and smoke.
Common rail engines can recognize this condition and protect themselves from overfueling, but a mechanically governed engine isn't that smart.
The engine torque curve goes up and right and flattens. The prop absorption curve goes right and bends up. On a diesel there is no "throttle", rather there is a lever that sets the rpm governor set point. In turn, the rpm governor controls the fuel rack, and will attempt to add or pull fueling so that the governor commanded rpm is met. On a more modern common rail diesel this is all done electronically rather than mechanically, but works the same otherwise.
When you set 1400 rpm on the "throttle" - really the rpm governor - if there is enough torque in the engine to reach that speed it will add fuel until it does. If there is not enough torque, it will not reach that rpm and will be effectively overfueled, smoking. If there is more than enough torque, it will reach that rpm and the fuel rack will be pulled back by the governor, maintaining the rpm at a lower torque than maximum available.
A properly sized and pitched prop can only absorb the maximum torque the engine can produce at one point: maximum rated rpm, where the two curves meet. Anything less than that there is excess torque available, the rack will be pulled back, and the engine will be operating at less than full torque load. This difference is shown as the vertical space between the engine and prop torque curves supplied by the manufacturer.
So while maximum torque can be achieved by the diesel at less than WOT (in your case at 1400 rpm), it will not be operating that way on a boat. On a tractor let's say, you could set the "throttle" for 1400 rpm, then load the engine. As you increase the load, fuel will be added by the governor to maintain speed. When the load reaches the maximum torque the engine can produce, the governor and fuel rack can do no more, and the engine will slow down and begin to labor and smoke.
Common rail engines can recognize this condition and protect themselves from overfueling, but a mechanically governed engine isn't that smart.
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