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Old 03-03-2013, 05:31 PM   #41
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Did you know that a squirrel or chipmunk collects and hides roughly 12 years worth of food each year of their life as a habit and obviously never finds or eats most of it.
I knew that! I always thought, however, that it is part of Nature's reforestation program.
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Old 03-03-2013, 05:54 PM   #42
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Greetings,
Well, I see how the squirrel information could quickly relegate this thread to OTDE....tread carefully.
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Old 03-04-2013, 08:51 AM   #43
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Higher top speed means better glossy brochures, magazine articles, etc

Great , the problem is except for cigarettes and some sport fish few owners operate at "top speed".

Then the boat requires a very different view of what is optimum or efficient.

Anyone operate on the pin these days?
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Old 03-04-2013, 10:21 AM   #44
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Marketing determines the engine size...

Models with 2 or more different engine sizes will most likely determine what option sizes will be offered in the next model year....Straight from the regional director of marketing for Sea Ray a few years back.

He also explained why a million dollar boat will use a plastic hinge on an access panel in the engine room and not in the galley of many of those expensive boats....
I think expecations pf potential trawler buyers and potential Sea Ray buyers are worlds apart. That Sea Ray needs a lot of power to get up on plane and folks expect Sea Rays and similar boats to go fast.

When one decides a trawler is best suted for his/her needs, the decision has already been made that not being able to go fast is not an issue.
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Old 03-04-2013, 10:38 AM   #45
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Anyone operate on the pin these days?
Probably 90% of the recreational boats sold. I sure maxed out RPM a lot with the multitude of sunny day lake type water toys I've owned over the years - especially heavy ski boats with 6 - 8 people onboard.
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Old 03-04-2013, 11:16 AM   #46
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I'm suprised everyone missed this...

I would argue that underloading with a modern diesel isn't happening at all!

Won't argue wether its bad or not, I just do not think its happening.

Here's why... Lets take the Cummins 5.9L engine as our for example.

That engine is available from Cummins in HP ratings of everything from 220 to 370HP.

The differences between the engines are all add on components. Stuff like turbos, aftercoolers, and MAX RPM ratings.

None of this has anything to do with the basic block, pistons, etc... that are the components involved in "wet stacking".

If my 47' boat had 220 HP cummins engines I do not believe it would be over powered enough to have engine problems.

Now, add on all the stuff that makes the engines capable of producing 370 HP, but run the boat at the same speed as you did with the 220HP engines and you have the exact same cylinder pressures as you had with the smaller engines. Remember at low RPMs the turbos are not producing boost, etc... everything is the same.

I think thats why we don't see underloading related engine failures in modern marine diesels.
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Old 03-04-2013, 11:49 AM   #47
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I'm suprised everyone missed this...
I think thats why we don't see underloading related engine failures in modern marine diesels.
I didn't, see post #23 and #36. A month ago I had a discussion with Cat and Cummins guys on this exact issue. They are "largely" in your camp, or better stated you in theirs.
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Old 03-04-2013, 12:04 PM   #48
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I didn't, see post #23 and #36. A month ago I had a discussion with Cat and Cummins guys on this exact issue. They are "largely" in your camp, or better stated you in theirs.

Sorry Sunchaser for missing your posts.

It seems at least on this subject we are thinking alike. I feel a little smarter (or luckier) now that you confirmed this line of reasoning with some factory trained techs.
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Old 03-04-2013, 12:48 PM   #49
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I think thats why we don't see underloading related engine failures in modern marine diesels.
I sure am not going to pretend that I am well versed in the technical workings of the modern diesel engine. I do believe that the "under loading problem", so prevalent on this forum, is really overblown. ksanders and Sunchaser's posts make total sense to me. Having a tiny little engine that allows one to achieve hull speed is just one part of the equation. Having more hp for hanging some extra stuff on the engine and the ability to achieve more speed (even at the expense of doubling the fuel flow) in certain instances, makes even more sense to me. At trawler speeds, even the big engines are pretty economical.
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Old 03-05-2013, 06:32 AM   #50
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Now, add on all the stuff that makes the engines capable of producing 370 HP, but run the boat at the same speed as you did with the 220HP engines and you have the exact same cylinder pressures as you had with the smaller engines. Remember at low RPMs the turbos are not producing boost, etc... everything is the same.

"everything is the same."

Perhaps but many MFG will have slightly different internal builds .

The Turbo engines frequently have trapizoidial rings , rather than square cut , which do suffer from under loading.

So running a 200hp rated engine at 100hp may be OK , but its brother built to 380 hp specks may suffer .
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Old 03-05-2013, 01:34 PM   #51
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Mechanically put what is the under loading issue? I can think of only two.

1. The Tempuratures of the mechanical parts in the engine aren't high enough to keep unwanted solid or gummy deposits from forming around the rings and preventing the rings free enough movement to ride up and down the cylinder in full contact w the cylinder wall controlling oiling and gas sealing duties per/re the design of the ring.

2. Insufficient combustion pressure to exert on rings like "Keystone" style rings the needed pressure to force the ring to exert enough pressure on the cylinder walls to prevent glazing of the cylinder walls that would reduce the ability of the rings and cylinder walls to seal gasses and allow the engine to perform normally.

A bit wordy and I'm sure many could do better but my point is probably made. If wer'e going to discuss this, much too much argumentative water has gone under the bridge without identifying the actual problem ... Or perceived problem.

#1 and #2 above is very basically the problem as I see it. What more is ther'e really to it? Does the sideways pressure of the piston against the cylinder wall get into the picture or perhaps it's the driving force re glazing?

Want other ideas/opinions.
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Old 03-05-2013, 02:04 PM   #52
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Engine temperatures are easily dealt with, a thermostat maintains the jacket water temperature and reducing the flow rate or bypassing part of the raw water flow will keep lube oil temps up if you have a seawater cooled oil cooler.

The cylinder pressure difference between 50% load and full load is not all that great.

A turbocharged engine may suffer overheating of valves from extended periods of low loading (<50%) due to reduced charging pressure and the cooling produced by valve overlap.

All the rest is mythology and dock talk.
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Old 03-05-2013, 05:45 PM   #53
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"A turbocharged engine may suffer overheating of valves from extended periods of low loading (<50%) due to reduced charging pressure and the cooling produced by valve overlap."



Rick, is this in reference to maximum output at crankshaft?

Thanks. SteveH
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Old 03-05-2013, 06:06 PM   #54
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I'm surprised Rick. I thought coolant temperature had little to do w lube oil temp, piston or valve temps. I thought it was the low temps of piston and ring temps that drove this under loading issue. I see "if you have a seawater cooled oil cooler." ... I would think the oil cooler would be counter productive to benefit an underloaded engine. In fact if I were to constantly under load an engine I'd consider removing or blocking the oil cooler.

Rick says "A turbocharged engine may suffer overheating of valves from extended periods of low loading (<50%)" Well that includes just about everybody on this forum that has a turbocharged engine.
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Old 03-05-2013, 07:44 PM   #55
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"A turbocharged engine may suffer overheating of valves from extended periods of low loading (<50%) due to reduced charging pressure and the cooling produced by valve overlap."



Rick, is this in reference to maximum output at crankshaft?

Thanks. SteveH
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Old 03-05-2013, 08:05 PM   #56
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I'm surprised Rick. I thought coolant temperature had little to do w lube oil temp, piston or valve temps.
If the oil cooler is cooled by jacket water then it stays at the correct temperature as long as the thermostat works.

If the oil is cooled by seawater then it might overcool.

Coolant temperature has a great deal to do with piston and valve temperatures ... all the things that go sideways when the raw water impeller fails or the freshwater goes away ... it is the dreaded "overheating."

Valves are cooled by jacket water passages in the head and by charge air during valve overlap. A turbocharger with a worn compressor can lead to valve failure.

Larger engines use staged turbochargers so that charge air flow matches the load more closely. Very large engines with multiple turbos are now being fitted with kits to block off all but one so the engine can operate for extended periods at outputs as low as 10 percent.




Quote:
I thought it was the low temps of piston and ring temps that drove this under loading issue.
Underloading problems are a combination of high piston speeds with low loading as occurs in generator engines. It is not such a big deal with propulsion engines except when the power output is very low for long periods since low loads are not experienced at high piston speeds.


Quote:
I see "if you have a seawater cooled oil cooler." ... I would think the oil cooler would be counter productive to benefit an underloaded engine. In fact if I were to constantly under load an engine I'd consider removing or blocking the oil cooler.
It depends on how the oil is cooled, I wouldn't remove it, I would restrict coolant flow or bypass it. You need to keep the oil hot enough to maintain the correct viscosity so it lubes everything and doesn't waste a bunch of power to just pump it around. A jacket water cooled oil cooler keeps the oil hot ... or should.

Quote:
Rick says "A turbocharged engine may suffer overheating of valves from extended periods of low loading (<50%)" Well that includes just about everybody on this forum that has a turbocharged engine.
Maybe 50 percent was a bad choice of power level, maybe I should have written 25 percent. You make a good point though since we are not bombarded with posts by owners of turbocharged boats telling us about how their engines were wrecked by underloading. so that alone speaks to the reality of this perceived underloading "problem."
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Old 03-05-2013, 10:15 PM   #57
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VERY informative Rick.

My little Mitsubishi warms up really fast. Three or 4 minutes. Marches right up to 180 to 185 and in five it's 190degrees. Does this at 1100rpm no load. 2300 rpm and heat soaked it's still 190. At 2500 for awhile it climbs just a little as in 3 or 5 degrees. Any idea why my engine is so stable coolant temp wise? Only 2 unusual things. A steel exhaust manifold w lots of extra coolant space and hence coolant because the heat exchanger is not in the manifold. I put it on the aft bulkhead.
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Old 03-05-2013, 10:23 PM   #58
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Greetings,
Mr. m. "Any idea why my engine is so stable...". MY guess: Well designed and efficient cooling passages and a thermostat that works.
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Old 03-05-2013, 11:18 PM   #59
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Could be RT but it almost seem too good to be true. Perhaps it has to do w where they put the coolant temp sensor or the position of the thermostat re the position of or the flow of the water pump or ....................... ?
My engine thanks you for the compliment.
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Old 03-06-2013, 06:42 AM   #60
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Could be RT but it almost seem too good to be true.
I think RT nailed it. The sensor is probably located at the hottest point, your cooler works well and the thermostat is effective. That is about as good as it gets.

If you really want to see what is going on, clag some thermocouples or RTDs on the various coolant inlets and outlets and collect the outputs in a datalogger for a few hours at varying loads.

The first half hour or so after start up will be very enlightening for you. After that things will stabilize and not be very exciting.
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