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Old 02-24-2017, 07:59 AM   #21
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I would suggest looking at the complete HP charts for the engine you chose.

Most MFG will wax about their high HP , but its for towing water skiers a few hours a day.

When you get to the 24/7 rating , you will get an idea of what HP the engine should be propped for .

You may find a HUGE difference in ratings ,using the lower 24/7 number should ease your worries about under loading and eventual slobbering.

AS long as there is positive boost pressure a turbo at low loads is ok.
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Old 02-24-2017, 08:46 AM   #22
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When it pertains to anything diesel I Iisten to two experts... Steve D'Antonio and Robert Senter a.k.a. Lugger Bob.

Here is what Steve says about chronic under loading:

The Perils of Chronic Under-Loading | Steve D'Antonio Marine Consulting


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Old 02-24-2017, 08:52 AM   #23
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I've heard it both ways. I've also heard about modern engines vs. legacy engines with no definition of either.


Assuming that you are shopping for an engine because you have a boat that needs an engine replaced, I suggest forgetting about theory and replacing your old engine with an identical engine. That would be a "drop in place" repair rather than new mounts, new instruments, etc.
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Old 02-24-2017, 09:03 AM   #24
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When it pertains to anything diesel I Iisten to two experts... Steve D'Antonio and Robert Senter a.k.a. Lugger Bob.

Here is what Steve says about chronic under loading:

The Perils of Chronic Under-Loading | Steve D'Antonio Marine Consulting


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As Steve D has said for years and repeats in this article, keep that oil temperature up and the "perils" of under loading are kept at bay. And Nomad Willy says same. Makes sense to me.
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Old 02-24-2017, 11:09 AM   #25
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Wifey B: I have a better cure for the issue of underloading. I go faster.
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Old 02-24-2017, 11:13 AM   #26
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Wifey B: I have a better cure for the issue of underloading. I go faster.
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Old 02-24-2017, 02:23 PM   #27
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When it pertains to anything diesel I Iisten to two experts... Steve D'Antonio and Robert Senter a.k.a. Lugger Bob.

Here is what Steve says about chronic under loading:

The Perils of Chronic Under-Loading | Steve D'Antonio Marine Consulting


.
When I see that quote about needing to run at 75% power for best life, he loses credibility. That is nonsense.
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Old 02-24-2017, 02:54 PM   #28
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When I see that quote about needing to run at 75% power for best life, he loses credibility. That is nonsense.
He lost credibility with me long ago, but that's the problem when you claim to be THE expert. I'm not a follower. My engineers don't agree with him on many things.

It's like Pascoe. Just because one has put their opinions on the internet and has the experience to form opinions, doesn't mean they're always right or ones many owners would agree with.

On the 75% issue, on most planing or semi-planing boats, it's typically a good cruising speed and not unhealthy, and we run often between 70 and 80% load, to get places faster, but I don't for one minute think that's healthier than 40-60% load. But that's just personal opinion.
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Old 02-24-2017, 09:28 PM   #29
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Eric

A well designed marine engine has a coolant cooled lube oil heat exchanger. The oil will then remain about 10 degrees above engine temperatures. In my case this is true even at very low loads of about 25%. Once warmed up I can cruise for hours at low loads with engine temperatures remaining in the thermostat controlled operating range of 172 to 180F.
This caught my eye and I'm going back to it as I've never been clear on this heat exchanger or others similar.
"engine temperatures" = coolant? EGT?
Must be coolant as you mention the thermostat.
Under what conditions does the oil "remain about 10 degrees above engine temperatures" ?

I thought the heat exchanger you are talking about was/is called the oil cooler. Seems you're calling it an oil heater. Perhaps the "exchanger" cools the oil at heavy loads and heats it at low loads. That would be rather ideal. But diesels do'nt make much heat at low loads. I've heard you can't even fry an egg on an air cooled truck exhaust manifold at an idle. So I think something needs rearranging in my head.

My engine isn't a "well designed engine" as it only has a oil cooler/heater connected to the transmission. Engine coolant on one side and trans oil on the other. Perhaps you have an idea about what's cooling what on my engine. If it's a cooler where's the heat comming from? If my trans is not slipping heat would only be comming from combustion and that's quite removed from the trans oil.


How much of my notions about "coolers" can you set straight? And I'm most interested in the "well designed marine engine" having an exchanger between the engine coolant and the engine lube oil.
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Old 02-24-2017, 09:55 PM   #30
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I thought the heat exchanger you are talking about was/is called the oil cooler. Seems you're calling it an oil heater. Perhaps the "exchanger" cools the oil at heavy loads and heats it at low loads. That would be rather ideal. But diesels do'nt make much heat at low loads. .
Eric, you have it figured out. Heat and cool oil via coolant with a plate heat exchanger that is mounted on side of engine. The oil always seems to be at least 10F degrees hotter than coolant at low loads and about 15 to 20F at higher loads.

At my low (1500 RPM) to normal (1750 RPM) cruising loads I don't find (measured with IR gun) oil temperatures below 185F once engines have warmed up.
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Old 02-24-2017, 09:59 PM   #31
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Smaller engines give the mechanic more room in the engine room/compartment.
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Old 02-25-2017, 07:18 AM   #32
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From what I read in National Fisherman slobbering is caused by very low loads causing the piston rings to burnish the cylinder walls.

With no pressure behind the rings to seal properly the rings just slide and polish, instead of scrape.

More frequent oil changes will get rid of the acids caused by the blowby , but only a hone or new cylinders can fix the eventual lack of compression.

This is one of the main reasons noisemakers are of two different sizes on larger boats.

The night load is minor , and would be very hard on the day unit.

This is done even tho 2 identical noisemakers would offer easier servicing and a source of spare parts .
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Old 02-25-2017, 11:05 AM   #33
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This is one of the main reasons noisemakers are of two different sizes on larger boats.

The night load is minor , and would be very hard on the day unit.

This is done even tho 2 identical noisemakers would offer easier servicing and a source of spare parts .
Actually, from what I've seen, been around, or owned, generators seem to be of two different sizes a lot on medium sized boats, 60-80', and the larger generator is used regularly while the smaller one never gets used. I've seen many that would have perhaps a 30 kw and a 7 kw and the 30 would have 1200 hours and the 7 would have 150 hours. So, that is being rethought. Other builders like Hatteras have always gone with two identical. Most 80' Hatteras come with two 27.5 kw or so. Now, above 80' they're almost always identical. A 130' boat would typically have two 92 kw or so. On our 65' Sunseeker, the standard is a single 21.5 kw Onan. We wanted a backup and a 7.5 or so was suggested but we went with identical and haven't regretted it.

I've been in a lot of discussion on sizing of the 2nd generator. Theorists and brokers have often said much smaller. Captains and owners with practical experience have gone the other way. Here's why. Let's take the 80' Hatteras above. A 7.5 or 10 kw generator would be virtually useless. First it would mean not running heat or a/c. Most boats in that range will have them set to come on automatically. But then even without them the chances of overloading would be great. Someone showers, someone else decides to whip up breakfast, another goes to the coffeemaker and lights on all around and a 7.5 wouldn't handle it. Just all the refrigeration is going to load one significantly. We have in the galley a refrigerator over two freezer drawers. On the bridge an icemaker and small refrigerator and in the lazarette, two freezer drawers. Even if one or a 10 kw did, they would always be running at 75-95% load, far worse than any possible underloading. On our 65' Sunseeker, we very seldom ever run at less than 35-40% load which means anything under 12 kw or so would be useless and means 21.5 kw isn't underloaded. Instead, by having two identical, we can share parts and spares, split the usage, always have a backup and put fewer hours on. The night load always includes heat or a/c coming on and off over the course of the night. Even if they weren't absolutely needed for temperature control, they are to maintain air movement and to reduce moisture.

Heating, cooling, showering, cooking, lights on a boat above a certain size are typically used exactly the same way you'd use them in a house. On a larger boat, such as 130' with two 99 kw generators, you will always have enough to keep one generator in a satisfactory load range as you'll never require less than 30-40 kw and not often under 50 kw.

While I do agree that traditionally many mid range trawlers have had one large and one small, that is no longer as common and definitely not common on larger boats. Refrigeration and a/c or heat are the driving forces, but there's a lot of other electricity usage. On an 80', late at night, 8 guests, 2 crew members, you may have 6 or more people showering, using hot water, 4 televisions on, 3 freezers, 1 large and 1 small refrigerator, several phones and tablets charging and then the a/c switching on and off, different units at different times.

I've looked at and calculated on many cruising boats 60' and up and just haven't found the large and small combination to make sense. Then observation has shown on boats with a large and small, the small doesn't get used. Most boats in the 60-70' range still run with just a single generator.
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Old 02-25-2017, 12:03 PM   #34
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Eric, you have it figured out. Heat and cool oil via coolant with a plate heat exchanger that is mounted on side of engine. The oil always seems to be at least 10F degrees hotter than coolant at low loads and about 15 to 20F at higher loads.

At my low (1500 RPM) to normal (1750 RPM) cruising loads I don't find (measured with IR gun) oil temperatures below 185F once engines have warmed up.
Sunchaser,
This makes no sense to me at all. The coolant is artificially kept higher than it would normally be by the thermostat. The oil has no thermostat and most of the time it sits in the bottom of the sheet metal oil pan w large area exposed to ambient cool air. I don't think I do "get it".
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Old 02-25-2017, 01:33 PM   #35
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Sunchaser,
This makes no sense to me at all. The coolant is artificially kept higher than it would normally be by the thermostat. The oil has no thermostat and most of the time it sits in the bottom of the sheet metal oil pan w large area exposed to ambient cool air. I don't think I do "get it".
The temperatures I gave are measured with an IR gun on the oil pan. The plate exchanger was sized by the engine manufacturer to provide adequate oil cooling at full load. Next time I'm on vessel I'll send you some pictures of what is happening.

The first time I saw a plate exchanger for cooling diesel engine oil was about 50 years ago on a Cat loader. Plate exchangers for heating and cooling are used in all sorts of industrial applications going back over a century.
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Old 02-25-2017, 01:38 PM   #36
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Sunchaser,
This makes no sense to me at all. The coolant is artificially kept higher than it would normally be by the thermostat. The oil has no thermostat and most of the time it sits in the bottom of the sheet metal oil pan w large area exposed to ambient cool air. I don't think I do "get it".
At low loads, the oil is heated by the coolant loop. At high loads, it is cooled by the coolant loop. The coolant loop simply moderates the oil temp. ANd the coolant loop is large enough to extract the heat out of the oil system. The coolant is also moderated by the thermostat and allows coolant to heat up in low power situations. Does that help?
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Old 02-25-2017, 02:30 PM   #37
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Different folks, different strokes...same for some engines....

Here is what my go to engineer says about all of this...

"The article referenced in post #19: Why You Shouldn't Go Easy on a Diesel - Professional BoatBuilder Magazine, supports those who questioned SD's credibility. I have always said the man is .....(not on the money... see note)

The "turbine wheel" shown is a compressor wheel. It is probably fouled by a crankcase ventilation system that vents to the air filter.

The later article mentioned in post #22 is a different version of the same article but shows a turbine wheel. However, there are several reasons that wheel can be sooted and wet, a leaking seal in the turbo itself is likely. That turbo could have been (and probably was) mounted on a generator. All of the conditions illustrated are more common to generators than propulsion engines. The generators which tend to have that sort of problem use the same engines that are used in smaller boats for propulsion. That makes it easy for someone with more experience selling technical articles to content hungry magazines to commercialize the kind of mythology perpetuated on internet boating forums.

It is more fear mongering for food than practical guidance."

Note....I cut a tidbit that wasn't technical.......well it was but I cut it for a different reason...
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Old 02-25-2017, 06:38 PM   #38
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A couple thoughts:

2 pole generators are much more prone to glazing due to running at constant high speed with light loads. Generators running at 3600 rpm (60Hz) are more at risk than the generators running at 50 Hz (3000 rpm).

Larger generators are often 4 pole running at 1500 or 1800 rpm. There are less glazing issues with these.
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Old 02-25-2017, 07:38 PM   #39
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Chaser and Baker,
OK got it good now.
The "cooler" is a moderator or stabilizer. Makes me wish I had a "well designed marine engine" but since I almost never run at any other speed except 2300rpm and 50% load my little Mitsu will probably be long lived.

I have thought in the past that removal of the "oil cooler" would be quite beneficial for underloaders. But I see now the cooler in the case of underloader is a heater ... just what is needed. Could it be that a bigger "cooler" would help underoaders keep their oil temp up at low load?

This cooler sounds a bit like multi-viscosity oil. The temperature is stabilized w the cooler and the viscosity is stabilized w the MV oil.
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Old 02-25-2017, 08:01 PM   #40
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Coolant to oil heat exchangers are really elegant. At low power with thermostat closed, coolant is recirced and the oil HX is on the discharge of the water pump, between that and the block. As engine warms up, it does actually put some heat into the oil. Running at high load, the thermostat is open and lots of coolant is going through the coolant HX. This drops the coolant temp coming out of the water pump, so tends to cool the oil. And at high load there is much more heat going into the oil, so this is where you want cooling and you get it.

On little NA engines, you don't really need any oil cooling of any sort. High hp engines have piston cooling jets aiming oil onto the underside of the pistons, and this picks up GOBS of heat. Those engines absolutely need active cooling.

With the oil hx you get oil temps like 190f at light load, 210 at high load, or thereabouts. Pretty tight range, really.

I could go off on a rant about marine engines using sea water to cool lube oil, but that's another topic.
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