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Old 03-19-2016, 04:34 PM   #21
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Under loading.

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Originally Posted by BandB View Post
One more potentially dangerous generalization.

Not sure if you were referring to me, but Bob Smith is supposed to know Lehman's as he was the guy that developed the marinization of them and he presumably developed his ideas after spending considerable time at the factory and working with the engineers there.

I looked through my notes I took over the two times I took his course and he mentioned that boats boats in the PNW have the potential to operate "too cool". That discussion came up recently during another thread. He talked about having a "piss line" [what he called it] to another thru hull, that would bypass some of the raw water flow away from the heat exchanger but that option was never developed. So, he said to just run the engine at 1800. I remember pressing him on this topic.


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Old 03-19-2016, 04:47 PM   #22
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Ski

My sense is that too many people get paid to write articles that are of interest and appeal to the general boating public. That does not mean the articles are factual for all engines. My friends in the same business as you find under loading a "modern" propulsion engine is overhyped. Does your experience find the DD 2 strokes suffer any under loading issues?
To butt in a bit, as an experienced DD user, who has had the good fortune to know three excellent and experienced DD mechanics and many fellow users:

No, they don't. The protocol is to run them up to about 80% of WOT for a little while if they have been at low speeds for several hours; in most cases they will smoke a bit and clear up. The key is not to run them at no load idle for more than a few minutes.

One thing I like about modern electronic engines is they are more tolerant of low speed operation. Whether that applies to no load, I don't know.
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Old 03-19-2016, 06:11 PM   #23
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Not sure if you were referring to me,
I wasn't. Actually I was referring to the potential of people taking Steve's article or any of what has been typed here and assuming that it applies to their engines in the exact same way.
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Old 03-19-2016, 10:03 PM   #24
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I have na Hinos I run around 30% to 65% while cruising mostly 30-35%, at the end of the day I run up to wot for maybe 5 minutes. This tells me that the engines will reach wot and all is well with the hull,running gear and the engines aren't being overloaded.


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Old 03-19-2016, 11:06 PM   #25
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I am still confused as to how to determine % Load. I know it isn't rpm but how? Is it the amount of hp being produced, i.e. If the engine is dated for 300hp and based on manufacturers curves show you are producing about 100hp is that 33% loading?
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Old 03-20-2016, 07:15 AM   #26
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The above graph is one of many obtained by google "fuel map for diesel engine"

Yes ,its for a car engine , but the concept is correct for any diesel.

Setting the vessel up to cruise in the bulls eye will be the most efficient that boat can do with that engine.

Yes it will have sufficient load not to die early.

Comparison between engines can be done , which is why boat engine folks do not supply this style info.

A tutorial,

https://www.morganscloud.com/2015/06...gine-fuel-map/
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Old 03-20-2016, 07:52 AM   #27
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Steve:


Thanks for your explanation. I think all of us could use an objective set of criteria for determining when we are under loaded, or maybe more useful- criteria that would indicate than an engine is properly loaded. So let me propose some, taken from your article and your posting above:


1. Coolant temperature at 160 F or above.
2. Oil temperature at 180 F or above.
3. Exhaust turbo only has a light dry soot coating (we can't easily see injector tips or ring carbon, but turbo soot should be a decent indicator).
4. Oil analysis shows less than 0.5% fuel content.


I believe that these criteria will tell you if you are loaded decently. On my Yanmar 370, I meet all of these criteria with the possible exception of oil temperature while running at about 1,600 rpm and producing roughly 60 hp with occasional high power runs to blow out the accumulated soot.


David
The only criteria I would add to this is exhaust gas temp above 450-500F. An exhaust gas probe would tell you this, but that's not something most folks have or will add. Alternatively you could shoot the dry portion of the exhaust elbow immediately after the elbow with an IR pyrometer for a rough reading on EG temp.

The coolant should always reach and ultimately run at the thermostat's rating. If it's more than a few degrees lower while under load something is wrong.

The turbo soot accumulation is pretty subjective, one man's build up is another's patina. And, unless it's disassembled, you can only see the intake turbine on the turbo, not the portion that operates in the exhaust gas stream, and that's where soot, and un-burned fuel would accumulate.

Additionally, fuel dilution is dependent on the lube time, the number of hours on the oil. Some engine manufacturers limit the absolute fuel dilution to 5%, however, if that occurs after 70 hrs then that's problematic (and the oil would need to be changed), while if it occurs after 200 hours then it's far less of an issue. I have clients running displacement trawlers, powered with common rail engines, using synthetic oil, doing oil changes at 450 hrs (this is within the manufacturer's spec's provided you use syn oil), practicing the periodic run up, with no appreciable fuel dilution or other contamination showing up in the oil analysis other than a slowly falling TBN number, which is normal, the threshold for which is 2.5.
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Old 03-20-2016, 08:02 AM   #28
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I am still confused as to how to determine % Load. I know it isn't rpm but how? Is it the amount of hp being produced, i.e. If the engine is dated for 300hp and based on manufacturers curves show you are producing about 100hp is that 33% loading?
In most cases, if your engine doesn't have a load % indicator, then you can rely, roughly, on % rpm of rated wide open throttle (WOT). For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load. Load and rpm curves are not superimposed on each other, they diverge but not significantly. Bottom line is the 75% number isn't terribly critical, it need not be exactly 75%, that's a figure I use to ensure the engine is loaded while on sea trials, for realistic temperature measurements.

Before doing any of this, however, make certain your engine reaches rated WOT under load. Ideally it should exceed this rated number by 20-40 rpm, i.e. using the above example 3030 would be ideal, which tells you the engine isn't overloaded (acutely, this can kill an engine far quicker than under-loading), and that your prop is properly matched to the engine. If your engine doesn't reach rated WOT rpm find out why, and propeller adjustment should be the last option. Before that check injectors, valve adjustment, fuel supply and exhaust back pressure. I've encountered excessive back pressure on vessels fresh from the builder, so don't rule that out on a new vessel. In many cases, a prop pitch reduction only masks other problems, and when this is done it essentially de-rates the engine, you aren't getting the HP you paid for.
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Old 03-20-2016, 08:13 AM   #29
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One aspect not mentioned in the article is this problem is magnified by raw water (seawater), as opposed to jacket water (coolant), cooled after coolers. Raw water after-cooled engines have broader performance capabilities, however, they require cooler combustion air to meet nitrogen oxide emission guidelines, which means the intake charge air is often too cool for ideal combustion at light loads, exacerbating wet stacking, carbon fouling and soot accumulation.
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Old 03-20-2016, 08:49 AM   #30
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Lots of advice, contradictions and guesses on this thread, some of it hopefully accurate. To cut to the chase, and gensets aside - provided the vessel is propped correctly, relevant temperatures are achieved, 65 to 75% power (rated fuel burn not RPM) achieved now and then and maintenance is up to snuff - it seems under loading issues can be set aside.

Confusing things a bit more, does anyone remember all the discussion a year or so ago instigated by a different marine writer about the benefits of over propping?
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Old 03-20-2016, 10:31 AM   #31
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"relevant temperatures are achieved"

If oil temp is critical to long and happy low load engine life there are any number of thermostats that can be used to bypass the oil cooler for the desired temp.

An Auto style EGT gauge is east to install, and the newest are NOT critical to the sense wire length.

$ 112. or so free shipping.

GlowShift EGT Gauge - Amazon.com‎

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Old 03-20-2016, 10:51 AM   #32
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Quote:
Originally Posted by Steve DAntonio View Post
In most cases, if your engine doesn't have a load % indicator, then you can rely, roughly, on % rpm of rated wide open throttle (WOT). For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load. Load and rpm curves are not superimposed on each other, they diverge but not significantly. Bottom line is the 75% number isn't terribly critical, it need not be exactly 75%, that's a figure I use to ensure the engine is loaded while on sea trials, for realistic temperature measurements.

Before doing any of this, however, make certain your engine reaches rated WOT under load. Ideally it should exceed this rated number by 20-40 rpm, i.e. using the above example 3030 would be ideal, which tells you the engine isn't overloaded (acutely, this can kill an engine far quicker than under-loading), and that your prop is properly matched to the engine. If your engine doesn't reach rated WOT rpm find out why, and propeller adjustment should be the last option. Before that check injectors, valve adjustment, fuel supply and exhaust back pressure. I've encountered excessive back pressure on vessels fresh from the builder, so don't rule that out on a new vessel. In many cases, a prop pitch reduction only masks other problems, and when this is done it essentially de-rates the engine, you aren't getting the HP you paid for.
Sorry for the long quote. It it a pain to do on the iPad I am on.

Thanks again Steve. I am very interested in all of this stuff right now as I;
a) have no experience with Diesel engines beyond smallish sailboat diesels.
b) I have an offer on my first power boat and a survey coming up in a couple weeks.

I have a Cummings mechanic doing the mechanical survey and he will be able to check everything out but I am trying to glean as much info as I can in the meantime so I can try to better understand what the heck he will be trying to tell me.
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Old 03-20-2016, 12:18 PM   #33
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I am still confused as to how to determine % Load. I know it isn't rpm but how? Is it the amount of hp being produced, i.e. If the engine is dated for 300hp and based on manufacturers curves show you are producing about 100hp is that 33% loading?
Short answer, yes.

Assuming it is propped to reach rated wot rpm the prop curve shows the load vs rpm. As you can see it is very non linear. In fact the perkins chart above tells us it was calculated based on a 2.7 exponent. If you plot the curve
(rpm /wotrpm)^2.7= you will reproduce the prop curve. You can just plug that equation into google search and it will do all the work.

The above exponent is a guess by the maker and some use 2.5 to represent how the typical propeller loads the engine.
The best measure, unless you have electronic systems, is actual fuel used vs max fuel use.
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Old 03-20-2016, 12:50 PM   #34
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Quote:
Originally Posted by Steve DAntonio View Post
In most cases, if your engine doesn't have a load % indicator, then you can rely, roughly, on % rpm of rated wide open throttle (WOT). For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load. Load and rpm curves are not superimposed on each other, they diverge but not significantly.
.
Our main engines do diverge significantly. If we ran at 75% RPM, we would be well below 75% load. On our generators with much smaller engines the difference between the curves is less. However, with any sort of a performance chart and fuel consumption chart it's easy enough to approximate the load.

Edit:

I just quickly looked at our data on several engines, all on planing hulls. Interesting as our maximum cruise target is 80%. So, 80% load is the following percentages of RPM. 87%, 89%, 88%, 89%, 88%, 88%, 92%, 88%, 90%.
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Old 03-20-2016, 01:08 PM   #35
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Steve D wrote;
"For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load."
Steve tell us this is a typo.
I have a 3000rpm engine and consider it 50% loaded at 2300rpm.
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Old 03-20-2016, 01:30 PM   #36
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Steve D wrote;
"For instance, an engine rated at 3000 rpm WOT, would be run at 2250 for 75% load."
Steve tell us this is a typo.
I have a 3000rpm engine and consider it 50% loaded at 2300rpm.
I can't believe he wrote that. Taking the same engines I did above, at 75% RPM here would be their loads:

% Load at 75% RPM: 51%, 48%, 50%, 52%, 51%, 52%, 47%, 55%, 52%.

That is a huge difference and, in my opinion, running at those loads would not be an adequate sea trial. Hopefully, he'll correct himself.
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Old 03-20-2016, 01:46 PM   #37
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I can't believe he wrote that. .
Elementary issue with self anointed experts. Once again, it illustrates need to pick your information sources carefully. Which is why many of us go to engine maker, boat diesel and proven hands on (issue specific) yards and mechanics.
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Old 03-20-2016, 02:26 PM   #38
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That's a low one Tom.

"self anointed"?
I believe it was PMM that "anointed" Steve. But he was probably well anointed before that.
I have high regard for him.
But then I'm probably self anointed.
Sounds like a religious high.
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Old 03-20-2016, 03:27 PM   #39
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That's a low one Tom.

"self anointed"?
I believe it was PMM that "anointed" Steve. But he was probably well anointed before that.
I have high regard for him.
But then I'm probably self anointed.
Sounds like a religious high.
Wifey B: Is "self anointed" a form of masturbation?
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Old 03-20-2016, 05:08 PM   #40
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Greetings,
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