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Old 03-23-2016, 05:49 PM   #101
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Gordon:


Buy your engine zincs and your hull zincs from boatzincs.com. They don't have to come from Cummins. You just need to know the size- 1/4", 3/8", etc. Buy the zinc only rather than the zinc plus brass cap. And tighten the zinc with pliers so it won't unscrew and get stuck inside the exchanger.


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Old 03-23-2016, 07:54 PM   #102
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Ski, a TF member and a mechanical engineer who now practices as a marine diesel mechanic, posted the following in reply to Gordon's thread on boatdiesel.

We now have two full time professional mechanics who are saying that under loading is not a problem on propulsion engines.

"Second Tony on this. In 20+ years in the engine business I have never seen a propulsion engine that suffered from light load running. Only two gensets that had high blowby from glazed cylinders, those probably never got any decent break in. But never seen an issue on a propusion engine.

Advocating 75% power is nuts. Most engines 20-30% keeps them happy. 75% is usually considered an upper limit for long term use, not a minimum. 75% is a good number for the end of the trip "clean out", though. No need at all to go to 100% unless you want to check for correct max rpm.

Running light will gunk up the exhaust manifold, piston crowns and turbo. But one hard run will clean that right up. Not an actual problem. It is cured when that cloud of smoke on power-up goes away.

If you power up and see little or no smoke, then engine was NOT gunked up from your previous light load run.

I have seen dry stack mufflers clogged with soot from light load running, enough to choke the engine and require muffler replacement or worse, a stack fire. But that only applies to dry stack, is rare, and usually causes no engine problem. Sometimes with careful hard runs we can "burn them clean", but have had to replace a couple mufflers."


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Old 03-23-2016, 10:25 PM   #103
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[QUOTE=djmarchand;426779] Only two gensets that had high blowby from glazed cylinders, those probably never got any decent break in. But never seen an issue on a propusion engine
QUOTE]

One thing I've always been told on marine engines is to go 100% by the book on break in and that's in many ways the most critical time in the life of your engine.
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Old 03-24-2016, 10:56 AM   #104
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One thing I've always been told on marine engines is to go 100% by the book on break in and that's in many ways the most critical time in the life of your engine.
You are absolutely right. Here are the break in instructions from Northern Lights:

BREAK-IN PERIOD

1. The first 100 hours on a new or reconditioned

engine are critical to its life and performance.
2. Operate the engine under various conditions,
particularly heavy loades with minimal idling, to
help seat engine components properly.
3. Constantly check the engine temperature and oil
pressure gauges (sets with Series 3 or 4 panels).
4. Oil consumption is greater during break-in as
piston rings take time to seat.



These are fine as far as they go. But I really appreciated Jeff (I think his name was- at Bayshore Marine) cautioning me about maintaining load on the genset during break in and suggesting ways to do it as well as advice afterwards.

It was Jeff who told me that he keeps one guy busy removing gensets and honing the cylinders to fix those that have been run 24/7 in the Carribean over the winter when it really isn't needed. Maybe an exaggeration based on Ski's experience, but worth noting in any case. Gensets are different because while they run at decent rpms, there is often zero load on them.



Nothing beats hands on practical experience from guys like Jeff, Tony and Ski.

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Old 03-24-2016, 12:35 PM   #105
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All this talk about the unknowns of underloading. I suppose overloading isn't such a mystery since the mfg's post relatively clear guidelines regarding M1, M2 ratings, etc.
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Old 03-24-2016, 01:18 PM   #106
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All this talk about the unknowns of underloading. I suppose overloading isn't such a mystery since the mfg's post relatively clear guidelines regarding M1, M2 ratings, etc.
Underloading in the trawler world. Overloading in the performance boat segment.
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Old 03-24-2016, 01:25 PM   #107
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Iím gratified that this subject has generated so much dialog and exchange of information and opinions. I have the greatest respect for Tony, I have corresponded with him on several occasions and I have been a commercial member of BD for many years. I respectfully disagree with some of his tips, including propeller nut installation order, it flies in the face of ABYC, USN, USCG and SAE guidelines (I write an entire column on this subject). I completely agree with his assessment of exhaust system issues being very problematic, (especially for heavily loaded engines). His website is a trove of valuable, practical information.

He acknowledges but downplays under loading issues, and I don't doubt what he says is accurate. His experience is with west coast vessels, mostly Cummins and a lot of commercial/fishing vessels, few of which putt about at low load, and because there are far fewer places to do this in that region. While on the east coast the intracoastal ww and many tributaries are low load havens.

I'm on different vessels every week with many different engines, Deere, Lugger, Cummins, Cat, MAN, MTU, 2 stroke DDs, Perkins, Westerbeke, Yanmar, Volvo, the gamut. All are recreational, most displacement some planing (and these run at displacement speeds most of the time), some dry stack, a few sail. Again, different than Tonyís experience and perhaps that of other cited diesel mechanics.

The effects I'm seeing, when I see them, the effects I write about and photograph, don't typically stop an engine per se, they are more insidious, they lead to rough running, smoking, poor fuel economy, fouled injectors and turbos and long term potential for oil starvation and thereby premature wear of lubricated parts, that are often not directly attributed to chronic under loading.

These aren't offset by the occasional high speed run, you can't turn the clock back on hundreds of hours of low load soot and varnish accumulation with one high speed run. I advocate a periodic heavier load for 10 mins out of every 4 hours. This is in no way harmful to any diesel engine unless it has other issues. BTW, Cummins and other manufacturers make continuous duty engines that are designed to run at 100% load 100% of the time, other ratings limit 100% load to 10 minutes, it varies from engine rating to engine rating.

You can cast about for opinions until you find the one that fits your view and experience, I don't fault anyone for doing this, it's reasonable. I'm simply reiterating that my observations, and the articles I write based on them, are based on my own first-hand experience, which Iíve only augmented in this case with input from engine manufacturers and volume re-builders.
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Old 03-24-2016, 02:18 PM   #108
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Hi Steve,

From the little that I understand, I don't think that you would get much of an argument from Tony Athens on a higher loading for 10 minutes every few hours. Few of us have the luxury of specifying the engine that is in our boats. We buy a boat that will best meet our needs and it is an exercise in compromise.

I am looking at buying a boat and the one that I have an offer on has a larger engine than I wish it did. However, the Cummins QSB 5.9L is very common in SD hulls of this size. As an owner, I will be balancing a number of factors when selecting a throttle position. Fuel burn will be an important one. The prior owner ran the boat at typically 10 knots from what he told me. He would have burned 3-4 times the fuel as he would have at the more sedate 7 knots that I anticipate. He has, literally, money to burn. I don't. So as a future owner I will have to balance current operating costs, with potential future rebuild or maintenance costs. So while it might be "best" for engine life to run at 50-70% loading for most of the time, I will likely end up running at about 30% load much of the time. However, based a lot on what I have been learning from folks with actual experience like you, I will also try to modify my use in ways to try and be a little easier on the engine.
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Old 03-24-2016, 04:56 PM   #109
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Dave you're in the drivers seat now as a shopper. When you actually buy a boat you will no longer be in control. For the most part. Of course you can buck up and run 50 to 65% load w no need to blow out any black stuff or whatever you want but the fallout will be on you. I'm not that familar w what boat you're looking at and what the options would be if you bought it. And there are few SD boats out there power loaded ideally for slow running. The single engine GB36 or 42 comes to mind. When boats are bought new the people buying them have plenty of money for fuel at any speed but as they get old and cheap people who buy them have limited money for fuel.

But there are boats out there that are propperly powered for slow running. Even some from the 70's. You gotta shop rather hard to find them though. If I were you, and of course I'm not, I'd find some boats that are powered for what you want to do. And when you buy such a boat participation in discussions such as this thread you can participate w nothing to loose. Just take part because it's interesting.
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Old 03-24-2016, 05:04 PM   #110
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Hi Steve,

From the little that I understand, I don't think that you would get much of an argument from Tony Athens on a higher loading for 10 minutes every few hours. Few of us have the luxury of specifying the engine that is in our boats. We buy a boat that will best meet our needs and it is an exercise in compromise.

I am looking at buying a boat and the one that I have an offer on has a larger engine than I wish it did. However, the Cummins QSB 5.9L is very common in SD hulls of this size. As an owner, I will be balancing a number of factors when selecting a throttle position. Fuel burn will be an important one. The prior owner ran the boat at typically 10 knots from what he told me. He would have burned 3-4 times the fuel as he would have at the more sedate 7 knots that I anticipate. He has, literally, money to burn. I don't. So as a future owner I will have to balance current operating costs, with potential future rebuild or maintenance costs. So while it might be "best" for engine life to run at 50-70% loading for most of the time, I will likely end up running at about 30% load much of the time. However, based a lot on what I have been learning from folks with actual experience like you, I will also try to modify my use in ways to try and be a little easier on the engine.
To me, it's all about condition and how it surveys. The fact you'll be running it mostly at 30% load doesn't concern me. You can go faster occasionally just to keep a smile on it's face. However, there are plenty of other things to check out on the engine that are more worrisome than what load you intend to run. Just don't let all this talk discourage you from choosing it if it's the right boat for you.

And, someone mentioned all the talk about low load and none about high. Well, I lived on a lake until 2012. Far more problems there with high load. There were people who only knew wide open throttle. I've seen a dealer go through great detail on proper break in and then seen the boat out racing ten minutes after it pulled away. I know one dealer who on high performance boats wouldn't deliver them until he'd done some initial break in because he knew people buying fast boats often just couldn't wait. I was also amazed how well many of the engines took the abuse they received.
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Old 03-24-2016, 05:18 PM   #111
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Here is some interesting info from another engine expert about oil, temperature and light loading.......


First off, the reason a certain minimum oil temperature is desirable is because oil is designed for a certain viscosity at normal operating temperatures. Proper lube oil flow (pressure and rate) requires a certain viscosity to obtain. Too high a temperature and the oil is too thin to handle high loads. Too low a temperature the oil will either not flow or it will not flow at a rate high enough to maintain bearing clearances at high loads.

Cold oil at low loads is not a disaster. When engines are run at low loads, the internal friction of the oil itself is reduced so less heat is produced, less fuel is burned so less heat is produced and transferred to the oil but since loading is low the flow rate requirement is also reduced and oil pressure is probably higher due to the increased viscosity. Low oil temperature may mean the engine is not operating at its highest efficiency because it takes more power to move the oil around and drag created by higher viscosity oil is greater ... so less power goes to the shaft than with hot oil. So what? The engine is operating at low load, what is there to lose?
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Old 03-24-2016, 05:22 PM   #112
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Why is it that turbochargers have made under loading such a problem. Eric you say that single engine Grand Banks would not be a problem with under loading at moderate rpms and I agree. These were first delivered with Ford Lehman engines and later with Cummins 6B engines. Both engines are approximately 6 liters.


So fast forward to today where Dave is considering a boat with a Cummins QSB 380, also a 6 liter engine. The only difference between it and the Lehman is a high output turbo charger and an after cooler. The only difference between it and the Cummins 6B is a higher output turbo charger and a sea water after cooler.


Why does the addition of a turbo charger and after cooler or a higher boost turbo charger and a sea water after cooler mean that the QSB will be "under loaded" at moderate rpms and will carbon up, but the two older engines won't? All three engines will produce the same power to go the same speed in a GN 36 or similar hull.


It seems that Steve is focusing on percentage of rated power to determine whether an engine is under loaded and not actual hp per liter produced which I believe is the correct way of looking at it. I believe that any marine engine loaded to 10 hp per liter will not be under loaded.


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Old 03-24-2016, 05:24 PM   #113
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Here is some interesting info from another engine expert about oil, temperature and light loading.......


First off, the reason a certain minimum oil temperature is desirable is because oil is designed for a certain viscosity at normal operating temperatures. Proper lube oil flow (pressure and rate) requires a certain viscosity to obtain. Too high a temperature and the oil is too thin to handle high loads. Too low a temperature the oil will either not flow or it will not flow at a rate high enough to maintain bearing clearances at high loads.

Cold oil at low loads is not a disaster. When engines are run at low loads, the internal friction of the oil itself is reduced so less heat is produced, less fuel is burned so less heat is produced and transferred to the oil but since loading is low the flow rate requirement is also reduced and oil pressure is probably higher due to the increased viscosity. Low oil temperature may mean the engine is not operating at its highest efficiency because it takes more power to move the oil around and drag created by higher viscosity oil is greater ... so less power goes to the shaft than with hot oil. So what? The engine is operating at low load, what is there to lose?


I am no engine guy but I do know the backyard mechanic suggestions/theories to be way off base and those suggested by engine pros and how they mirror the vessel engineers I work with on commercial vessels. Take heed of the above and what Ski and few others post. Try and sort out the guys who keep trying to match marine engines with their cars.
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Old 03-24-2016, 05:35 PM   #114
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It seems that Steve is focusing on percentage of rated power to determine whether an engine is under loaded and not actual hp per liter produced which I believe is the correct way of looking at it. I believe that any marine engine loaded to 10 hp per liter will not be under loaded.
Interesting point that I hadn't really thought about. The Turbo enables higher HP for a given engine displacement.

I am really not concerned about using the QSB 5.9L at low power settings at this point. This particular engine has performed very well in this application for a number of years. However, the discussion has definitely improved my understanding of diesel engines in general.
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Old 03-24-2016, 06:45 PM   #115
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Interesting thread. I was rereading the operation and maintenance manual for the Cummins 6bta last night, and found a couple of things of interest. There is a warning not to operate at slow idle after a cold start for more than 10 minutes, citing the consequences discussed here. There is also a warning against extended operation below normal operating temperature, which is 181 - 203 Fahrenheit. That's all I could find regarding this subject.

One other interesting finding is that in this motor the oil cooler is in the fresh water cooling loop. So I'm not going to lose any sleep over not measuring oil temperature. In a steady state of operation oil and coolant temperature will always be very close to one another.

My conclusion from this and the various points raised here is that if I run my 6bt within the specified operating temperature (as measured by coolant temp) in steady state operation it is not going to suffer from any negative consequences related to underloading.
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Old 03-24-2016, 07:21 PM   #116
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Versions of the Cummins 5.9 fitted here appear to have rated outputs from 220hp to 380hp. Is the engine underloaded if the turbo and associated tweaks to increase max output are not fully employed? It`s still the same block and head, maybe with a few power increasing tweaks.
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Old 03-24-2016, 07:32 PM   #117
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That kinds of bring everything back to simply measuring temperature of the operating engine with an IR thermometer. If the oil pan, transmission, coolant jacket are all at the desired temperature in normal operation, I don't think I would lose any sleep over it. My engine has 4800 hrs on it. The last 5 years under the previous owner it never went over 1600 rpm. Rumor had it that there was a throttle block that was put in by the previous previous owner when it was in a charter fleet. Being somewhat mechanically inclined I discovered the problem was a binding throttle cable which was corrected in about 5 minutes with some spray lube (I have a spare if I need it). On the first WOT test, the engine spooled up to 2650 RPM and the boost gauge went up over 20 PSI. The previous owner didn't think the boost gauge worked. During the high speed run I didn't see any black smoke coming out the back. After running 900 miles at between 1250 and 1600 RPM I ran it up again to WOT and still no smoke.

At 1800 RPM, the turbo is just starting produce boost. The Cummins engine performance curve shows I should be generating about 150 HP at that point. Essentially the next 800 RPM gives me almost 270 HP. At 1800 RPM I am hitting about 9.0 knots or about .3 knots over hull speed. I guess you can look at loading two ways, before the turbo becomes effective and after. At 1250 RPM I am using a little less than 1/3 of the available HP before the turbo becomes effective but a little more than 1/10 of the available HP with the engine at WOT. Am I running 30% load or 10% load? Does the engine really care?

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Old 03-24-2016, 08:50 PM   #118
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For heaven's sakes...all this overload, underload...what happened to the Wombling free bit, enjoying life out there..? All this talk is making everyone anal retentive OCDers..!

Just run your boat at its sweet spot, whatever that is...make sure she's up to normal temp, and enjoy..! In my case with trusty Lehman 120hp, 5000 hrs plus - don't know exactly because the hr meter died years ago - she come to 85-90ļC, ( I wish you guys would get up to speed with your units), and sits there at 1800rpm, and has done so all its life. I doubt it has had its neck wrung to WOT very often, certainly not by me, as I hardly ever do 4 hrs straight running at a time anyway, and she still runs sweetly and smokeless, and uses hardly any oil. So, what does that tell you..? Just stop worrying about it, ok..?
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Old 03-24-2016, 09:35 PM   #119
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For heaven's sakes...all this overload, underload...what happened to the Wombling free bit, enjoying life out there..?
...
An obscure reference that this Brit got!

And I happen to agree that we're well off into OCD territory here. But if this is everyone's biggest concern then they're in good shape!

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Old 03-25-2016, 01:48 AM   #120
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An obscure reference that this Brit got!

And I happen to agree that we're well off into OCD territory here. But if this is everyone's biggest concern then they're in good shape!

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I knew there'd be some...
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