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Old 09-15-2011, 12:28 PM   #21
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Normal Engine RPM's

Yes ,

I have done it on our 90/90 and tho Volvo tells me I should run at 2500 under load ,

the cruise RPM to make the usual 6-6.5K (28 ft lwl) is far too high.

By proping to 2100-2200 at WOT we cruise 1600 for 6K and 1800 for as fast as we get.

Being over proped does not change the way the dual Balmars work on the start or house battery banks.

It also does not change the ability to engage the Adler Barbour cold plate mechanical drive.

It will absorb almost 10 hp warm box , but we never allow the box to get that warm .

The unit will bang the 2 plates down to -10F to solidify the 0f deg plate in 2 hours.

The box is special built so holding is 4 days , we move every 3rd , for constant temps.

The delight of cruising with as low a noise and vibration level is no where as delightful as pure sailing , but its not bad.

The sailing is not a bit harmed by the oversized prop diameter as the large 2 blade is locked behind the deadwood.

My point on setting a boat up to optomise the way the boat is used , rather than some spec the engine as if morons were at the controls will work for an owner that prefers long life and lower noise levels.

At 3/4 a gallon fuel burn , "saving" fuel is not that a big deal.

Our Volvo MD 3B is rated 35 hp cont, the 2 cylinder 25 hp and the single at 15hp.

Volvo is very conservative as all the engines are the same , cept for cylinder count.

With 3/4 a gal burn I guess the engine is cranking out 13HP or so.

13hp at 2100rpm to get 6K is too far down the power curve to load the engine.

1600 is much nicer , smooth and quiet.We set 1600, it creaps to 1800 as the batts go up and the freezer loads drop.

It does work well for me , so* I sugest it to displacement folks that wish to enjoy the advantages.

Sadly on our New England cruising we chose destinations that are about 3 hours apart , and do most sailing in our Grumman Dink.


-- Edited by FF on Thursday 15th of September 2011 12:37:08 PM
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Old 09-15-2011, 01:06 PM   #22
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Normal Engine RPM's

Quote:
nomadwilly wrote:
Hi Bob,

The EGT tells the exhaust gas temperature (if installed right) so we know how much heat is in the exhaust pipe. Can one make assumptions about what the temperature of critical engine parts are inside the engine? Say my exhaust valves are 1000 degrees when my EGT says X is the temp of my exhaust gas. Then I take the EGT off that engine and install it on another engine and run it at X EGT. Are my exhaust valves on the 2nd engine at 1000, 700 or 1200 degrees. A good temp for one engine may not be good for another. I don't know but perhaps you, Rick or David does.

*
*I think Fred has already answered this one but I'll be his echo.* I dunno what the exact*risky EGT is for your engine but the numbers are out there.* The way the commercial guys use EGT is to prevent destruction of the engine - a drop dead number as it were.* As someone has already pointed out EGT says nothing about the other critical operating temps - if somebody took my post to mean that then they need to reread my post.* The reason EGT is important in applications that can generate rapid torque demands is because EGTs can go off the scale long before the other operating temps will reflect the increased load on the engine.* As Fred has already alluded to, in an overprop situation the number would tend to be constant - once you determine what the relationship is between throttle setting and EGT you would not expect that to change over time so the gauge would provide initial information and*then be*"less useful"*over the long term.*

I think you could probably get a pretty good approximation of the EGT using an infrared thermometer.* Given that the relationship between throttle setting and EGT isn't likely to change that would probably be good enough.* Particularly so since I opened my original post by saying that I think this whole discussion is largely a tempest in a teacup.* These engines are seriously overbuilt for most of our purposes.* Their most likely failure mode - BY FAR - is operator neglect - lack of cooling water & seawater ingress being at the top of that list.* Moderate overpropping and the occasional high EGT is likely not a serious risk.* But that's my opinion and its value to you is pretty much what it cost you to obtain it.

*


-- Edited by bobofthenorth on Thursday 15th of September 2011 01:08:19 PM
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Old 09-15-2011, 02:20 PM   #23
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RE: Normal Engine RPM's

Quote:
bobofthenorth wrote:" ...the occasional high EGT is likely not a serious risk."**
That's kind of like saying the occasional*coronary*is no big deal.

The manufacturer may provide you with an exhaust temperature limit but that should never be a goal.

Extended operation at high exhaust temperatures will lead to exhaust valve failures. Period, no waffling, it will kill your exhaust valves. A poorly performing turbo charger will lead to high exhaust valve temperatures and failures even though the exhaust temperature shown on the pyrometer is within limits. That is a fact.

Using an IR thermometer to read exhaust temperature is like checking your freezer temperature from the other side of the galley. There is way too much thermal mass between the meter (which only converts IR radiation to an assumed temperature that depending on emmisivity may be way off) to tell much about the temperature of the gases departing the cylinder. Even a sensor at the turbine inlet which is 100 percent more information than 99 percent of small or medium sized marine engines will ever tell you doesn't tell you anything about the condition that is melting the #3 piston or turning the exhaust valves on #4 to expensive metal sculpture.

Unless you have*an*EGT probe installed within a couple of inches*of the exhaust outlet from*each cylinder you are only getting a snapshot of the overall loading condition and thinking that keeping that mostly below the maximum temperature the manufacturer allows at the exhaust outlet most of the time only gives you a slow motion view of your engine fading away before your eyes.

*

*
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Old 09-15-2011, 02:48 PM   #24
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RE: Normal Engine RPM's

Whatever.* I stand by what I wrote.* In the grand scheme of things high EGTs are the least of our worries.* By your assessment*most EGT probe installations are inadequate anyway.*
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Old 09-15-2011, 03:06 PM   #25
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Normal Engine RPM's

*

*I don't know how I missed commenting on this statement:

"... once you determine what the relationship is between throttle setting and EGT you would not expect that to change over time so the gauge would provide initial information and*then be*"less useful"*over the long term."

*There is no direct relationship between throttle setting and EGT. The "throttle" on your boat does nothing other than set a target speed for the governor. The governor then adds fuel to bring the engine up to that speed or it reduces fuel to bring it down to that speed.

You can set a speed and the engine will happily run at that speed until something changes that slows the boat and creates added load that slows the engine. The governor will add fuel and the EGT will rise. If the load goes up far enough or lasts long enough the EGT can reach damaging levels before the fuel limit is reached by the governor ... all the* while the engine rpm might stay the same. You can set your "throttle" at just above idle and a line or something in the prop can overload the engine without ever showing up on the tach until it drops to zero.

The relationship between "throttle position" and EGT is a rapidly changing one. High EGTs may be the least of your worries but they are the most likely cause of engine failure for those who choose to ride the wild propeller curve in pursuit of saving a dime an hour on fuel. Trying to convince others that ocassionally heating the exhaust valves to a rosy glow is Ok is not very nice advice.



-- Edited by RickB on Thursday 15th of September 2011 03:07:49 PM



-- Edited by RickB on Thursday 15th of September 2011 03:16:31 PM


-- Edited by RickB on Thursday 15th of September 2011 03:17:39 PM
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Old 09-15-2011, 03:49 PM   #26
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RE: Normal Engine RPM's

Quote:
RickB wrote:
*

*I don't know how I missed commenting on this statement:

"... once you determine what the relationship is between throttle setting and EGT you would not expect that to change over time so the gauge would provide initial information and*then be*"less useful"*over the long term."

*There is no direct relationship between throttle setting and EGT. The "throttle" on your boat does nothing other than set a target speed for the governor. The governor then adds fuel to bring the engine up to that speed or it reduces fuel to bring it down to that speed.

You can set a speed and the engine will happily run at that speed until something changes that slows the boat and creates added load that slows the engine. The governor will add fuel and the EGT will rise. If the load goes up far enough or lasts long enough the EGT can reach damaging levels before the fuel limit is reached by the governor ... all the* while the engine rpm might stay the same. You can set your "throttle" at just above idle and a line or something in the prop can overload the engine without ever showing up on the tach until it drops to zero.

The relationship between "throttle position" and EGT is a rapidly changing one. High EGTs may be the least of your worries but they are the most likely cause of engine failure for those who choose to ride the wild propeller curve in pursuit of saving a dime an hour on fuel. Trying to convince others that ocassionally heating the exhaust valves to a rosy glow is Ok is not very nice advice.
*Your analysis is correct for non-marine applications but seriously flawed for a marine situation.* Changing the prop is the only thing that is going to materially change what will be a more or less direct relationship between throttle position and EGT on a boat.* The relationship will change slightly with changing displacement and wind loading but for the world most of us live in it won't change enough to matter unless the prop is changed which I thought was the subject under discussion.

If I foul a line with a prop EGTs are likely to be the least of my worries.
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Old 09-15-2011, 04:56 PM   #27
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Normal Engine RPM's

Quote:
*

*
*Your analysis is correct for non-marine applications but seriously flawed for a marine situation.* Changing the prop is the only thing that is going to materially change what will be a more or less direct relationship between throttle position and EGT on a boat.* The relationship will change slightly with changing displacement and wind loading but for the world most of us live in it won't change enough to matter unless the prop is changed which I thought was the subject under discussion.

*

*I beg to differ on this. A fouled bottom or change in boat loading (ie "vacation load") will change EGT significantly. It*will also change WOT RPM*and that can be overloading.

I have experience in this as I had a pyrometer on my ex boat when I repowered.


-- Edited by jleonard on Thursday 15th of September 2011 04:57:00 PM
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Old 09-15-2011, 05:18 PM   #28
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RE: Normal Engine RPM's

Quote:
bobofthenorth wrote: Your analysis is correct for non-marine applications but seriously flawed for a marine situation.* etc
Wow, there isn't much point in continuing this conversation.

Having spent a few thousand hours watching cylinder pressures, exhaust gas temperatures, torque and fuel flow change with load at constant rpm in real time on an engine control computer while crossing the Pacific more than a few times I guess I didn't realise that the engine was not connected to a prop.

*
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Old 09-15-2011, 09:12 PM   #29
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RE: Normal Engine RPM's

Quote:
RickB wrote:Wow, there isn't much point in continuing this conversation.
Having spent a few thousand hours watching cylinder pressures, exhaust gas temperatures, torque and fuel flow change with load at constant rpm in real time on an engine control computer while crossing the Pacific more than a few times I guess I didn't realise that the engine was not connected to a prop.
And these real time load changes were on just exactly which recreational trawler power train?

I have to say though - I can readily agree with your opening sentence.* I started out thinking this whole discussion was a tempest in a teacup - now I'm convinced.
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Old 09-15-2011, 10:34 PM   #30
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RE: Normal Engine RPM's

So**** .....it seems overpropping is done to save fuel** ...that's what I'm hearing.* FF mentioned a reduction of noise but everybody else is focused on fuel burn. David M has been a very objective source of engine knowledge for a long time and he says fuel savings is about 10%. Marin was overpropped some time ago and then got propped right and I think he said his fuel burn remained about the same. Anybody recall? I'd rather do best by my engine and burn a bit more fuel if that's the case.
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Old 09-15-2011, 10:36 PM   #31
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RE: Normal Engine RPM's

boatk9,

"Never mind....better*solution is to convert the engines*to NA."

BAD idea.
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Old 09-16-2011, 03:50 AM   #32
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RE: Normal Engine RPM's

Quote:
bobofthenorth wrote:And these real time load changes were on just exactly which recreational trawler power train?
*If you honestly believe that there is a separate set of physical laws that apply only to diesel engines when operated for recreational purposes then there really is no point in your being involved in this discussion.

I think you missed jleonard's comment as well.
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Old 09-16-2011, 05:20 AM   #33
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RE: Normal Engine RPM's

I also do not believe there is much if any significant fuel savings by loading the engine harder and running a lower rpm. A diesel is a pretty precise machine. It uses fuel to make horsepower, and since it takes X hp for a given boat ot go a certain speed, the fuel consumption will be the same. I will also theorize here that perhaps heavily loading "might" actually use MORE fuel, because the extra loading will certainly raise EGT (still might be within the max spec) and a higher EGT would indicate an energy loss.

As far as noise and vibration levels, in the boats I have run I really have never noticed much difference from 1600 to 1900.

Actually the turbocharged engines I have run are MUCH quieter when cruised over 1800 RPM because the turbo does help*quiet the exhaust noise once it starts producing some boost. (plus there is more water being pumped into the stream).

Anywho, my boats will always be propped within mfg specs based on*my experience and my knowledge. And I hope I can avoid buying a boat that had been overpropped for any significant part of it's life.

By the way one of my (many) winter projects is to replce the exhaust elbow on the FL120 and I will be adding a pyrometer
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Old 09-16-2011, 09:38 AM   #34
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RE: Normal Engine RPM's

"I will also theorize here that perhaps heavily loading "might" actually use MORE fuel, because the extra loading will certainly raise EGT (still might be within the max spec) and a higher EGT would indicate an energy loss."

Got it backwards J, the higher temps are a sign of a more efficient engine.Up to a point.

Higher EGT is better as our engines are all heat pumps of a sort .

Look up Evans Coolant , and you will find many of the class 8 trucks installing 235f thermostats , to increase the operating temps and the efficiency.

Believe me the guys that burn 700 or more gallons a week are willing to try modern concepts to stay afloat.
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Old 09-16-2011, 09:49 AM   #35
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RE: Normal Engine RPM's

Quote:
FF wrote:
"I will also theorize here that perhaps heavily loading "might" actually use MORE fuel, because the extra loading will certainly raise EGT (still might be within the max spec) and a higher EGT would indicate an energy loss."

Got it backwards J, the higher temps are a sign of a more efficient engine.Up to a point.

Higher EGT is better as our engines are all heat pumps of a sort .

Look up Evans Coolant , and you will find many of the class 8 trucks installing 235f thermostats , to increase the operating temps and the efficiency.

Believe me the guys that burn 700 or more gallons a week are willing to try modern concepts to stay afloat.

*Yes up to a point, and that's my point.* And coolant temps are different than exhaust gas temps.
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Old 09-16-2011, 10:16 AM   #36
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RE: Normal Engine RPM's

boatk9,

First of all you'd need to pull the head and remove enough metal to raise the compression ratio to NA levels or the engine would be much less efficient. How much to remove??? One may need to shave the block to remove enough. And then the valves may hit the pistons or run too close and too hot. Some of this may not be true but you'd really need to know what your about to be successful. First things first as I see it and that would be to run the turbo until it needed enough attention to objectively consider a conversion. As DAvidM says (usually) take it to BoatDiesel.
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Old 09-16-2011, 10:49 AM   #37
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RE: Normal Engine RPM's

If* you ever intend to sell or buy a boat, one of the basic tests during sea trial is to assess if the engine can achieve full rated RPM without overheating. Obviously an over propped boat will overheat.*This then creates anxiety and the boat remains unsold until a brave soul shows up that believes no damage was done during the many hours of operation the boat was improperly set up with too big a prop.

The long and the short of it, given the little downside associated with proper sized props, ignore the cruising prop stuff if you want to buy or sell a boat.
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Old 09-16-2011, 01:33 PM   #38
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RE: Normal Engine RPM's

Quote:
nomadwilly wrote:First of all you'd need to pull the head and remove enough metal to raise the compression ratio to NA levels or the engine would be much less efficient. How much to remove??? One may need to shave the block to remove enough. And then the valves may hit the pistons or run too close and too hot.
*

I'm not advocating converting any engine from turbo to non turbo but it isn't quite that bad. The 3208 mentioned has a c/r of 16.5:1, the n/a version is 18.2:1. Both start as normally aspirated engines and if a diesel has enough compression to start, it has enough to run.

The important differences and major consideration as far as economy goes is the cam, piston style, and injection pump/injectors.

Among those, the cam and fuel injection are biggies, turbo engines use valve overlap for valve cooling, n/a engines don't so volumetric efficiency falls pretty low*and the useful power available will be pretty*small before you start making some serious smoke.
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Old 09-16-2011, 02:17 PM   #39
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RE: Normal Engine RPM's

boatk9,

I just thought of another thing that may need to be replaced** .....camshaft. Very likely a turbo'd engine will/would require different valve lift and timing* ...most likely the latter.
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