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Old 02-09-2013, 08:28 PM   #81
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Rick--- i'm curious... An old engine like our FL120s do not have any EGT info in the operations manual. The EGT gauges on our boat were marked with little colored tape wedges by a previous owner to show the normal reading at cruise rpm. But I have no idea if this what the reading should be although my guess is it's in the ballpark. Is there any reference you're aware of that would give an idea of what the EGT range should be for this type of engine?

I realize there are a lot of variables from where the probe is located to the prop and what kind of load the engine is seeing. So perhaps if the manufacturer did not provide an EGT range from their own tests its not really possible to know what it should be.
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Old 02-10-2013, 08:21 AM   #82
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But if you measured the thrust at a reduced rpm like 1500 to 1700rpm I think the larger prop/lower geared boat would loose more (as a percentage) of thrust than the smaller/faster prop boat. The low geared big prop unit at half speed should have less thrust.

The thrust required to move a boat at a set speed does not change because of prop diameter.

Producing the required thrust at slow (under 10K) is always more efficient with the largest diameter that will fit under the boat that it can be geared for..

This assumes the number of blades and blade width is also optimized.

As an example a ride on a tug (HUGE PROP and frequently 6-1 gearing) will show the engine is slowed very little to cut speed while free running .

Going from 10K to 5K does not require half RPM, just far less thrust.

Run a bunch of props thry Skenes to see how Diameter is king of thrust efficiency.
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Old 02-10-2013, 08:46 AM   #83
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So perhaps if the manufacturer did not provide an EGT range from their own tests its not really possible to know what it should be.
If the manufacturer doesn't provide a maximum, the best way to set a limit is to load the engine as high as possible - do a bollard pull test for example - and record the highest temperature displayed. That will give you a ballpark for the "top of the green" at least.

There is a standard figure of 900F for 4 stroke normally aspirated diesels that is used by exhaust systems and components manufacturers. This is the one I use:

http://www.asia.donaldson.com/en/exh...ry/1053747.pdf

I have found that the normal operating exhaust temperatures are quite a bit lower. That finding is based on attaching a thermocouple and datalogger on the exhaust elbow or turbocharger outlet where there is usually a convenient port.

Just pulling a figure out of my butt, I would guess your EGT would be between 600 and 700F at maximum load and down to around 200 at no load. Close?

Good timing on that question as I have been doing a lot of work on particulate filter specs for generators so have quite bit of data available. Soot, smoke, and stink are becoming big problems with yachts and we are soon going to be regulated.

(Note to certain other readers: Don't bother to come back with a rant against DPFs installed on road vehicles. I know all about it and really don't care.)
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Old 02-10-2013, 10:57 AM   #84
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The first indication of overload is increased EGT. So, if your temperatures are remaining well below the maximum allowed you should be OK.

What engine do you have? The reason I ask is I would check that the EGT limit is measured at the turbo outlet where it is relatively cool compared to the turbine inlet. The TIT is the highest you will measure, it reads higher than there than a pyrometer installed in the exhaust collector or manifold immediately after the exhaust valve.

If you have never done it before, make a note of the EGT in straight and level cruise with the wind and waves on the stern then, without changing throttle setting, turn around and put the nose into the weather and see what the temperature is through the maneuver and after steadying back on a reciprocal heading. If you are anywhere near to having load problems you should see a marked increase in EGT.

Watch the EGT while you make a few 360s, see how it changes in response to the increased load. That will tell you how much margin you have as well. I suspect that unless you are very much "overpropped" and/or have a dirty hull and prop, you won't seem much increase while maneuvering.
Thanks Rick. I thought that was true, which is why I haven't worried about it the last 5 years. I can't see any difference in exhaust temperatures regardless of wind or wave conditions and put that down to a 3.71 gear and the flat torque curve of the 3306 Cat. I think the only port for the sensor is on the outlet side which is why it is there, but I'll use a heat gun to measure the TIT. Will that be close to actual?

What prompted this is I have a vibration at 1500 - 1575 rpm on a clean 3 blade wheel and I planned on taking it off this summer and tuning it, and can't decide whether to flatten it as well or not. I doubt it would make the slightest difference to the engine based on your, and others input, but that would be the time to do it. Just can't decide whether I should or not.
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Old 02-10-2013, 11:00 AM   #85
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If the manufacturer doesn't provide a maximum, the best way to set a limit is to load the engine as high as possible - do a bollard pull test for example - and record the highest temperature displayed. That will give you a ballpark for the "top of the green" at least.

There is a standard figure of 900F for 4 stroke normally aspirated diesels that is used by exhaust systems and components manufacturers. This is the one I use:

http://www.asia.donaldson.com/en/exh...ry/1053747.pdf

I have found that the normal operating exhaust temperatures are quite a bit lower. That finding is based on attaching a thermocouple and datalogger on the exhaust elbow or turbocharger outlet where there is usually a convenient port.

Just pulling a figure out of my butt, I would guess your EGT would be between 600 and 700F at maximum load and down to around 200 at no load. Close?

Good timing on that question as I have been doing a lot of work on particulate filter specs for generators so have quite bit of data available. Soot, smoke, and stink are becoming big problems with yachts and we are soon going to be regulated.

(Note to certain other readers: Don't bother to come back with a rant against DPFs installed on road vehicles. I know all about it and really don't care.)
OK, so EGT is one way to deal with the engine overboost question with a cruise prop. Any others? What about calculating/resetting the engine rpm limit based on prop power demand? (cost-benefits aside)

Regarding particulate filters on "yachts", one assumes you are referring to large "regulated" vessels operating in sensitive areas? Care to tell us which organization is developing the standards? What's your prognosis for the recreational ("toy") boating segment?
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Old 02-10-2013, 11:09 AM   #86
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If the manufacturer doesn't provide a maximum, the best way to set a limit is to load the engine as high as possible - do a bollard pull test for example - and record the highest temperature displayed. That will give you a ballpark for the "top of the green" at least.

There is a standard figure of 900F for 4 stroke normally aspirated diesels that is used by exhaust systems and components manufacturers. This is the one I use:

http://www.asia.donaldson.com/en/exh...ry/1053747.pdf

I have found that the normal operating exhaust temperatures are quite a bit lower. That finding is based on attaching a thermocouple and datalogger on the exhaust elbow or turbocharger outlet where there is usually a convenient port.

Just pulling a figure out of my butt, I would guess your EGT would be between 600 and 700F at maximum load and down to around 200 at no load. Close?

Good timing on that question as I have been doing a lot of work on particulate filter specs for generators so have quite bit of data available. Soot, smoke, and stink are becoming big problems with yachts and we are soon going to be regulated.

(Note to certain other readers: Don't bother to come back with a rant against DPFs installed on road vehicles. I know all about it and really don't care.)
That is a very useful document. It doesn't say so explicitly, but this data is referring to outlet temperatures, correct?

If so, from this my Cat 3306TA at 1800 rpm is running about 75 degrees cooler than the chart. I don't know what the accuracy limits of the sensor are, but this would seem to indicate that there is zero problem with the current setup. That, or the gauge is wrong....

Thanks again, Rick. Great information.
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Old 02-10-2013, 11:54 AM   #87
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Regarding particulate filters on "yachts", one assumes you are referring to large "regulated" vessels operating in sensitive areas? Care to tell us which organization is developing the standards? What's your prognosis for the recreational ("toy") boating segment?
There are no regulations currently in effect to monitor the exhaust emissions of yachts, commercial or private.

There are no requirements to meet any particular emissions standard in any area - unless the yacht is burning heavy fuel oil, and there aren't many that do.

The reason we are putting DPFs on yachts is because the paint jobs cost millions, the stink offends owners and guests, and the generators produce oil slicks and little islands of floating soot that stain the waterlines of neighboring yachts as well as the boat that produces them.

I have no doubt that at some point emissions will be controlled, with particulates and NOx being the first to be monitored.
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Old 02-10-2013, 12:00 PM   #88
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Rick wrote;

"I have found that the normal operating exhaust temperatures are quite a bit lower. That finding is based on attaching a thermocouple and datalogger on the exhaust elbow or turbocharger outlet where there is usually a convenient port."

It would seem to me the distance from the closest exhaust valve to the "elbow" would vary considerably and give various results. Dosn't varying the distance from the "fire in the hole" to the pyrometer vary the results? I would think the position of the thermocouple would effect the readings. I put a custom aftermarket SS high rise exhaust on Willy that may have moved the "elbow" 8 or so inches "down the pipe" (up) from where it was. Then there's rate of flow and the diameter of pipes. Dosn't seem to me that EGT readings could be very accurate. Never considered EGT measurements to be very useful. And once you read the results there would be little reason to keep the instrument unless one was over propped.
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Old 02-10-2013, 12:08 PM   #89
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Rick wrote;

And once you read the results there would be little reason to keep the instrument unless one was over propped.
I believe their on-going utility is spotting incipient problems that would show up as changes in normal EGT at a given rpm. I had an Insight cylinder EGT gauge on my airplane and could spot all manner of problems before they became issues. With a single temp point of measurement I suppose all you could notice is a change in typical conditions that would warrant an explanation, but that still seems useful.
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Old 02-10-2013, 12:41 PM   #90
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I believe their on-going utility is spotting incipient problems that would show up as changes in normal EGT at a given rpm.

"And once you read the results there would be little reason to keep the instrument unless one was over propped."

Rick never wrote than and never will!I agree with you that they are very valuable diagnostic and monitoring tools.

It doesn't really matter where the EGT probe is located for our purposes. We are looking for trends, not absolute temperatures. We don't operate within a few degrees of material failure so we don't really care if it is off by a few degrees. Considering most engines don't even offer EGT probe fittings, anything we can get is a plus.
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Old 02-10-2013, 12:50 PM   #91
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It would seem to me the distance from the closest exhaust valve to the "elbow" would vary considerably and give various results. Dosn't varying the distance from the "fire in the hole" to the pyrometer vary the results? I would think the position of the thermocouple would effect the readings. I put a custom aftermarket SS high rise exhaust on Willy that may have moved the "elbow" 8 or so inches "down the pipe" (up) from where it was.
The temperature away from the exhaust valve is hotter than where the manifold connects to the head, particularly on turbocharged engines.

It doesn't matter what the exact temperature is, you just want to know what it is where you are measuring it when the engine is working at maximum load. Once you know what that temperature is you will be able to tell when you have exceeded normal maximum load. You are looking for relative temperatures, changes to the normal, unexpected deviations. Most of us here are not thermodynamicists, you might be but I am not.
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Old 02-10-2013, 01:23 PM   #92
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Just pulling a figure out of my butt, I would guess your EGT would be between 600 and 700F at maximum load and down to around 200 at no load. Close?
I would say so. The "normal" mark from a previous owner is at about the 400-500 degree point and this is where the pointers are at our cruise rpm of approx 1650.
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Old 02-10-2013, 04:18 PM   #93
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"And once you read the results there would be little reason to keep the instrument unless one was over propped."

Rick never wrote than and never will!I agree with you that they are very valuable diagnostic and monitoring tools.

It doesn't really matter where the EGT probe is located for our purposes. We are looking for trends, not absolute temperatures. We don't operate within a few degrees of material failure so we don't really care if it is off by a few degrees. Considering most engines don't even offer EGT probe fittings, anything we can get is a plus.
My bad - I poorly edited Eric's remarks, and he didn't accuse you of saying that. I just deleted part, but not all of his remarks, so my apologies for the confusion....
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Old 02-10-2013, 04:39 PM   #94
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I'm used to using EGT in a plane where it is used to set the mixture. But I use the EGT readings on our boat along with the other instruments to confirm that all is normal with the engines. Should we get something wrapped on a shaft, for exampe, this could put an additional load on the engine and this would be reflected in an increase in EGT.
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Old 02-10-2013, 07:06 PM   #95
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But if you measured the thrust at a reduced rpm like 1500 to 1700rpm I think the larger prop/lower geared boat would loose more (as a percentage) of thrust than the smaller/faster prop boat. The low geared big prop unit at half speed should have less thrust.

The thrust required to move a boat at a set speed does not change because of prop diameter.

Producing the required thrust at slow (under 10K) is always more efficient with the largest diameter that will fit under the boat that it can be geared for..

This assumes the number of blades and blade width is also optimized.

As an example a ride on a tug (HUGE PROP and frequently 6-1 gearing) will show the engine is slowed very little to cut speed while free running .

Going from 10K to 5K does not require half RPM, just far less thrust.

Run a bunch of props thry Skenes to see how Diameter is king of thrust efficiency.
that makes sense. If you were to increase the prop diameter then engine load would increase with a resulting loss of rpm
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Old 02-10-2013, 07:16 PM   #96
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About 850 RPM is my JD's idle speed.
Checked the JD 4045's manual today. Listed idle speed is 750 RPM, but the engine seems more comfortable with 800.
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Old 02-10-2013, 07:27 PM   #97
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It doesn't really matter where the EGT probe is located for our purposes. We are looking for trends, not absolute temperatures. We don't operate within a few degrees of material failure so we don't really care if it is off by a few degrees. Considering most engines don't even offer EGT probe fittings, anything we can get is a plus.
I was following this thread as it drifted into EGTs while I crossed Georgia Strait today. Back in my hotrod Powersmoke days we used to argue ad infinitum about whether pyrometers should be located pre or post-turbo. In our toyboat situation we might be able to generate a meaningful "danger" number for a pre-turbo installation but the vagaries of exhaust routing and plumbing would make a post turbo installation meaningless. And while pre-turbo may generate more repeatable numbers, if the pyrometer goes south it leaves the engine through the turbo.

As Rick points out we don't need an absolute number anyway. Nobody here is pushing the engineering limits for their engines. In the Powersmoke world we were dealing with chipped engines in pickup bodies pulling way bigger loads than Ford ever intended them to pull. In that situation we needed a number where we could back out of the throttle to avoid burning valves. In our business we ran a couple of IHC 466s that were set at 350 HP - that's way too many ponies to take out of that wonderful little engine and our concern there was when to back out of the throttle to avoid melting pistons. I'd hazard to say that - other than idle curiosity - EGTs are meaningless to most users of this forum.
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Old 02-10-2013, 10:32 PM   #98
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I do right on spec at 850. I choose a 2.27:1. In hindsight, I should have chosen the 2.74:1. I was trying to hit a sweet spot at the 1800 rpm mark.
Spy I've thought about it more and concluded that your problem is that of too much power. NT originally had 36hp in the NT26. Then the customers or potential customers took over the designing of the boat and doubled the power. The 30' Willard is a considerably heavier and larger boat w half as much power as your NT so w that information one can't help but think it over powered to go 2 knots. With the 36hp original NT 26 there would be (I suspect) no problem. Since you probably never use the upper speed range you could under prop the boat. You would be at a lower risk of damaging your engine from mis-propping it than the many members here that over prop and the increase of fuel consumption would be very small fly stuff. Yup that would solve your problem w almost no undesirable results. In the process I'd check on where the governor limits the rpm. Should be about 3200. You could even change that to 3000 and operate very close to 3000 w/o danger of overloading. Something to consider.
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Old 02-10-2013, 10:51 PM   #99
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Some NT 26s have 150hp

Don't blame Nordic Tug, blame me. Spy originally had a 42hp BMW (really a 3 cylinder marinized Hatz). After 5000 mostly trolling hours, she was tired. I like having a few extra usable knots and the ability to lift my bow and dig a hole in the stern just like the Bayliners that cruise by the house on the way to and from Desolation all summer long (cheap jab, I know, but still fairly accurate).

I spent oodles of time creating comparative spreadsheets, picking my engine, calculating pitch (thanks Dave Gerr), and installing it. Almost as much fun as using the boat. Next time Spy is on the hard, I'll pitch it down an inch or so (More spread sheets! ). Until then I'll jig.

I actually posed the recommended Volvo Penta 2700-3000 range question to start a discussion about the theoretical WOT rpm, and make some people (like you) a bit uncomfortable.

Thanks for trying to help solve my "problem" though. Cheers.
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Old 02-10-2013, 11:17 PM   #100
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Sounds like a good plan Spy.

Yes I really enjoyed very much spending time going over and over the variables re choosing my re-power engine. Wish I could do it all over again even if I choose the same engine. According to the great psychiatrist Carl Jung we are "P" type personalities. We like things undecided giving us options.

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