Fuel Mixture and Load

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
SeaHorse II said:
:) I would have bet good money on that being the reason you want to go slower. Have you looked into getting a trolling valve? Have you tried lowering your idle to 650-700 rpm? That just might put you at 2.5 knots which is a speed I've caught a lot of salmon at.
Click to expand...

No trolling valve available. I have a mechanical box. The hydraulic box only came with an 8· down angle on the output shaft.
 
:)Getting back to the original post and comments by some that the govener controls engine speed , sorry but you are confusing a diesel engine to a gas craftsman lawnmower.the govener controls the amount of fuel injectected , the speed of the engine relative to the fuel injected is controled by the load, think of a pickup diesel engine as you go up the hill you still need to depress the accelerator pedal to overcome the additional load of the hill.hope that helps.
 
SeaHorse II said:
I just kick it in & out of gear when in the marina. 850 does seem a tad high, though.
Click to expand...

Yeah, in gear when making turns in the marina, and out of gear on the straight-of-ways when needed to reduce speed.

About 850 RPM is my JD's idle speed. At about 1000 it generates half its horsepower and pushes the Coot about half its 7+ knot maximum speed.
 
Last edited:
Mark,
About 1000rpm at full throttle but you can't go 1000rpm at full throttle.
 
manyboats said:
Mark,
About 1000rpm at full throttle but you can't go 1000rpm at full throttle.
Click to expand...

Huh??? At full throttle (2400 RPM), the Coot slightly exceeds hull-speed, about 7.4 knots. Here we're moving at 6.3 knots at 1800 RPM (68 out of a maximum 80 horsepower):

avatar1295_48.gif
 
Last edited:
Our FL120s idle at about 600 rpm. With our now-pitched-down props this gives us an idle speed of about 3.5 knots. This is slow enough that there is no need shift in and out of gear. We carry this speed right up to the turn into our slip.

We learned a long time ago that too litle speed is worse than too much speed. We retain good rudder authority all the way into the slip and this combined with the ability to vary the thrust between the props make for very precise boat control all the wy through the maneuver. Plus it makes it much harder for the wind or current to take control of the boat.
 
Last edited:
I much prefer approaching my berth at about one knot or less. Don't want to go faster than I'd want to hit the dock. Since my minimum in-gear speed is also about 3.5 knots, I'm often in neutral approaching the dock.
 
I think gear ratios and the motor they are attached to make a big difference in idle speed. My volvos top out at 3600 rpm and at idle of 600 i am turning my pops at 16% of their max rpm. The guy next door with the cummins that tops out at 2600 and idles at 600 is turning his props at 23% of full while crusing through the harbor. When i put my boat in gear at idle there is a gentle swirl of water out the back and it slowly get to just under 3 knt. The neighbor with the cummins put his boat in gear and there is a larg rush of water out the back off he goes, in and out of gear to keep it slowed down 16% Vs 23% is a sizable difference. It is the RPM range of the motor thar really makes the difference and also drives us to use different ratios.
 
expat said:
:)Getting back to the original post and comments by some that the govener controls engine speed , sorry but you are confusing a diesel engine to a gas craftsman lawnmower.
Click to expand...

Sorry but your explanation is oversimplified, like the lawnmower. If we take that explanation to its end, your example engine is controlled by ankle rotation in response to inner ear and visual inputs.

There are as many control schemes as there are applications.

Limiting-speed governors control the idle and maximum speed settings
of the engine. The intermediate range is controlled by the position of
the throttle linkage.

Variable-speed governors that are designed to control the speed of
the engine of the throttle setting.

Constant-speed governors maintain the engine at a single speed
from no load to full load.

Load limiting, to limit the load applied to the engine at any given
speed to prevent overloading the engine at whatever speed it may be running.

Load-control, used for adjusting to the amount of load applied at the
engine to suit the speed it is set to run.

Pressure regulating, used on an engine driving a pump to maintain a constant inlet or outlet pressure on the pump.
 
RickB said:
Sorry but your explanation is oversimplified, like the lawnmower. If we take that explanation to its end, your example engine is controlled by ankle rotation in response to inner ear and visual inputs.

There are as many control schemes as there are applications.

Limiting-speed governors control the idle and maximum speed settings
of the engine. The intermediate range is controlled by the position of
the throttle linkage.

Variable-speed governors that are designed to control the speed of
the engine of the throttle setting.

Constant-speed governors maintain the engine at a single speed
from no load to full load.

Load limiting, to limit the load applied to the engine at any given
speed to prevent overloading the engine at whatever speed it may be running.

Load-control, used for adjusting to the amount of load applied at the
engine to suit the speed it is set to run.

Pressure regulating, used on an engine driving a pump to maintain a constant inlet or outlet pressure on the pump.
Click to expand...

Great summation Rick. For those who seek the cruising prop route, are there any governors that could be retrofitted (at great expense most likley) to existing engines?
 
RickB said:
It is not a toy boat surveyor's job to approve or disapprove anything on your boat. He should keep his opinions to himself unless you ask, otherwise his role is to document condition so far as can be determined by visual examination. Period.

Unless the surveyor is representing a class society and is conducting a survey related to the vessel's classification or statutory status he has no mandate to bless or condemn anything.
Click to expand...
Rick, on a related question, would adverse effects of over propping be evident in elevated EGT when running at lower cruising rpms? Put another way, is it possible to experience adverse effects w/o an increase in EGT? Delfin is slightly overpropped and runs at around 475 degrees at cruising rpm with the sensor downstream of the turbo in the dump tube (I think). Not sure it's relevant, but the max EGT is 875 degrees at 90% of rated rpm, which is all I can get with the current pitch.

Thanks...
 
Third-Reef,
Good and very applicable point and over propping just narrows the range.
 
sunchaser said:
Great summation Rick. For those who seek the cruising prop route, are there any governors that could be retrofitted (at great expense most likley) to existing engines?
Click to expand...

Set screw on throttle linkage....
 
markpierce said:
About 850 RPM is my JD's idle speed. QUOTE]

If i'm not mistaken the book idle speed for the JD 4045 is 650 RPM. 850 sounds high, for any diesel. The higher the idle speed the greater the chance for transmisson wear as you slip in and out of gear.
Click to expand...
 
sunchaser said:
markpierce said:
About 850 RPM is my JD's idle speed. QUOTE]

If i'm not mistaken the book idle speed for the JD 4045 is 650 RPM. 850 sounds high, for any diesel. The higher the idle speed the greater the chance for transmisson wear as you slip in and out of gear.
Click to expand...

I just looked this engine up and this is what the jd manual says. But I think the 850 is in neutral with no load

IDLING ENGINE​
Avoid unnecessary engine idling. Prolonged idling may
cause the engine coolant temperature to fall below its
normal range. This, in turn, causes crankcase oil dilution,
due to incomplete fuel combustion, and permits formation
of gummy deposits on valves, pistons, and piston rings.
It also promotes rapid accumulation of engine sludge
and unburned fuel in the exhaust system.
Slow idle speed for this engine is 800—850 rpm at
factory. If engine must be left running more than 3 or 4
minutes, minimum engine speed should be 1200 rpm.
DO NOT allow engine to idle longer than 5 minutes.​
NOTE: Generator set applications where the governor is
locked at a specified speed may not have a slow
idle function. These engines will idle at no load
governed speed (high idle).​
S11
http://www.google.com/url?sa=t&rct=...PwAHB18thF2jVaH5g&sig2=_OHkqDuhG_dEXlVbPaLzQQ
Click to expand...
 
Hmmmm...650...850...anyone oiut there that actually OWNs a JD care to share????:socool::D:rofl:
 
sunchaser said:
markpierce said:
About 850 RPM is my JD's idle speed. QUOTE]

If i'm not mistaken the book idle speed for the JD 4045 is 650 RPM. 850 sounds high, for any diesel. The higher the idle speed the greater the chance for transmisson wear as you slip in and out of gear.
Click to expand...

It's likely my memory is lacking. But the engine seems happier at 800 or so.
Click to expand...
 
Delfin said:
Rick, on a related question, would adverse effects of over propping be evident in elevated EGT when running at lower cruising rpms? Put another way, is it possible to experience adverse effects w/o an increase in EGT?
Click to expand...

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.
 
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.
 
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.
 
Marin said:
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.
Click to expand...

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/exhaust/support/datalibrary/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.)
 
RickB said:
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.
Click to expand...
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.
 
RickB said:
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/exhaust/support/datalibrary/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.)
Click to expand...

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?
 
RickB said:
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/exhaust/support/datalibrary/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.)
Click to expand...
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.
 
skidgear said:
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?
Click to expand...

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.
 
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.
 
manyboats said:
Rick wrote;

And once you read the results there would be little reason to keep the instrument unless one was over propped.
Click to expand...
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.
 
Delfin said:
I believe their on-going utility is spotting incipient problems that would show up as changes in normal EGT at a given rpm.
Click to expand...


"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.
 
You must log in or register to reply here.

Similar threads

V
Diesel in my fuel injection pump
2
Replies
44
Views
3K
jgtrucking
jgtrucking
socalrider
Possible Lehman 120 injector pump rebuild in San Diego?
Replies
16
Views
1K
GrandWood
G
P
FL135 question
Replies
6
Views
491
BruceK
BruceK
Pau Hana
Generator woes- low compression across all cylinders
Replies
23
Views
3K
Symphony
Symphony
Max Simmons
Fuel Leak Solved!
Replies
5
Views
473
Endeavor GB 32
Endeavor GB 32

Latest posts

Back
Top Bottom