Why do folks over prop

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psneeld, your quote is right to the point...


""A diesel is overloaded when the load imposed limits the rpm demanded by the governor. This is seen as the point where the governor calls for more fuel delivery but the [engine] speed can not increase" [my addition]


Backing off on the throttle of an engine that is NOT over-propped will generally allow the engine to operate below its max rated power curve which will, as long as it operates within the right temperature range, help prolong its MTBO. But using the prop load to limit the engine to that same RPM will do exactly the opposite. And if you run at that load-limited RPM continuously, you will be running at or above max rated load 100% of the time. I can't for the life of me understand why someone would intentionally do that.
 
psneeld said:
Ok....but a huge number here are not under engine warranty and know better than rookie info.


If you don't want to overprop, your choice.


If you do want to overprop for reasons discussed, fine if you know the dangers...not the usual drivel spouted by amatuers.


Read the second sentence of para 3 in post 30.
Click to expand...



Why don’t you have the courage and honor to just call me out directly?

I think we both know why.
 
ghost said:
Why don’t you have the courage and honor to just call me out directly?

I think we both know why.
Click to expand...
Wasn't thinking particularly if you in general, could care less...but as the old expression says. .. if you think the words apply to you.....


Well actually, your partial post IS discussed by another poster as "no one is saying" .....and I pointed them in that direction. Post #57.


You want honor and courage...I have plenty to back me up and you don't have a clue about who I am..... Let it go. Every day TF is just a round robin where readers have to guess who actually knows anything.....and when those posts are challenged.
 
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psneeld wrote;
“and you don't have a clue about who I am..... Let it go.”
You show us every day who you are. Ghost and all the rest of us know who you are.
 
Nomad Willy said:
psneeld wrote;
“and you don't have a clue about who I am..... Let it go.”
You show us every day who you are. Ghost and all the rest of us know who you are.
Click to expand...
You really think forum posts make the whole person?


There is good info on this thread, let's not get it shut down because it's becoming personal.
 
I will let others decide what they want to believe.


Believe me, if I thought an apology was warranted I would post it...I have before.
 
Engineers get in a bar fight over engine loading curves....
 
I think we should shut down any thread where everyone is not welcome to post. Calling people amateurs should get you booted immediately.


Moderators?


Moderators?


<crickets>
 
syjos,
We all advertise who we are by what we say, to whom and our use of words ect ect. Guys like me who basically let it all hang out are better known but of those that post quite a bit and often are quite well known. Sometimes I’ll be reading a post and try to guess who the poster is. And we can leave well known trails. If a new post starts out with quarter beam buttock lines more than dozens will know who the poster is. What we post comes out of our brains (consider the source they say) and who we are is mostly what’s in our brains.

psneeld says “I will let others decide what they want to believe.”
Hmmm we all know him well enough to know that’s farthest from the truth. But parts of hundreds of posts show that he essentially says that. Wants us to believe it I suppose. But the vast majority of us are trying to get others to believe what we believe. Or at least think about what we are thinking about.
 
ghost said:
I think we should shut down any thread where everyone is not welcome to post. Calling people amateurs should get you booted immediately.


Moderators?


Moderators?


<crickets>
Click to expand...

Why shut down the thread? It’s not the thread that is the problem. And that’s what we’re here for is threads and conversation.
 
Unless its something specific like a part number , most folks post their OPINION.

Frequently based on decades of boating , but still simply, their opinion.

Good , bad or insane is for the reader to decide.

With multiple responses most really strange concepts are weaned out rapidly..
 
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My thread, my call. Please don't bring machismo issues into a thread about over propping. I can guarantee you most don't care about how many posts you have, how large your d... is, how bright or dumb you are, how brave you are, or how wise or not you are.

Most of us are looking to improve our knowledge, some one's bravery (or questioning it) does not add to that. I posted this thread because I genuinely didn't know why people over prop. I did not post this thread to learn about how many posts some one has, I too can look under your name for that, or how brave some one is, generally not a requirement for trawler cruising, though that might make an interesting thread - when did bravery enter your cruising experience? I'm sure it would get at least two posts.

I was a moderator in one of my many interests and it has always fascinated and depressed me at the same time - no hope for humanity - how insignificant an issue could bring grown men to thump their chest and bring general emotional pollution to a thread.
 
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rsn48 said:
I run into this frequently with boaters, they brag about how their boat is over propped not realizing the damage that can be done to a motor that functions at lower RPM pushing more weight.

So why do people over prop?
Click to expand...

"So why do people over prop?"
A vast majority over prop because they have no idea about the reason for propping correctly and/or the affects and repercussions that over propping can bring. I am sure there are many other reasons but this would be the most common by far.
 
"This has been beat to death for 100 years. It is not rocket science guys" flg

This has strayed so far off the subject it should have been answered a week ago. OH YES it was answered. :banghead:


 
when I bought my boat it was over propped by 6 inches of propeller pitch. I replaced the props with the correct ones and was able to achieve the rated engine RPM. Running my at trawler speed. which is where I am most comfortable oh, my engine will not achieve (well what I think is sufficient temperature) so now I see the value of being over propped. I never attempt to run my boat act maximum rpm and speed. Honestly it is loud and not comfortable for me
 
So why do people over prop?"

Because it works.
For the knowledgeable owner / operator with an understanding of the limiting parameters, it can reduce RPM, noise, and slightly improve fuel consumption without effecting engine life expectancy.

Now if you don't know what your doing, it can cost you dearly. But that's true of most things in boating.

Ted
 
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Nomad Willy said:
Probably most that are overpropped are because the boat came that way.

Then when they haul out and perhaps think about prop load they notice many here on TF are overpropped and most seem experienced or even old salts. Then they recall hearing one will burn less fuel and of course the’ve had the experience of going to the fuel float (of barge) and getting shocked at the cost. And that’s it. They just keep on keep’in on thereafter.

Then a few come along every now and then w a bunch of numbers and theories that are very overwhelming and it’s rejected because even the experts on TF continue to argue about whether it’s good or bad. Then they think of fuel again. So the motive to change is very small so they chime in w the others claiming it’s the smart thing to do. So if it’s the smart thing to do it would be dumb to do any different and they get to talk about how smart it is to do w the big boys on TF too. And it goes on and on.

But another thing goes on and on. That’s the fact that no engine manufacturer recommends overpropping.
Then there’s hull speed. All the old salts talk about hull speed. So many attempt to or do run their boat at hull speed. May be the perfect speed for SD boats not close to FD but for those close to hull speed it’s not the speed to go. And for FD it’s the speed to never ever go unless the boat is overpowered (most are) and you’re doing a spring check on systems engine wise.

But if you’re at all concerned about fuel consumption most SD and all FD boats should be run 1/2 to one knot below hull speed. But the average TF guy is confused again and hears many run at a “sweet spot” and then we have license to find a speed he feels is nice. Almost always the speed that is run at the rpm where there is the least vibration and hence noise as well and almost absolutely everybody like that. Hard not to like smooth and relatively quiet. And the old salts on TF are frequently talk’in about it so it must be the thing to do.

But re overpropping is not recommended by any engine manufacturer.
Click to expand...

This is my post on page two and one of the big reasons many overprop.
You could say it’s cool. When the subject is brought up the newbies are overwhelmed w theories and numbers. And they see many old salts on the forum do it. So many just do it because it makes them look good ... like they understand it and are in the know. More of a copy cat thing than anything else. But saving fuel gets a lot of attention. I think it’s usually 3-5% but one chap here speaks of 10%. ??
 
Yes, this subject has been beaten to death. However, there are some of us (me) who are a bit slow. I learn a lot by reading what more knowledgeable folks have to say on the topic. In this thread, I have learned more about how diesel engines work, their power output, and how that relates to the loads imposed by a prop. It takes me an inordinate amount of time to learn some concepts so the back and forth discussion is helpful.



Sure there are times when folks may get a bit too emotionally involved in the discussion, but that is easily handled by de-escalation.
 
Thanks Dave for your non-combative, objective and good natured posting.
 
Nomad Willy said:
This is my post on page two and one of the big reasons many overprop.
You could say it’s cool. When the subject is brought up the newbies are overwhelmed w theories and numbers. And they see many old salts on the forum do it. So many just do it because it makes them look good ... like they understand it and are in the know. More of a copy cat thing than anything else. But saving fuel gets a lot of attention. I think it’s usually 3-5% but one chap here speaks of 10%. ??
Click to expand...
Eric, I'm just curious how you deduce that people think it's cool or its a copy cat thing? Curious if you you asked people why they did it, or maybe took a poll?

Think you will find most here who did it found what they perceived is a positive effect.

There is a guy on this forum who butchers anchors. He is in pursuit of better performance. There is no anchor manufacturer that condones what he does. Does he do it because it's cool or he's just copycating somebody else? Sound familiar?

Ted
 
Over-propping seems wrong to me. Simply because it isn't proper. Simple as that. Like one wants to outsmart your boat's dsigner/builtder? :D
 
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O C Diver said:
So why do people over prop?"

Because it works.
For the knowledgeable owner / operator with an understanding of the limiting parameters, it can reduce RPM, noise, and slightly improve fuel consumption without effecting engine life expectancy.

Now if you don't know what your doing, it can cost you dearly. But that's true of most things in boating.

Ted
Click to expand...


Your answer is accurate but only when it applies to hull speeds with specific boats and power plants and when operated by a knowledgeable owner.
 
Maybe a picture will help....


This is from a Deere 4045 spec sheet, but is typical of all diesels driving props.


The red line shows the engine's max power capability at each RPM. This is the power the engine is capable of producing, but how much it actually produces depends on the load. Asking the engine to produce power anywhere above the red line creates an overload condition.


The gray line is the load required to spin a boat prop. It has a different shape than the engine output curve, starting out low, then progressively climbing as RPMs increase. Looking at it, you can see how much more power is required for relatively small increments in RPM (and speed) - something most of us know through experience.



The gray line represents a "correctly" matched prop. The key is that the prop load meets, but never exceeds the power output of the engine. Because of the difference in the shapes of the curves, the match between load and available power only occurs at max RPM.


When people look at over propping, they are looking at the space in the graph between the gray and red lines. That space represents power that the engine could produce without being overloaded, but the prop can't provide the load. Over propping relocates the prop load curve to tap more of the available power at lower rpms.


The orange crayon line draw by a child (me) shows an example of an over propped load. The load from the bigger prop grows faster as rpms increase, and utilizes more available engine power at lower rpms. You get the same power as the "correct" prop, but at lower RPMs so your engine is presumably quieter, and maybe operating at better fuel efficiency. That's what people are after when over propping.


But you can also see that now the orange line over-takes the engines max power curve shown in red. If you give the engine more throttle trying to push to higher rpms, you are now over loading the engine. That's the danger in over propping. If you are propped such that it's possible to overload like this, engine manufacturers will void your warranty. That only matters on a new engine with a warranty, but it also speaks to the hazards involved.


Proponents of over propping say to just not push past the overload point. If it hurts, don't do it. It has also been noted that exhaust gas temp (EGT) is an indication of when you are crossing over the red line, so instrumenting for that and keeping operation below max allowed EGT is a way to stay below the red line.



Hope this helps.
 

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twistedtree said:
Maybe a picture will help....


This is from a Deere 4045 spec sheet, but is typical of all diesels driving props.


The red line shows the engine's max power capability at each RPM. This is the power the engine is capable of producing, but how much it actually produces depends on the load. Asking the engine to produce power anywhere above the red line creates an overload condition.


The gray line is the load required to spin a boat prop. It has a different shape than the engine output curve, starting out low, then progressively climbing as RPMs increase. Looking at it, you can see how much more power is required for relatively small increments in RPM (and speed) - something most of us know through experience.



The gray line represents a "correctly" matched prop. The key is that the prop load meets, but never exceeds the power output of the engine. Because of the difference in the shapes of the curves, the match between load and available power only occurs at max RPM.


When people look at over propping, they are looking at the space in the graph between the gray and red lines. That space represents power that the engine could produce without being overloaded, but the prop can't provide the load. Over propping relocates the prop load curve to tap more of the available power at lower rpms.


The orange crayon line draw by a child (me) shows an example of an over propped load. The load from the bigger prop grows faster as rpms increase, and utilizes more available engine power at lower rpms. You get the same power as the "correct" prop, but at lower RPMs so your engine is presumably quieter, and maybe operating at better fuel efficiency. That's what people are after when over propping.


But you can also see that now the orange line over-takes the engines max power curve shown in red. If you give the engine more throttle trying to push to higher rpms, you are now over loading the engine. That's the danger in over propping. If you are propped such that it's possible to overload like this, engine manufacturers will void your warranty. That only matters on a new engine with a warranty, but it also speaks to the hazards involved.


Proponents of over propping say to just not push past the overload point. If it hurts, don't do it. It has also been noted that exhaust gas temp (EGT) is an indication of when you are crossing over the red line, so instrumenting for that and keeping operation below max allowed EGT is a way to stay below the red line.



Hope this helps.
Click to expand...

Thank you - great post
 
Ted writes;
“Eric, I'm just curious how you deduce that people think it's cool or its a copy cat thing? Curious if you you asked people why they did it, or maybe took a poll?”

That’s how things become cool. A cool guy does it, wears it, says it ect ect.
I’m overpropping like the gurus on TF. Burn less fuel, make less noise but most importantly it’s cool because the gurus do it.
Like Mark says “Like one wants to outsmart your boat's dsigner/builtder?” these overproppers are so smart they know more than the designers.
Out smarting is high level coolness.

I offer no credentials or relative footnotes for the above. It’s cool enough not to need any objectivity.
 
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smitty477 said:
Your answer is accurate but only when it applies to hull speeds with specific boats and power plants and when operated by a knowledgeable owner.
Click to expand...

Or someone that knows at what rpm overloading begins and never ever goes there. But where is that? 95% of overproppers probably don’t have any idea. But most all that do it are in the know and are .. cool. And how cool is that?

Mr. TTree is spot on of course. Thanks TT for finally solving the overpropping issue. But how many actually understand it? Better go through it again to make sure I got it. I’m sure I did but ...

The actual solution to the problem is to get a smaller engine. Not a cost effective solution unfortunately.
 
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markpierce said:
Over-propping seems wrong to me. Simply because it isn't proper. Simple as that. Like one wants to outsmart your boat's dsigner/builtder? :D
Click to expand...
The above quote is good enough for me. I want to spend my time enjoying the boat, not trying to outsmart the engineers who built the engines.:blush:
 
Nomad Willy said:
Ted writes;
“Eric, I'm just curious how you deduce that people think it's cool or its a copy cat thing? Curious if you you asked people why they did it, or maybe took a poll?”

That’s how things become cool. A cool guy does it, wears it, says it ect ect.
I’m overpropping like the gurus on TF. Burn less fuel, make less noise but most importantly it’s cool because the gurus do it.
Like Mark says “Like one wants to outsmart your boat's dsigner/builtder?” these overproppers are so smart they know more than the designers.
Out smarting is high level coolness.

I offer no credentials or relative footnotes for the above. It’s cool enough not to need any objectivity.
Click to expand...

I agree that new and low information boaters copy others in order to be cool in a salty, nautical way. Overpropping is just one example.

I've ranted about this in another post but one thing that irritates the heck out of me is boaters that unnecessarily announce themselves through Dodd Narrows. New boaters hear others announcing themselves and think it's the cool nautical thing. It gets worse every year.

The othe irritating thing is turning on the anchor light at designated anchoring areas. We just spent 5 days at Reid Harbor and everybody had their anchor lights on. It was so bright that the harbor looked like a parking lot. Light pollution was so bad that we could not see the stars through the hatch in the stateroom. It never used to be like this 10 to 20 years ago. We are currently anchored in Montague and we are almost the only boat with the anchor light off. The other boaters think that having the anchor lights on is the cool salty thing to do?
 
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syjos wrote;
“I've ranted about this in another post but one thing that irritates the heck out of me is boaters that unnecessarily announce themselves through Dodd Narrows. New boaters hear others announcing themselves and think it's the cool nautical thing. It gets worse every year.”

Totally agree. No need. And then some think “over” is a substitute for a period on the radio.

Anchor lights like at Montague Harbour? Who cares? It’s beautiful. I turn mine on.
 
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