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post #71 of 86 Old 07-31-2013
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Re: Conversion to oil as coolant?

Mark has brought up a good point in the idea that there IS some "coasting" or inertial effect on a boat's prop. Is this actually a significant factor? If so, I wonder what that factor may be. I picture a prop as having constant pounds of torque at any constant RPM, regardless of what's going on with the hull but as the hull experiences slight accelerations and decelerations in its path through the water, turning at that constant RPM, does the torque vary to a significant amount? Water speed past the prop certainly has effect as we can all attest to as the prop hums in neutral under sail alone.

Alberg 35: With a philosophical flourish Cato throws himself upon his sword; I quietly take to the ship.
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Re: Conversion to oil as coolant?

Yea, just proves a statement my wife was told many many years ago by her grandfather and she has repeated a thousand times since when appropriate... "There never has been any shortage of either a**es or fools and it not likely there ever will be". I think the man had it figured out wouldn't you say? I am the OP and I am now done with this thread.
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Re: Conversion to oil as coolant?

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Mark has brought up a good point in the idea that there IS some "coasting" or inertial effect on a boat's prop.
A miniscule amount which is offset by drag almost instantly on props our size.


Quote:
Is this actually a significant factor? If so, I wonder what that factor may be.
No, Tiny


Quote:
I picture a prop as having constant pounds of torque at any constant RPM, regardless of what's going on with the hull but as the hull experiences slight accelerations and decelerations in its path through the water, turning at that constant RPM, does the torque vary to a significant amount?
Next to nothing unless its a drastic reduction on the hull's speed... still next to nothing really at our hull speeds and props.

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Water speed past the prop certainly has effect as we can all attest to as the prop hums in neutral under sail alone.
Next to nothing at our hull speeds. Its usually included in the prop's design to be minimized.
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post #74 of 86 Old 07-31-2013
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Re: Conversion to oil as coolant?

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Originally Posted by mark2gmtrans View Post
Actually you should factor in 28 years of diesel repair and maintenance, as well as quite a few manufacturers classes and training seminars. You might also factor in PHYSICS, and the fact that you must not have ever taken apart a fuel pump or governor. In fact you might also factor in the part where you simply do not understand diesel engines at all, cannot seem to read plain English, understand a good explanation, or admit that you are wrong.

And to bljones, your analogy is right on, your interpretation is incorrect. Tell me what would happen to your weightlifter if he put 350 pounds of lift on a 10 ounce weight? He would rip his own shoulder out of socket with the excess force applied to something that did not need it, or he would toss the bloody thing across the room.

The metering system does not put the same amount of fuel into the injector all the time, even at the same RPM. HOW MANY TIMES MUST THIS FACT BE STATED BEFORE SOME OF THE MORE DENSE STUDENTS IN THE CLASS UNDERSTAND IT? You have a governor, and fuel pump which vary the rail pressure under a load, I cannot explain this to you if you insist that what you think you know is correct over what is actually happening.
Eaaaasy there Tex - you'll blow a gasket. (You do know what gaskets are don't you?). I realize it won't have crossed your mind but there are people on this thread that have been working on gas & diesel engines in boats & cars longer than you have been alive. Some of us actually know a few things - like the fact that large numbers of small diesel marine engines are only governed by the skippers hand on the throttle handle.

I yanked and stripped my first Studebaker (look it up) V8 before you were born.

You are putting up so many tiny little trees that you don't seem to even have a concept of the forest. Diesel engines in boats are loaded and as close to steady state as anything this side of a stationary engine - saying they "coast" to any significant degree indicates little knowledge of how boats, particularly sailboats (which this forum is about) operate in the real world.

Once away from the dock they are set at the usual running RPM for that boat/prop combo and left there until something changes like the end of the voyage. They do NOT vary the way road engines do. I don't care how many pressure pumps you have rebuilt - THAT is the way they operate in the marine environment - under steady load, not coasting or varying their output.

One last thing before you go on ignore;
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I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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post #75 of 86 Old 07-31-2013
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Re: Conversion to oil as coolant?

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Originally Posted by dem45133 View Post
Mark... maybe your just an a**. You are thinking in terms of minutia when we have been talking in general terms.Dave
No "maybe" about it. I think he needs to increase his Prozac dosage - or remember to take it every morning.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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Re: Conversion to oil as coolant?

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Wow!!, this is becoming a "Bent" thread. Paul T
Not the same at all - Brent is simply a missionary for what he considers the safest & cheapest method of building an offshore sailboat.

Tex here is a run of the mill, know it all a$$hole.

HUUUUGE difference.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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Re: Conversion to oil as coolant?

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Originally Posted by smurphny View Post
Mark has brought up a good point in the idea that there IS some "coasting" or inertial effect on a boat's prop. Is this actually a significant factor? If so, I wonder what that factor may be. I picture a prop as having constant pounds of torque at any constant RPM, regardless of what's going on with the hull but as the hull experiences slight accelerations and decelerations in its path through the water, turning at that constant RPM, does the torque vary to a significant amount? Water speed past the prop certainly has effect as we can all attest to as the prop hums in neutral under sail alone.
Of course there are minor variations - there are variations from blade to blade on the prop as it swings. There will be variations between a boat going into a wave VS going over the top & down the back side.

The variations are insignificant, particularly in the context that is under discussion here - a sailboat motoring at a steady state VS road usage in a wheeled vehicle.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.

Last edited by SloopJonB; 07-31-2013 at 07:42 PM.
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post #78 of 86 Old 07-31-2013
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Re: Conversion to oil as coolant?

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Originally Posted by SloopJonB View Post
Of course there are minor variations - there are variations from blade to blade on the prop as it swings. There will be variations between a boat going into a wave VS going over the top & down the back side.

The variations are insignificant, particularly in the context that is under discussion here - a sailboat motoring at a steady state VS road usage in a wheeled vehicle.
Yes, it has always been my understanding that a marine diesel is essentially an industrial motor, designed specifically to run at a continuous torque for extended periods of time. The journals and block structure are relatively massive for the amount of power produced. I just wondered about the actual amount of differential in torque produced by gaining and losing speed with each wave. I would guess considerably <1%. This could easily get into flute music which makes my head hurt.
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post #79 of 86 Old 07-31-2013
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Re: Conversion to oil as coolant?

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Originally Posted by mark2gmtrans View Post

Tell me what would happen to your weightlifter if he put 350 pounds of lift on a 10 ounce weight? He would rip his own shoulder out of socket with the excess force applied to something that did not need it, or he would toss the bloody thing across the room.

.
Again....
No.

Potential power, ie Gross torque, is not fully realized power. if the torque exceeds needs the excess torque is bled off...


that is what makes brakestands look so impressive, and in reverse, why diesel engines blow black smoke when plowing through heavy seas- the available torque produced by the engine is overwhelmed by the forces (wind, waves, current) working against it.



Seriously, you think a weightlifter will blow out his shoulder by lifting a 10 oz. weight?
Nope- the excess force is always expended to the objective least resistive. Newton.


Being a mechanic for 28 years on the internet doesn't make you an engineer for one month in real life, son.


Don't claim what you don't know.

It's 5 o'clock somewhere:


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Last edited by bljones; 08-01-2013 at 12:00 AM.
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post #80 of 86 Old 08-01-2013
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Re: Conversion to oil as coolant?

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Originally Posted by SloopJonB View Post
Not the same at all - Brent is simply a missionary for what he considers the safest & cheapest method of building an offshore sailboat.

Tex here is a run of the mill, know it all a$$hole.

HUUUUGE difference.
Sloop,

I meant "Bent", like in "Bent Sailor", the person in Australia, whose posts can be very long, full of many unrelated details, phrases that I can't understand, and almost always wrong.

He is, however, polite and respectful, to me, anyway.

Paul T
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