Useless propeller
 

"Paladin" noneofyourbusiness.www wrote in message
...

"Gilligan" wrote in message
. ..
|
| "Paladin" noneofyourbusiness.www wrote in message
| ...
|
| "Gilligan" wrote in message
| . ..
| |
| | http://encarta.msn.com/media_4615415...for_Water.html
| |
| |
| |
|
| The diagram proves my point. Since there is no significant temperature
| change involved with a propeller but there is a significant pressure
| change
| then the water does not vaporize because it boils. Rather it vaporizes
| because
| of the pressure change.
|
| I'm just so brilliant. You can't even manage to misdirect me.
|
|
| I can't misdirect you, but I can set you straight.

You've done an inadequate job of it so far...

| When water boils, as in your kettle, those "bubbles" are water vapor
| suspended in the liquid water.

Agreed. But, suspended is a poor word choice. I prefer to call it
water vapor displacing the liquid water.

| Cavitation is caused by the propeller slipping on water vapor suspended
in
| the liquid water.

Quaintly envisioned. Highly inadequate. Cavitation is a descriptive term
used
to describe the vaporization of the water near the low pressure side of
the
propeller blades resulting in over-revving of the engine. The over-revving
of
the engine is caused by the prop losing contact with the water.


| Would it then be reasonable to say that cavitation is caused by water
| boiling?

Not in the case of a boat unless it was in a giant pot of boiling water
on the stove.

| OR
|
| Cavitation can only happen in your tea kettle?

Cavitation could very well be caused by operating a prop in boiling
water but the prop doesn't cause the water to boil. The fire under
the tea kettle is doing that job.

Now, who's straightening out whom?

Suppose I have water in a beaker and place it in a bell jar. The air in the
bell jar is pumped out, lowering the pressure. Eventually the water begins
to boil.

Where is the heat source causing it to boil?

Useless propeller
 

OK Group,

What happened to the original statement; "Useless propeller" Let's get
back to that! Why is a Two Blade Folding Prop a Useless propeller and a
Four Blade fixed going to work better in rough, choppy sea?




http://community.webtv.net/tassail/ThomPage

Useless propeller
 

"Gilligan" wrote in message ...
|
| "Paladin" noneofyourbusiness.www wrote in message
| ...
|
| "Gilligan" wrote in message
| . ..
| |
| | "Paladin" noneofyourbusiness.www wrote in message
| | ...
| |
| | "Gilligan" wrote in message
| | . ..
| | |
| | | http://encarta.msn.com/media_4615415...for_Water.html
| | |
| | |
| | |
| |
| | The diagram proves my point. Since there is no significant temperature
| | change involved with a propeller but there is a significant pressure
| | change
| | then the water does not vaporize because it boils. Rather it vaporizes
| | because
| | of the pressure change.
| |
| | I'm just so brilliant. You can't even manage to misdirect me.
| |
| |
| | I can't misdirect you, but I can set you straight.
|
| You've done an inadequate job of it so far...
|
| | When water boils, as in your kettle, those "bubbles" are water vapor
| | suspended in the liquid water.
|
| Agreed. But, suspended is a poor word choice. I prefer to call it
| water vapor displacing the liquid water.
|
| | Cavitation is caused by the propeller slipping on water vapor suspended
| in
| | the liquid water.
|
| Quaintly envisioned. Highly inadequate. Cavitation is a descriptive term
| used
| to describe the vaporization of the water near the low pressure side of
| the
| propeller blades resulting in over-revving of the engine. The over-revving
| of
| the engine is caused by the prop losing contact with the water.
|
|
| | Would it then be reasonable to say that cavitation is caused by water
| | boiling?
|
| Not in the case of a boat unless it was in a giant pot of boiling water
| on the stove.
|
| | OR
| |
| | Cavitation can only happen in your tea kettle?
|
| Cavitation could very well be caused by operating a prop in boiling
| water but the prop doesn't cause the water to boil. The fire under
| the tea kettle is doing that job.
|
| Now, who's straightening out whom?
|
| Suppose I have water in a beaker and place it in a bell jar. The air in the
| bell jar is pumped out, lowering the pressure. Eventually the water begins
| to boil.
|
| Where is the heat source causing it to boil?

There is no heat source in that case but the water
is not boiling.

Go to a dictionary and look up the definition of boil.
You will note that it mentions application of heat.

Lowering pressure does not add heat. Therefore, to
use the word boil is incorrect to describe the bubbling
action lowering the pressure causes.

Water plus heat = boil
Water minus pressure = vaporization

Your thinking is sound; it's your use of the verb 'boil'
that's faulty and it muddles the issue. People like
Old Tom quickly get lost. (or should I say "more lost?")

Get it?


Paladin

--
Posted via a free Usenet account from http://www.teranews.com

Useless propeller
 

"Peter" wrote in message oups.com...
|
| Thom Stewart wrote:
| Oh Bull **** Pete
|
| You posted; "Reduction gearing has EVERYTHING to do with it."
|
| It seems you've elected to ignore, Prop Pitch, Prop Size, and the Medium
| it is operating in. You have also neglected to recognize throttle
| control
|
| It was just as valid as your response that reduction gearing has
| NOTHING to do with it.
|
| Try moving a 40,000 lb displacement boat with a 225HP 2 stroke outboard
| running at 8000 rpm. Then try the same thing using a 225HP diesel
| running at 1800 rpm thru a 3:1 reduction box.
|
| You oversimplified and are now trying to dig yourself out.
|
| PDW
|


Precisely so...

Paladin

--
Posted via a free Usenet account from http://www.teranews.com

Useless propeller
 

Paladin wrote:
There is no heat source in that case but the water
is not boiling.

Go to a dictionary and look up the definition of boil.
You will note that it mentions application of heat.


Well, here's your problem... you seem to think that a
dictionary is the ultimate scientific reference.

I suggest a high school physics text... don't strain
yourself trying to read it, just look at the pictures!

DSK

Useless propeller
 

Thom Stewart wrote:

OK Group,

What happened to the original statement; "Useless propeller" Let's get
back to that! Why is a Two Blade Folding Prop a Useless propeller and a
Four Blade fixed going to work better in rough, choppy sea?


Well, a two-blade folder isn't really useless, it has it's
own uses and unfortunately that means it will not do as good
a job driving the boat under less-optimal conditions. OTOH
it will allow the boat to sail much better.

The problem with most folding props is
1- they are expensive, leading most people to buy the size
smaller than they really need
2- the hubs often develop some play, allowing the blades to
twist unfavorably and lose power

These two things are why they don't work well in reverse and
don't work well in choppy water.

I have a little experience with the Luke three blade
feathering prop, which is expensive but a very practical
alternative.

A good friend of mine had a small keelboat with a big
2-blade folder... the boat was very slow under power. This
was the opposite case of above, the previous owner had gone
for "conspicuous consumption" and outfitted the boat very
expensively but not efficiently. Among other things, the
prop was pitched for much higher RPM. When we were motoring
out to a race one time, we discussed the issue and since
thenengine reached full RPM easily, there was no reason not
to adjust the pitch. After two successive adjustments the
boat went almost 2 knots faster under power. It also motored
quite well in rough water... certainly much better than the
same type boat with an outboard.

Fresh Breezes- Doug King

Useless propeller
 

"DSK" wrote in message .. .
| Paladin wrote:
| There is no heat source in that case but the water
| is not boiling.
|
| Go to a dictionary and look up the definition of boil.
| You will note that it mentions application of heat.
|
|
| Well, here's your problem... you seem to think that a
| dictionary is the ultimate scientific reference.
|
| I suggest a high school physics text... don't strain
| yourself trying to read it, just look at the pictures!
|
| DSK
|

The dictionary is the ultimate language reference and since things are discussed using
language the discussion must share common ground of accepting definitions of words.
Much confusion can be avoided if common ground is adhered to by those discussing even
scientific concepts. Ideally, scientific concepts need to be discussed using math as
there is agreement upon math entities. But since you have shown that you cannot even
grasp language it demonstrates how futile it would be to use math to discuss this
word "boil".

Nobody invited you into this discussion with your ignorant statements. Butt out with your
unwanted butting in...

Paladin

--
Posted via a free Usenet account from http://www.teranews.com

Useless propeller
 

Pal(?)

Once again you've neglected to consider the drag created when not using
the engine.

Please look at the Subject heading. Then try to remember what kind of
Prop was being referred two AND in what kind of sea condition were being
described.

You can "Color me Gone" with this reply.




http://community.webtv.net/tassail/ThomPage

Useless propeller
 

The propeller does boil the water. It is a scientific fact and I shall offer
irrefutable proof:

http://www.brooklyn.cuny.edu/bc/ahp/MBG/MBG4/Joule.html

Quotes:

"In the following years he took to measuring the amount of heat generated by
every mechanical process he could think of. He enclosed wooden paddles
inside an insulated container and used a falling weight to turn a shaft and
churn the paddles. Friction caused the water in the container to heat up,
and Joule measured the heat change. From this the work done could be
compared with the amount of heat that had been produced.

By 1843 he was ready to publish. Called the mechanical equivalent of heat,
this is value for the amount of work required to produce a unit of heat, and
is calculated as 41,800,000 ergs. (One erg is the work done in moving a one
gram mass through a one centimeter distance)."



So, as one can plainly see that in the mid-1800's it was recognized that the
churning of propellers heat the water. In the case of the cavitating
propeller, the slippage is so great that the energy that would normally go
into propelling a great ship forward goes, instead, into raising the caloric
content of the fluid medium surrounding said propeller causing boiling and
cavitation.

Hence, the propeller boils the water, causing cavitation.

My tea kettle has a propeller in it and boils water quite quickly with no
application of heat.

Useless propeller
 

"Thom Stewart" wrote in message ...
| Pal(?)
|
| Once again you've neglected to consider the drag created when not using
| the engine.
|
| Please look at the Subject heading. Then try to remember what kind of
| Prop was being referred two AND in what kind of sea condition were being
| described.
|
| You can "Color me Gone" with this reply.


Buh bye!

Paladin

--
Posted via a free Usenet account from http://www.teranews.com