I'm trying to understand propellers
 

On Mon, 27 Feb 2006 16:49:29 GMT, Shortwave Sportfishing
wrote:

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

You're looking at it the wrong way. The boat with the 250 hp engine
has the POTENTIAL to go faster but you have to change to a more
agressive prop, or run at a faster RPM, to make it happen. Otherwise
it's like two cars with the same tire diameter, wheels spinning at the
same speed. Doesn't matter what the horsepower is.

I'm trying to understand propellers
 

"Wayne.B" wrote in message
...
On Mon, 27 Feb 2006 16:49:29 GMT, Shortwave Sportfishing
wrote:

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

You're looking at it the wrong way. The boat with the 250 hp engine
has the POTENTIAL to go faster but you have to change to a more
agressive prop, or run at a faster RPM, to make it happen. Otherwise
it's like two cars with the same tire diameter, wheels spinning at the
same speed. Doesn't matter what the horsepower is.


Exactly. I was about to do the car analogy, but you beat me to it.

RCE

I'm trying to understand propellers
 

Aint no way Jose.
The higher HP engine could overrev with the prop matched to a lesser HP
engine. But, since revs are limited to 6000 on both engines, gear rarios are
both the same, and prop diam. pitch and cup are the same on both engines,
boat speed will be the same.
JIMinFL.
"Shortwave Sportfishing" wrote in message
...
On Mon, 27 Feb 2006 11:02:43 -0500, "RCE" wrote:


"Shortwave Sportfishing" wrote in message
. ..


I just went to the Mercury site and spec'd out a prop for an Sal****er
EF. I set up for good overall performance between a 200 and 250.

http://www.mercurymarine.com/prop_selector

Props were identical for a 20' bass boat at roughly 3000 pounds for
hole shot, mid-range performance and top speed.

There was a one degree pitch difference in a different type of prop.

So.......horsepower rules.

I think we are on two different wavelengths, and your's is short ....
Heheheh....

ROTFL!!!

Oh wait...

HEY!!!!

Are you saying that two identical boats .....

Yep.

with identical weights .....

Yep.

with identical shaft gearing in the engines ....

Yep.

and identical props .....

Yep.

one boat has 200 hp ....

Yep.

the other, 250 hp ....

Yep.

both are run side by side with the engines at a steady 6000 rpm ....

Yep.

That the 250 hp boat is going to be moving faster?

Yep.

No Way, Hosie ..

Way, Jose..

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

You also have to consider how these boats got to 6000 RPM and I'll say
it again - horsepower wins everytime.

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

In this case, it's nothing but a gearing issue, including the props.


You also have to consider how these boats got to 6000 RPM and I'll say
it again - horsepower wins everytime.

We're in agreement here - the big engine will get to 6000 RPM faster.

RCE

I'm trying to understand propellers
 

"JIMinFL" wrote in message
ink.net...

Aint no way Jose.
The higher HP engine could overrev with the prop matched to a lesser HP
engine. But, since revs are limited to 6000 on both engines, gear rarios
are both the same, and prop diam. pitch and cup are the same on both
engines, boat speed will be the same.
JIMinFL.

I've got a feeling that by the time we convert Tom to think gears instead
of horsepower in this exercise, the original poster will be on his third or
forth boat and laughing his ass off at us.

RCE

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

You also have to consider how these boats got to 6000 RPM and I'll say
it again - horsepower wins everytime.


Ok. Time to try another analogy. (Pun intended)

Two 60 Hz, synchronous clocks.
One is running on 120 volts AC, 60 Hz.
The other is running on 110 volts AC, 60 Hz.

Is the 120 volt clock gonna run faster?

Hmmmmmmm.......

RCE

I'm trying to understand propellers
 

"RCE" wrote in message
...

"Shortwave Sportfishing" wrote in message
...

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

You also have to consider how these boats got to 6000 RPM and I'll say
it again - horsepower wins everytime.


Ok. Time to try another analogy. (Pun intended)

Two 60 Hz, synchronous clocks.
One is running on 120 volts AC, 60 Hz.
The other is running on 110 volts AC, 60 Hz.

Is the 120 volt clock gonna run faster?

Hmmmmmmm.......

RCE


An aside. Friend of mine moved to England and to manage an office there.
None of the local people would tell him why when he complained his clock was
running slow. And he was also an EE.

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...
On Mon, 27 Feb 2006 06:45:19 GMT, "Calif Bill"
wrote:


"Injam" wrote in message
ink.net...
Why? If the propellers are turning at the same RPM and they have the
same
pitch, why would the 250 hp be faster?


"Harry Krause" wrote in message
. ..
Injam wrote:
Hello,

I'm trying to understand propellers.

If you have two identical boats, but the outboard horsepower ratings
are different. One boat has a 200 hp and the other a 250 hp. Both
motors
have the same Gear Ratio. If the propellers are identical and the RPM
of
the outboard is the same on each boat. Say 6000 RPM. Because of the
weight advantage will the 200-hp boat be faster than the 250 hp? I'm
thinking less weight less slippage otherwise they would be going the
same speed.

If the 200 hp engine is properly propped, the 250 hp engine will most
likely be underpropped with the same prop. The weight diff between a
200
hp and a 250 hp is not usually significant, certainly not enough t0
canel
out a 25% increase in hp.

Now, to your question...the 250 still might be faster, even if it is
underpropped.

It will be faster to the same speed. But, the 2 engines should not have
the
same pitch prop. The 250 hp will overspeed with the correct pitch for the
200 hp. Same pitch and same RPM, other than a weight difference, both
boats
would be the same speed.

That's not the point. The point is that both run at 6000 RPM. Over
rev isn't an issue.

The issues as I understand them would point to horsepower being the
determination.

As long as you can turn that same prop at 6000 RPM the boat will move at the
same speed. If I put your vette engine in my boat, at 3200 RPM I am still
at the same speed as my 330 mpi. It does not know that there is an extra
300 hp available.

I'm trying to understand propellers
 

On Mon, 27 Feb 2006 12:52:27 -0500, Harry Krause
wrote:


I pointed this out last week. Also, the boat with the larger HP engine
will accelerate faster to its top speed:

Not true...flat out wrong

more torque, winds up to WOT
faster.

Huh? What does that mean? "WOT" is a throttle position, ie; "wide
open".

What kind of boat do you have again?
__

"It's just about going fast...that's all..."

http://home.columbus.rr.com/ckg/

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...
On Mon, 27 Feb 2006 13:16:25 -0500, "RCE" wrote:


"Shortwave Sportfishing" wrote in message
. ..

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

You also have to consider how these boats got to 6000 RPM and I'll say
it again - horsepower wins everytime.


Ok. Time to try another analogy. (Pun intended)

Two 60 Hz, synchronous clocks.
One is running on 120 volts AC, 60 Hz.
The other is running on 110 volts AC, 60 Hz.

Is the 120 volt clock gonna run faster?

Hmmmmmmm.......

No, because the clock is dependent on slicing the 60 cycles and is not
dependent on voltage - in a perfect world that is.

Ok. In the exercise we have been discussing, under the conditions
stipulated to, both engines are slicing 6000 RPM in the same manner as the
clock. The extra 20 volts or 50 hp does not matter.

Hmmmmmmm???????


RCE

I'm trying to understand propellers
 

"Netsock" wrote in message
...
On Mon, 27 Feb 2006 12:52:27 -0500, Harry Krause
wrote:


I pointed this out last week. Also, the boat with the larger HP engine
will accelerate faster to its top speed:

Not true...flat out wrong

more torque, winds up to WOT
faster.

Huh? What does that mean? "WOT" is a throttle position, ie; "wide
open".

What kind of boat do you have again?
__

"It's just about going fast...that's all..."

http://home.columbus.rr.com/ckg/

Now don't go screwing this up, Netsock. We're making progress here.

RCE

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...


Ok, you win - I give in.

Pansy.

RCE :-)

I'm trying to understand propellers
 

I'm trying to understand propellers
 

If we use a 24" pitch propeller and there was no slippage, both boats would
travel 12,000 feet every minute at 6000 RPM.

With the same propeller on each boat the 250 hp boat would over rev at WOT.
So the helmsman would have to back off to keep it at 6000. The difference in
weight of the motors is about 30 lbs. Probably not going to be much of a
factor. The 250 might get to 6000 more quickly, but once at 6000 I think
both boats would be traveling at the same speed.

Thanks again,
Injam

"Injam" wrote in message
ink.net...
Hello,

I'm trying to understand propellers.

If you have two identical boats, but the outboard horsepower ratings are
different. One boat has a 200 hp and the other a 250 hp. Both motors have
the same Gear Ratio. If the propellers are identical and the RPM of the
outboard is the same on each boat. Say 6000 RPM. Because of the weight
advantage will the 200-hp boat be faster than the 250 hp? I'm thinking
less weight less slippage otherwise they would be going the same speed.



Sincerely,

Injam

I'm trying to understand propellers
 

"Helmsman" what was I thinking! I meant boat driver.

"Injam" wrote in message
ink.net...
If we use a 24" pitch propeller and there was no slippage, both boats
would travel 12,000 feet every minute at 6000 RPM.

With the same propeller on each boat the 250 hp boat would over rev at
WOT. So the helmsman would have to back off to keep it at 6000. The
difference in weight of the motors is about 30 lbs. Probably not going to
be much of a factor. The 250 might get to 6000 more quickly, but once at
6000 I think both boats would be traveling at the same speed.

Thanks again,
Injam

"Injam" wrote in message
ink.net...
Hello,

I'm trying to understand propellers.

If you have two identical boats, but the outboard horsepower ratings are
different. One boat has a 200 hp and the other a 250 hp. Both motors have
the same Gear Ratio. If the propellers are identical and the RPM of the
outboard is the same on each boat. Say 6000 RPM. Because of the weight
advantage will the 200-hp boat be faster than the 250 hp? I'm thinking
less weight less slippage otherwise they would be going the same speed.



Sincerely,

Injam

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...
On Mon, 27 Feb 2006 19:54:59 GMT, "Calif Bill"
wrote:


"Shortwave Sportfishing" wrote in message
. ..
On Mon, 27 Feb 2006 06:45:19 GMT, "Calif Bill"
wrote:


"Injam" wrote in message
hlink.net...
Why? If the propellers are turning at the same RPM and they have the
same
pitch, why would the 250 hp be faster?


"Harry Krause" wrote in message
. ..
Injam wrote:
Hello,

I'm trying to understand propellers.

If you have two identical boats, but the outboard horsepower
ratings
are different. One boat has a 200 hp and the other a 250 hp. Both
motors
have the same Gear Ratio. If the propellers are identical and the
RPM
of
the outboard is the same on each boat. Say 6000 RPM. Because of the
weight advantage will the 200-hp boat be faster than the 250 hp? I'm
thinking less weight less slippage otherwise they would be going the
same speed.

If the 200 hp engine is properly propped, the 250 hp engine will most
likely be underpropped with the same prop. The weight diff between a
200
hp and a 250 hp is not usually significant, certainly not enough t0
canel
out a 25% increase in hp.

Now, to your question...the 250 still might be faster, even if it is
underpropped.

It will be faster to the same speed. But, the 2 engines should not have
the
same pitch prop. The 250 hp will overspeed with the correct pitch for
the
200 hp. Same pitch and same RPM, other than a weight difference, both
boats
would be the same speed.

That's not the point. The point is that both run at 6000 RPM. Over
rev isn't an issue.

The issues as I understand them would point to horsepower being the
determination.

As long as you can turn that same prop at 6000 RPM the boat will move at
the
same speed. If I put your vette engine in my boat, at 3200 RPM I am still
at the same speed as my 330 mpi. It does not know that there is an extra
300 hp available.

Yeah, but yours is one of those goofy jet boats. :)

I understand what every body else is saying, I just don't agree.

Goofy jetboats? Try fishing this river in your pansy Ranger.
http://media.putfile.com/zigzag63

I'm trying to understand propellers
 

"Injam" wrote in message
ink.net...
If we use a 24" pitch propeller and there was no slippage, both boats
would travel 12,000 feet every minute at 6000 RPM.

With the same propeller on each boat the 250 hp boat would over rev at
WOT. So the helmsman would have to back off to keep it at 6000. The
difference in weight of the motors is about 30 lbs. Probably not going to
be much of a factor. The 250 might get to 6000 more quickly, but once at
6000 I think both boats would be traveling at the same speed.

Thanks again,
Injam


You got it. And the digital hour meter will keep excellent time.


RCE

I'm trying to understand propellers
 

Shortwave Sportfishing wrote:
Way, Jose..

I look at it this way. There is 50 more available horsepower at 6000
RPM. Thus, it makes total sense to me that given the same factors -
meaning inertia and momentum - that 50 additional horsepower driving
the props will give better speed.

I think you take perverse pleasure in being wrong. ;-)

The given scenario was at steady state equilibrium, no
acceleration. Both motors are producing essentially the same
power unless there is a slight weight/drag difference. The
200 would be at a higher percentage of max throttle than the
250 however.

-rick-

I'm trying to understand propellers
 

On Mon, 27 Feb 2006 15:32:53 -0500, Harry Krause
wrote:


Shouldn't you be attending to your job wiring up orifices at OSU,
Greenhalgh?

LOL! Don't ya love it when somebody is caught lying, they try to shift
the focus off of them, and onto someone else by fabricating lies?

It sure is hard keeping track of all those lies, isn't it Krause?

Ahhh...to think there's a village out there with no idiot...
__

"It's just about going fast...that's all..."

http://home.columbus.rr.com/ckg/

I'm trying to understand propellers
 

On Tue, 28 Feb 2006 14:28:01 -0500, Harry Krause
wrote:

As usual, you demonstrate your ignorance.

You work as a systems specialist in housing, food services and event
center facilities,

If you were half as smart as you try to put yourself off here, you
would know that OSU is a land grant University. State titles mean
little compared to the working title. "System Specialist" covers
virtually all IT workers, and has a salary range from 40k, all the way
well into 6 figures.

And yes, I work under HFSEC, in the Student Affairs IT Division.

And if you got that far, you would see that I hold an "appointment"
(rather than a position) and you did of course read that, right?

You did read the appointment description, right?

And since I'm considered a Public Servant, my salary is public
information...you did read that, right?

Or could it be you omitted that information, because it didn't fit
into your feeble smear agenda?

and you were recently advertising for an assistant to
hang network wire for you.

I've hired quite the number of people Krause, but none ever to pull
wire "for" me, rather the position I was filling.

Or maybe there's another GREENHALGH, CHRISTOPHER KENT.

Doubtful.

It's not much of a job for as ass as pretentious as you are.

As usual, your attempts to discredit with lies and accusations
backfire again. Just as you argue (notice I did not say debate) your
political agenda, you do so by mis-information, assumptions, lies,
omission, and mis-direction.

You have yet again been shown what you really are.

Thank you.

Your welcome.

Bye.

See ya!
__

"It's just about going fast...that's all..."

http://home.columbus.rr.com/ckg/

I'm trying to understand propellers
 

On Tue, 28 Feb 2006 14:28:01 -0500, Harry Krause
wrote:


You work as a systems specialist in housing, food services and event
center facilities, and you were recently advertising for an assistant to
hang network wire for yo

And lets not forget the original thread were you demonstrated you know
nothing about props, and even the basic fundamental differences
between HP and torque...something I learned in high school.

Thank you.

Bye.
__

"It's just about going fast...that's all..."

http://home.columbus.rr.com/ckg/

I'm trying to understand propellers
 

On Thu, 02 Mar 2006 06:33:43 -0500, Harry Krause
wrote:


Yep. You're a tech support worker at Ohio State University. Hey, it's a
perfect job for an incompetent little geek like you. Be happy. In a few
years, you might graduate to the "Geek Squad" at Best Buy.

The 6th grade called.

They want their childish, immature, name-calling, lying insults back.
__

"It's just about going fast...that's all..."

http://home.columbus.rr.com/ckg/

I'm trying to understand propellers
 

Shortwave Sportfishing wrote:
On Sun, 26 Feb 2006 20:57:58 GMT, "Injam"
wrote:

If I'm screwing a wood screw into a piece of wood and my friend Charley is
doing the same thing. The wood is the same and the pitch on the screws are
the same. Screws are identical, but Charley is a lot stronger than I am. We
turn the screws at the same RPM. Will Charley screw his screw in before me?

If he's bigger and stronger, I'd bet on Charley. Even with the same
revolutions per minute, the depth of the stroke would be longer
because of Charley's available strength.

Nope, the screws are the same pitch. Therefore, if both turn one turn,
without slipping (seeing how this is a theoretical discussion) the
distance travelled will be exactly the same.

I'm trying to understand propellers
 

- Both boats would be the same fast in Theory.

The same fast. Yes boats go same fast, Tarzan.

a. The 200 HP motor could not rev up to 6000 rpm IF its a prop for the
250

In my scenario the 200hp is turning at 6000 RPM.
b. If the prop is for the 200 HP motor the 250 would rev at 6000 not be
able to put more power in the water.

I don't even know what you are saying.

c. The 250 would accelerate faster until it has reached 6000 rpm and
there have the same speed as the 200 (if it can swing the prop).

The 200hp can (swing the prop), but because of it's lighter weight the 200hp
would pass the 250hp on are about the five mile mark. At the ten
thousand-mile mark the 200hp would be approximately five thousand miles
ahead of the 250hp.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Just having a little fun. Thanks for the post. I did figure it out and I did
post my conclusion. It is in this NG somewhere.

Sincerely,

Injam

"M" wrote in message
ups.com...

Injam wrote:
If we use a 24" pitch propeller and there was no slippage, both boats
would
travel 12,000 feet every minute at 6000 RPM.

With the same propeller on each boat the 250 hp boat would over rev at
WOT.
So the helmsman would have to back off to keep it at 6000. The difference
in
weight of the motors is about 30 lbs. Probably not going to be much of a
factor. The 250 might get to 6000 more quickly, but once at 6000 I think
both boats would be traveling at the same speed.

Thanks again,
Injam

"Injam" wrote in message
ink.net...
Hello,

I'm trying to understand propellers.

If you have two identical boats, but the outboard horsepower ratings
are
different. One boat has a 200 hp and the other a 250 hp. Both motors
have
the same Gear Ratio. If the propellers are identical and the RPM of the
outboard is the same on each boat. Say 6000 RPM. Because of the weight
advantage will the 200-hp boat be faster than the 250 hp? I'm thinking
less weight less slippage otherwise they would be going the same speed.

Depending on what brand motor you have they will even weigh the same...
even if not the little difference in weight will not make a difference.

Here is how it goes:

- Both boats would be the same fast in Theory.

- In reality one of these will happen:

a. The 200 HP motor could not rev up to 6000 rpm IF its a prop for the
250

b. If the prop is for the 200 HP motor the 250 would rev at 6000 not be
able to put more power in the water.

c. The 250 would accelerate faster until it has reached 6000 rpm and
there have the same speed as the 200 (if it can swing the prop).


A similar question is:

"Is a 250 HP 2 stroke or 250 HP 4 stroke faster?"

answer is: They will reach the same top speed but the 2 stroke will
likely accelerate faster.

In reality acceleration and top speed may be different as both will be
propped and geared differently and have different torque curves. But
for top speed its peak HP that matters.

Matt

I'm trying to understand propellers
 

"Injam" wrote in message
ink.net...


Just having a little fun. Thanks for the post. I did figure it out and I
did post my conclusion. It is in this NG somewhere.

Sincerely,

Injam



Admit it. It was the clocks that did it, huh?
Maybe now you can explain it to Shortwave if he can take a break from taking
pictures of bugs.

RCE

I'm trying to understand propellers
 

Injam wrote:
- Both boats would be the same fast in Theory.

The same fast. Yes boats go same fast, Tarzan.

whatever you say



a. The 200 HP motor could not rev up to 6000 rpm IF its a prop for the
250

In my scenario the 200hp is turning at 6000 RPM.


read my post ....

b. If the prop is for the 200 HP motor the 250 would rev at 6000 not be
able to put more power in the water.

I don't even know what you are saying.

I imagine

c. The 250 would accelerate faster until it has reached 6000 rpm and
there have the same speed as the 200 (if it can swing the prop).

The 200hp can (swing the prop), but because of it's lighter weight the 200hp
would pass the 250hp on are about the five mile mark. At the ten
thousand-mile mark the 200hp would be approximately five thousand miles
ahead of the 250hp.

Thats just not true. A lot of 200 and 250 HP motors weigh exactly (!)
the same (i.e. Verado) and if one weighed 20lbs more it would hardly
noticably affect top speed.

The 200 HP would be ahead? How that?

If so the 250 would be ahead as it would accelerate up to your 6000 rpm
faster as the 200. Since EVERYTING else is the same. Same boat, same
weight, same prop. They would then continue with lead the 250 has.

Same rpm under same conditions will get the same speed. Duh.


Just having a little fun.

Getting a little insulting with "Tarzan" comments as well?

Matt

I'm trying to understand propellers
 

I have a degree in photography and I like taking photos of bugs.

Yes it was the clock thing that turned the light bulb on.

"RCE" wrote in message
...

"Injam" wrote in message
ink.net...


Just having a little fun. Thanks for the post. I did figure it out and I
did post my conclusion. It is in this NG somewhere.

Sincerely,

Injam



Admit it. It was the clocks that did it, huh?
Maybe now you can explain it to Shortwave if he can take a break from
taking pictures of bugs.

RCE

I'm trying to understand propellers
 

Sorry about that M. I was not trying to be insulting just funny.
But what I say is true. The 200hp boat would be faster.
In my scenario the 200hp boat is lighter.

Sincerely,
Injam

"M" wrote in message
oups.com...

Injam wrote:
- Both boats would be the same fast in Theory.

The same fast. Yes boats go same fast, Tarzan.

whatever you say



a. The 200 HP motor could not rev up to 6000 rpm IF its a prop for the
250

In my scenario the 200hp is turning at 6000 RPM.


read my post ....

b. If the prop is for the 200 HP motor the 250 would rev at 6000 not be
able to put more power in the water.

I don't even know what you are saying.

I imagine

c. The 250 would accelerate faster until it has reached 6000 rpm and
there have the same speed as the 200 (if it can swing the prop).

The 200hp can (swing the prop), but because of it's lighter weight the
200hp
would pass the 250hp on are about the five mile mark. At the ten
thousand-mile mark the 200hp would be approximately five thousand miles
ahead of the 250hp.

Thats just not true. A lot of 200 and 250 HP motors weigh exactly (!)
the same (i.e. Verado) and if one weighed 20lbs more it would hardly
noticably affect top speed.

The 200 HP would be ahead? How that?

If so the 250 would be ahead as it would accelerate up to your 6000 rpm
faster as the 200. Since EVERYTING else is the same. Same boat, same
weight, same prop. They would then continue with lead the 250 has.

Same rpm under same conditions will get the same speed. Duh.


Just having a little fun.

Getting a little insulting with "Tarzan" comments as well?

Matt

I'm trying to understand propellers
 

Yeah. I said in another post that the 250hp boat would have a prop that
would over rev it. The driver would have to ease off the throttle in order
to keep it at 6000 RPM.



"M" wrote in message
oups.com...

Injam wrote:
Sorry about that M. I was not trying to be insulting just funny.
But what I say is true. The 200hp boat would be faster.
In my scenario the 200hp boat is lighter.

Sincerely,
Injam



Ok. lets not worry about the Tarzan then...


Yes. If the 200 HP boat is lighter it will be faster. There you are
right. But rather than the HP the real difference is purely weight.

Matt

I'm trying to understand propellers
 

OMG people...this is so simple, I can't believe it's still going on. Two
boats, identical in every way *except* one has 50 more horses than the
other, turning a prop at 6000 rpm. At 6000 rpm, they will be traveling at
the exact same speed. Forget about the fact that the stronger engine may get
to speed faster...*AT* 6000 rpm they will be moving at the same speed! We're
talking *SPEED* here not *distance* in a given time. Of course if someone in
the 250hp boat raises a skier's spotter flag while underway, that changes
everything g.

--Mike

"M" wrote in message
oups.com...

Injam wrote:
Yeah. I said in another post that the 250hp boat would have a prop that
would over rev it. The driver would have to ease off the throttle in
order
to keep it at 6000 RPM.



"M" wrote in message
oups.com...

Injam wrote:
Sorry about that M. I was not trying to be insulting just funny.
But what I say is true. The 200hp boat would be faster.
In my scenario the 200hp boat is lighter.

yes. same prop the 250 would not go WOT ..

Your example may be simpler if you said same everything , 200 HP but
one boat heavier as the other...

More power would have to be used to push the heavier boat out of the
water thus less power would be available to push it forward...

Matt

I'm trying to understand propellers
 

On Fri, 03 Mar 2006 06:19:04 GMT, "MGG"
wrote:

OMG people...this is so simple, I can't believe it's still going on. Two
boats, identical in every way *except* one has 50 more horses than the
other, turning a prop at 6000 rpm. At 6000 rpm, they will be traveling at
the exact same speed.

Correct, but one boat will either be under-propped, or over-propped.

Forget about the fact that the stronger engine may get
to speed faster...

That would be torque, not horse power.

__

"It's just about going fast...that's all..."

http://home.columbus.rr.com/ckg/

I'm trying to understand propellers
 

How often does it need to be repeated?

The OP stated that WEIGHT of the boats is different, so top speed is
different too.

Matt

I'm trying to understand propellers
 

On Fri, 03 Mar 2006 16:25:51 GMT, Shortwave Sportfishing
wrote:

Which is faster?

How hard is this to understand?

Faster acceleration, no question. That was not the original issue
however. Two cars, one with a more powerful engine, same RPM, same
drivetrain, same tires = same speed under steady state conditions.

The same is true for two boats with the same props and identical RPMs.

That's the difference, steady state conditions, as posited in the
original propellor post.

I'm trying to understand propellers
 

On Fri, 03 Mar 2006 17:12:17 GMT, Shortwave Sportfishing
wrote:

Correct, but one boat will either be under-propped, or over-propped.

Not necessarily. According to a Mercury prop site which I posted
earlier, for a prop designed for hole shot, mid-range performance with
high top end, there is no difference between a 200 and 250 Optimax.

There are two ways that engine horsepower can be increased. One is by
increasing torque (twisting force), the other is by increasing RPMs.
Horsepower is the net result of both torque and RPM, and how you get
there influences prop selection the same way that it influences gear
ratios in a car.

I'm trying to understand propellers
 

On 3 Mar 2006 09:28:48 -0800, "M" wrote:

The OP stated that WEIGHT of the boats is different, so top speed is
different too.

I don't believe that is true. The assumption was, as I remember it,
that the weight difference between the 200 and 250 hp engines was not
that great, if any.

I'm trying to understand propellers
 

"Wayne.B" wrote in message
...
On 3 Mar 2006 09:28:48 -0800, "M" wrote:

The OP stated that WEIGHT of the boats is different, so top speed is
different too.

I don't believe that is true. The assumption was, as I remember it,
that the weight difference between the 200 and 250 hp engines was not
that great, if any.



This whole thread has become confused and out of control. :-)

RCE

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...

Look at it this way - which car has more momentum? Obviously the car
with the lower ET. If you shut off the engines exactly at 6000 rpm,
which car will continue to accelerate?

It's the same issue with the boat question and it's even more relevant
because of momentum. The fact that one boat with more horsepower
imparts more momentum means that at 6000 RPM it will be faster when it
reaches it's limits.


Two words, Tom.

Steady state.

No acceleration. Momentum and inertia of each boat is the same, other than
the slight weight difference of the engines.

That was the original, stipulated condition.

RCE

I'm trying to understand propellers
 

Shortwave Sportfishing wrote:
On 3 Mar 2006 09:28:48 -0800, "M" wrote:

How often does it need to be repeated?

The OP stated that WEIGHT of the boats is different, so top speed is
different too.

That was an assumption, not a constant. His assumption was wrong. The
only true difference was horsepower.

I dont think the OP explained clearly what he really wanted to compare.
Thus the big discussion about the issue...

I understand he wanted to show a weight difference with the different
motors rather than a power difference. Thus the 6000 RPM limit...


The question should be rephrased before this gets out of hand .. .

Matt

I'm trying to understand propellers
 

"M" wrote in message
oups.com...


I understand he wanted to show a weight difference with the different
motors rather than a power difference. Thus the 6000 RPM limit...


The question should be rephrased before this gets out of hand .. .

Matt



It's already out of hand.

The OP posed the following question (paraphrasing)

Two identical boats, identical props, identical motor shaft gears, both
running at 6000 RPM.
One has 200 hp. The other 250 hp. Which boat is moving faster? The slight
weight difference between the engines was stipulated as a non-issue.

Answer: Side by side, "steady state" (not accelerating) both are going
the same speed.

Other inputs that may or may not be valid include the fact that the bigger
engine will accelerate to 6000 RPM faster, prop slip may be different, and
other variables where not part of the original conditions set for sake of
the original question and discussion.

That's the last of this that I want to think about.

RCE

I'm trying to understand propellers
 

agree with you ...