I'm trying to understand propellers
 

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.

For rec.boats this thread is like a group hug ;)

I'm trying to understand propellers
 

Shortwave Sportfishing wrote:
But there isn't a "difference".

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.

You sure have a knack for obfuscation. That wasn't the question.

-rick-

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?


Momentum equals mass multiplied by velocity. If the cars are of equal weight
and the same speed the momentum is equal. The ET doesn't have much to do
with it.

If you shut the engines off neither car will accelerate, both will
decelerate due to friction losses.

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...
On Sat, 4 Mar 2006 08:44:34 -0500, "John Wentworth"
wrote:


"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?

Momentum equals mass multiplied by velocity. If the cars are of equal
weight
and the same speed the momentum is equal. The ET doesn't have much to do
with it.

If you shut the engines off neither car will accelerate, both will
decelerate due to friction losses.

I don't know where you learned your physics, but I can guarantee you
that isn't the case at all.

What part of my comments do you disagree with?

The definition of momentum? Momentum is not acceleration, just mass times
velocity. Acceleration is an increase in velocity.

That both cars will decelerate?
To accerate the cars would require additional force to be applied, without
the engines running there will not be any additional force. Absent that
additional force, what would make the car go faster? Are you saying that
force isn't required to accelerate an object? Or that frictional losses will
not cause deceleration in the absence of sufficient applied force to
counteract those loses?

Take a look at
http://www.glenbrook.k12.il.us/GBSSC...tum/u4l1a.html

I'm trying to understand propellers
 

On Fri, 03 Mar 2006 20:45:38 GMT, Shortwave Sportfishing
wrote:

I think I'm not bored anymore. :)

I think you were right Tom, the 250 hp will be faster...

I'm trying to understand propellers
 

Hello,

When I posted my first scenario I had been looking at Yamaha four stroke
outboards. According to Yamaha the 250 hp weighed about thirty pounds more
than the 200 hp. I thought the prop would slip more pushing the heavier
outboard. Thirty pounds is not much, but if everything being equal I thought
the 200 hp would slowly pull away. Also if you go to Mercury's prop selector
when it gives you a top speed I think it is using a theoretical pitch in
it's calculation. This is actually what got me thinking about this scenario.
I would put in the same boat but different horsepower outboards. It would
come back and sometimes suggest the same pitch prop, but would list a faster
top speed for the larger motor. When I went back and looked at it closer, it
does list a theoretical pitch and they are always different.

Now if I could just figure out to get $10.00 out of y'all every time y'all
posted to this thread.

Sincerely,

Injam

"Shortwave Sportfishing" wrote in message
...
On 3 Mar 2006 12:24:21 -0800, "M" wrote:


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 .. .

I think I'm not bored anymore. :)

I'm trying to understand propellers
 

On Sat, 04 Mar 2006 16:58:03 GMT, "Injam"
wrote:

Now if I could just figure out to get $10.00 out of y'all every time y'all
posted to this thread.

Good plan, we could all be filthy rich if you can figure it out.

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...
On Sat, 4 Mar 2006 09:46:51 -0500, "John Wentworth"
wrote:


"Shortwave Sportfishing" wrote in message
. ..
On Sat, 4 Mar 2006 08:44:34 -0500, "John Wentworth"
wrote:


"Shortwave Sportfishing" wrote in message
m...

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?

Momentum equals mass multiplied by velocity. If the cars are of equal
weight
and the same speed the momentum is equal. The ET doesn't have much to do
with it.

If you shut the engines off neither car will accelerate, both will
decelerate due to friction losses.

I don't know where you learned your physics, but I can guarantee you
that isn't the case at all.

What part of my comments do you disagree with?

The definition of momentum? Momentum is not acceleration, just mass times
velocity. Acceleration is an increase in velocity.

That both cars will decelerate?
To accerate the cars would require additional force to be applied, without
the engines running there will not be any additional force. Absent that
additional force, what would make the car go faster? Are you saying that
force isn't required to accelerate an object? Or that frictional losses
will
not cause deceleration in the absence of sufficient applied force to
counteract those loses?

Take a look at
http://www.glenbrook.k12.il.us/GBSSC...tum/u4l1a.html

I apologize - it was an intemperate remark and uncalled for.

Having said that, I just don't want to get into it anymore.

Pansy.

I'm trying to understand propellers
 

Shortwave Sportfishing wrote:
On Fri, 03 Mar 2006 23:47:29 -0800, -rick- wrote:

You sure have a knack for obfuscation. That wasn't the question.

I know that.

I was bored.

Don't you ever get bored?

Not really... I still work, read, boat, fish, exercise, play
guitar, etc. There's not enough hours in the day. As soon
as the wife gets the coolers packed and the herring plug cut
we're heading out after some spring Chinook.

How's the shoulder coming along?

-rick-

I'm trying to understand propellers
 

Calif Bill wrote:
"Shortwave Sportfishing" wrote in message

Having said that, I just don't want to get into it anymore.

Pansy.

[grin]