I'm trying to understand propellers
 

"Harry Krause" wrote in message
. ..

If the 200 is properly propped to hit 6000 rpm at WOT, then the 250 is
going to over-rev 6000 with the same prop.

Yup.

RCE

I'm trying to understand propellers
 

On Sun, 26 Feb 2006 21:45:35 GMT, Shortwave Sportfishing
wrote:

Ah what does he know - he owns a Grand Banks. :)

With a really big (and expensive) pair of propellers.

I'm trying to understand propellers
 

On Sun, 26 Feb 2006 16:35:18 -0500, "RCE" wrote:

The bigger engine will get to 6000 RPM faster ... and *it* will probably
produce more prop slip in the process. Not unlike burning rubber in your
Vette.

Yes, because the bigger engine will presumably have more torque.

I'm trying to understand propellers
 

On Sun, 26 Feb 2006 21:48:29 GMT, "Injam"
wrote:

What if we ran these boats for 100 miles?
Who would get there first?

100 miles at the same speed, uhhhh, that's a tough one.

Got it.

Who ever started first. :-)

I'm trying to understand propellers
 

On Sun, 26 Feb 2006 21:39:48 GMT, "Injam"
wrote:

Say you were going to buy a Triton 220LTS. You have a choice of Yamaha
F250hp V6 Four Stroke or F225hp V6 Four Stroke. If you went with the 250 hp
what diameter and pitch propeller would you buy? Also what diameter and
pitch propeller would you buy for the 225 hp?

Picking the right propeller for a given boat and engine is as much art
as science. It even gets down to how much fuel, and how many
passengers you expect to carry, and what conditions do you want to
optimize. I would go with dealer or manufacturer recommendations for
a starter.

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...

You are discounting inertia and momentum as a factor. More horsepower
will overcome base inertia and add momentum meaning that the larger
engine will have to work less to maintain, or even increase, speed
given the same RPM.

Agreed. But in this exercise all we need to deal with is sufficient power
to overcome base inertia to achieve 6000 RPM and we have stipulated that the
200 hp engine can, for purposes of discussion. The rest is gearing.

RCE

I'm trying to understand propellers
 

Thanks to all who responded. It helped---------kinda.

Sincerely,
Injam

"Wayne.B" wrote in message
...
On Sun, 26 Feb 2006 21:39:48 GMT, "Injam"
wrote:

Say you were going to buy a Triton 220LTS. You have a choice of Yamaha
F250hp V6 Four Stroke or F225hp V6 Four Stroke. If you went with the 250
hp
what diameter and pitch propeller would you buy? Also what diameter and
pitch propeller would you buy for the 225 hp?

Picking the right propeller for a given boat and engine is as much art
as science. It even gets down to how much fuel, and how many
passengers you expect to carry, and what conditions do you want to
optimize. I would go with dealer or manufacturer recommendations for
a starter.

I'm trying to understand propellers
 

"Shortwave Sportfishing" wrote in message
...
On Sun, 26 Feb 2006 17:46:11 -0500, Wayne.B
wrote:

On Sun, 26 Feb 2006 21:45:35 GMT, Shortwave Sportfishing
wrote:

Ah what does he know - he owns a Grand Banks. :)

With a really big (and expensive) pair of propellers.

On a slow boat to China. :)

Did I mention to you that my lovely and long suffering wife was so
impressed with your boat that she's been beating on me to look into
obtaining one?

I've been telling here that it's way to expensive and besides, I can't
tow it.

~~ mutter ~~

Bring her over to Kingman this spring or summer. Mrs. E. would love to give
her a tour of a smaller cousin to Wayne's boat. Maybe we'll take it out and
"open 'er up". All the way to 8.5 kts.

RCE

I'm trying to understand propellers
 

"Injam" wrote in message
ink.net...
Thanks to all who responded. It helped---------kinda.

Sincerely,
Injam


Injam,

Like Wayne said, the right prop for your boat is going to be a bit of an
experiment exercise. If you are buying a new boat, confirm with the dealer
that he will assist you in obtaining the optimum pitch after you take
delivery and have some experience with it. A 25 hp difference in engines is
not going to be a huge factor. Things like how you load the boat, how many
people typically ride with you, etc. will probably have more of an affect.
The simple method is to determine what pitch allows your engine to achieve
it's recommended maximum RPM at WOT. I think you will find that a
compromise of sorts will be required though because the ideal pitch will
change, again based upon how you load the boat.

I had an old Century I/O years ago and had two props. I used the higher
pitch when I was just cruising by myself or with one other person. If four
or more people showed up for a ride, I changed the prop to a lower pitch.

RCE

I'm trying to understand propellers
 

If you are testing your new boat and find that it does not achieve
recommended maximum RPM at WOT. That would be bad for the motor right? Too
much load. Then you would change to one that is a lower gear so to speak.
And if you over compensated and the motor went over the recommended maximum
RPM at WOT. That too would be bad for the motor, right? Over revving. When
testing should you take it to the recommended maximum RPM and see if you
have any throttle left?

"Shortwave Sportfishing" wrote in message
...
On Sun, 26 Feb 2006 18:12:42 -0500, "RCE" wrote:


"Injam" wrote in message
hlink.net...
Thanks to all who responded. It helped---------kinda.

Sincerely,
Injam


Injam,

Like Wayne said, the right prop for your boat is going to be a bit of an
experiment exercise. If you are buying a new boat, confirm with the dealer
that he will assist you in obtaining the optimum pitch after you take
delivery and have some experience with it. A 25 hp difference in engines
is
not going to be a huge factor. Things like how you load the boat, how
many
people typically ride with you, etc. will probably have more of an affect.
The simple method is to determine what pitch allows your engine to achieve
it's recommended maximum RPM at WOT. I think you will find that a
compromise of sorts will be required though because the ideal pitch will
change, again based upon how you load the boat.

I had an old Century I/O years ago and had two props. I used the higher
pitch when I was just cruising by myself or with one other person. If
four
or more people showed up for a ride, I changed the prop to a lower pitch.

Very true and well stated.

The thing I would add is that most props are compromises anyway for
the exact reasons RCE, Wayne B and other have mentioned.

One of the things I did with the Ranger when I bought it was pretty
simple with regard to props. I asked what was the best prop for speed
and the best for load and split the difference.

That's what your dealer will probably do anyway.