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

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?

"Injam" wrote in message
news
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

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.

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.

"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

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
news
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

"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
news
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

"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