well; after trying a bunch of props; here's a rundown on the results....
boat needed 4200-4600 RPM at WOT

Original prop was a SS 14x19 3 blade -- WOT 3800 rpm

aluminum 15x17 3 blade - WOT 4950
aluminum 14.5 x 19 3 blade WOT 4250

the 4 blade dropped it 150; so it was too low for for reasonable use; but
getting on plain & staying there was great.

The difference in RPM from the SS to Alum 15x17 is being attributed to the more
agressive cupping on a SS blade.

so I'm much happier with the alum 14.5x19 -- but will try some some 4 blade
15x18 props to see how they do ... but that won't be until much later in summer.

Thought it was interesting about the difference in cupping would make that much
of a difference.

aluminum prop blades have more flex then SS blades.



"Josh Assing" wrote in message
...
well; after trying a bunch of props; here's a rundown on the results....
boat needed 4200-4600 RPM at WOT

Original prop was a SS 14x19 3 blade -- WOT 3800 rpm

aluminum 15x17 3 blade - WOT 4950
aluminum 14.5 x 19 3 blade WOT 4250

the 4 blade dropped it 150; so it was too low for for reasonable use; but
getting on plain & staying there was great.

The difference in RPM from the SS to Alum 15x17 is being attributed to the
more
agressive cupping on a SS blade.

so I'm much happier with the alum 14.5x19 -- but will try some some 4
blade
15x18 props to see how they do ... but that won't be until much later in
summer.

Thought it was interesting about the difference in cupping would make that
much
of a difference.

Lost In Space/Woodchuck wrote:
aluminum prop blades have more flex then SS blades.


Try flexing your aluminum prop blades & let us know how that works out.

Rob




"Josh Assing" wrote in message
...
well; after trying a bunch of props; here's a rundown on the results....
boat needed 4200-4600 RPM at WOT

Original prop was a SS 14x19 3 blade -- WOT 3800 rpm

aluminum 15x17 3 blade - WOT 4950
aluminum 14.5 x 19 3 blade WOT 4250

the 4 blade dropped it 150; so it was too low for for reasonable use; but
getting on plain & staying there was great.

The difference in RPM from the SS to Alum 15x17 is being attributed to the
more
agressive cupping on a SS blade.

so I'm much happier with the alum 14.5x19 -- but will try some some 4
blade
15x18 props to see how they do ... but that won't be until much later in
summer.

Thought it was interesting about the difference in cupping would make that
much
of a difference.

ACTUALLY the higher rpm on the aluminum of the same specs is due to flex.
They tend to flatten out the equivalent of an inch or two of pitch.

--
Steve Barker







"Josh Assing" wrote in message
...
well; after trying a bunch of props; here's a rundown on the results....
boat needed 4200-4600 RPM at WOT

Original prop was a SS 14x19 3 blade -- WOT 3800 rpm

aluminum 15x17 3 blade - WOT 4950
aluminum 14.5 x 19 3 blade WOT 4250

the 4 blade dropped it 150; so it was too low for for reasonable use; but
getting on plain & staying there was great.

The difference in RPM from the SS to Alum 15x17 is being attributed to the
more
agressive cupping on a SS blade.

so I'm much happier with the alum 14.5x19 -- but will try some some 4
blade
15x18 props to see how they do ... but that won't be until much later in
summer.

Thought it was interesting about the difference in cupping would make that
much
of a difference.

Steve Barker wrote:
ACTUALLY the higher rpm on the aluminum of the same specs is due to flex.
They tend to flatten out the equivalent of an inch or two of pitch.


Prove it.

Rob

The OP just did.

--
Steve Barker







"trainfan1" wrote in message
news
Steve Barker wrote:
ACTUALLY the higher rpm on the aluminum of the same specs is due to flex.
They tend to flatten out the equivalent of an inch or two of pitch.


Prove it.

Rob

On Mon, 2 Jul 2007 23:52:57 -0500, "Steve Barker"
wrote:

The OP just did.


no I didn't....
the SS had a more agressive cupping to the blade; the props do not have the same
physical prop design; so even tho they're the same pitch; they are different
props...

You all can twist the facts all you want. Pitch is pitch. In theory, a
given pitch goes xx inches through the water in one rotation. Given this,
the stainless and the alum will do the same inches in one revolution.
Until, that is, you put some power behind it and the aluminum flattens out a
bit. Thus the higher rpm for the same pitch. You can cup this and cup
that, but the fact is the aluminum flexes and loses pitch. Period.

--
Steve Barker







"Josh Assing" wrote in message
...
On Mon, 2 Jul 2007 23:52:57 -0500, "Steve Barker"

wrote:

The OP just did.


no I didn't....
the SS had a more agressive cupping to the blade; the props do not have
the same
physical prop design; so even tho they're the same pitch; they are
different
props...