While true that props can be built to have tail/stern lift and/or bow lift.
This does not come into play at lower rpms that your talking about to
maintain plane. Higher rpms are required to have any effect. So prop lift
will have no effect.

As stated before - planing speed of a hull is planing speed. No prop is
going to change that. A whale tail will which in effect changes the hull
design by adding a hook to push the bow down. A more efficient prop will
allow you to achieve the theoritical plane speed but it will not change it.


--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"Calif Bill" wrote in message
ink.net...
Depending on the cup, etc of a prop, it can induce lift in the transom
area.
So a prop can help in getting up on and maintaining plane.

"NOYB" wrote in message
nk.net...

"Gene Kearns" wrote in message
...
On Sat, 18 Dec 2004 11:01:15 -0500, MikeG
wrote:


The planning speed thing was what was bothering me also. It's the main
reason I got to thinking about re propping.

The present prop is in pretty sad shape. I'm hoping that even without
changing anything a new prop of the same spec's will show an
improvement
in that area.


The direction of this thread seems to have made a left turn and gotten
me a bit lost....

The *prop,* per se, has *nothing* to do with the speed at which a boat
planes. While, you may well pick up some efficiency and/or top end
with a new prop, it won't change the planing speed at all.

the prop has nothing to do with the speed at which the boat planes, but
it
does affect the ability of the boat to maintain that speed before falling
off plane. For instance, his boat may actually plane at 17 mph...but his
current prop can't maintain the boat on plane at 17 mph, and it quickly
falls off plane. It sounds to me like 20 mph is simply the minimum speed
at
which he's able to *maintain* plane...and he's calling that his minimum
planing speed. Changing props won't change the speed at which the boat
planes, but it very well may change the boat's ability to maintain a
lower
planing speed. I'd say try the 4-blade. If he drops the pitch, the
engine
will overrev...unless he also increases diameter to compensate. Of
course,
he could also have a prop shop add cupping to the blades, but then it
becomes even less of a science and more of trial and error.