You are exactly right. Dropping to a 21 will increase rpms by about 300 and
drop your speed. You would have to increase rpms by 500 to maintain the
same speed w/ a 2" drop in pitch.

However, something does not add up based on the numbers.
23 x 5400 / 1056 / 1.86 = 63 mph. That means you have a 60% efficiency.
Even if you had a 2:1 gearcase you still have a theoritical speed of 58 mph
which gives a 65% efficiency.



--
Tony
my boats at http://t.thomas.home.mchsi.com

"Short Wave Sportfishing" wrote in message
...
On Thu, 09 Sep 2004 01:00:54 GMT, "Tony Thomas"
wrote:

Not sure why you say this Rob. A 21 double cupped will definetly help on
the hole shot but will overrev by about 250 rpms. The double cupping
adds
bite and creates extra drag which reduces the rpms without adding pitch.
It
will also slow the boat down considerable due to the fact that your now
turning a 21 instead of a 23. Expect about 5 mph drop in top end if you
keep the rpms at 4600 (don't overrev).

As for the Torque Shift prop - I don't care for the maintenance of the
prop
springs and the cracked hubs and the stress on the lower unit. They do
work
but are not worth the money and maintenance costs.

I have a question for you.

My friend who has the engine problems also has a prop problem. He is
currently swinging a 14 1/2 x 23 on an Evinrude 200 FICHTand gets
about 38 mph at 5400 rpm WOT fully trimmed out. He can change pitch
which changes RPM but no relative increase in speed - in fact with a
21, he got 5700 RPM and lost four mph. The engine is properly
installed, etc.

Any idea why?

Later,

Tom