What was the other motor? Then go find the specs for it and check the gear ratio
vs the current motor.
"Bob La Londe" wrote in message news:1105661534.f96f0d40b2f504084e2179296c7d0aca@t eranews...
"Wayne.B" wrote in message
...
On Wed, 12 Jan 2005 22:14:46 -0700, "Bob La Londe"
wrote:
The thing that gets me is the boat literally leaps out of the water. It
does perform at the low end like its under propped for top end. Should I
be
looking for a 16P prop?
Yes, I know 6000 rpm is above the max reccommended WOT rpm. I only ran
it
at that speed for long enough for speed to stabilize so I had a baseline
to
compare with. Max reccomended rpm is 5500.
=============================================
I think you're kind of answering your own question here. Go for it
and stop over reving your engine before you blow something.
No I didn't answer my own question, nor is ten or even twenty seconds at WOT
500 RPM above max. rec. going to blow anything on a modern Mercury outboard.
I ran another 50 HP motor on that boat, and with a 11 1/2 Pitch prop it
pushed the boat to 32 mph at 5300 RPM.
I posted:
"Either the gear ratio of that lower unit is way different from other
outboards I have run or the tach has to be way off.
What do you think? Is that in keeping with that motor and prop?"
I want to know why the motor can push a 14P prop to 6000RPM at that speed
when a much shorter pitch prop on another motor pushed it close to the same
speed at 700 RPM less. The numbers don't add up. Hence my comments that
either the tach is off or the lower unit is geared substantially differently
than my other motor.
If the tach is off then by just jumping up a couple inches of pitch I will
be continuously lugging my motor, and I should instead be looking for a new
tach. Lugging the motor continuously would do damage to my motor. If the
tach is correct then there must be another cause for the discrepancy such as
a different gear ratio in the lower unit. Then going up in prop size would
be exactly what I should do.
My speed measurements are done with a GPS with WAAS enabled.
I was hoping (I know probably in vain) that somebody who had actual
experience with newer model Mercury outboards might volunteer an experienced
opinion about the ratio of PITCH : RPM : SPEED as it relates to my numbers
and let me know if it was mostly likely correct or a bad tach.
Bob La Londe
www.YumaBassMan.com