Posts: 3511
Location: Elk River, Minnesota | Hiya,
after doing a bit of digging, the 15 pitch is right in the ballpark for what you should be at. With a maximum rpm of 6400, I would suggest going down in DIAMETER, though, which will get you closer to the ballpark for your motor RPMs. The holeshot will increase dramatically, and with the motor being able to turn the prop better, you might see an increase in speed as well.
This particular motor is not going to be a speed demon at all with a gear ratio of 2.33:1, It has the low end torque for pontoons and big eared props, but it also has the availability to use a smaller overall diamter to get things moving at speed as well.
NOTE: This is assuming there are props available in a smaller overall diameter, but the same hub size as well. I will do a bit of checking to see what I can find out in this area.
My buddy also has the larger diameter as well...stinks coming out of the hole, but going down in diameter will, in effect help hole shot as well since the motor can turn up to higher rpms quicker.
If you take a look at the mercury website, they have performance tests you can look at with something comparable to your boat. I looked at an alumacraft competitor 1750 which is probably a touch lighter than your boat, but they are reaching the 6100 rpm mark with a 12.8 x 17 pitch...a full inch smaller in diameter than what you have currently. I believe they were testing the "spitfire" propeller on those...Which is a 4 blade prop...that helps with hole shot and handling.
In most cases there is a limit to what the motor can do and RPM's drop dramatically if you increase diamter or pitch. For example, my recently traded yamaha 90 2 stroke could turn a 17 pitch prop to 5400 RPMs, but as soon as I put a 19 pitch on, it dropped to 4600 at trim... It just could not do it... So...by reducing your overall diameter (not hub size...just overall diameter) you can get an increase as well.
So...if you can get to a shop that has any sort of a demo prop program, you might be able to find a few props to try and head to the water and test them. One will stand out among the others for overall performance, holeshot and top end.. When propped well, the boat will just seem to float along at cruising speed... Nice and comfy, yet responsive when you need it.
Steve
Edited by VMS 9/18/2012 10:16 AM
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