prop question

[Fred Bradley]

I ordered the optimax 115 on my pro team 190. Runs and performs great and has been very reliable so far, no issues. It is a 2011 model. When it came into the dealer i found that it had a 21 inch aluminum prop, which i thought 19 was standard, either way, i have found that it has a sweet spot at 5200 rpms, around 47.8 mph on gps. If i bump the trim up a hair higher to 5400 rpms, i actually start to lose speed and i can feel a little drag on the motor, at 5600 rpms it loses about 2 mph. Should i just run it at its sweet spot, 5200 rpms or consider downsizing a pitch on the prop, maybe a 20 pitch. I am also considering a stainless steel laser 11 prop. Just wanted a few opionions. Its my understanding for every one inch downsizing in prop pitch i will gain around 200 rpms. Its also my understanding that the aluminum prop will flex, what would be the ideal size prop in stainless seeing how it will not flex, still the 21, 20, or 19? Dont want to lose any top end, just like to see the rpms be a little more matched according to mercury marine specs. Thanks, Fred.

 

[Bob Bourget2]

The 21" is the factory prop for that rig. If you want to go stainless, I would opt to drop down to a 20", for a little more rpm, and it will not "ventilate" when trimmed. Right around 5850, the rev-limiter will start doing it's job.

 

[Fred Bradley]

Thanks Bob, i sure appreciate all of your insight, and im sure the others on here do as well, you should be paid for your advice! I did hit the rev limiter once at around 5850 and the alarm sounded and as i trimmed down the alarm went off. Im finding that its sweet spot is at 5200 rpms with the aluminum 21 pitch, i dont know if this is a good thing or not as far as gas consumption, all i know is i love the motor and i want to operate it at its most efficient peak of performance without losing top end. If you say go to the 20 pitch stainless, i think im gonna do it, and im assuming the laser 11 prop is what you would go with? I had a 23 pitch tempest on my nitro z-7 and loved it. If you dont mind let me know what you think. Thanks again. Fred.