Trying to select a prop for my 3.5HP Mercury 4 cycle on my Bass Raider 10E. Maybe some of you guys have some guidance.
Speed isn't the primary concern here (oh yes it is ) but optimal WOT RPM for this motor.
The factory prop for this motor, sold under a few different badges is a semi weedless 3 blade 7.4" diameter and 7" pitch.
For emergency use I bought a spare 7.25"X6" which I guess is the factory prop on the similar 2.5HP.
There is an aluminum prop available that would fit (I think) advertised as 7.4"X5.7".
That's it, 3 props. The plastic props don't look to be suitable for thermal shaping while the aluminum might.
We normally run with at least 400 pounds including motor.
Once with 500 pounds with a 29 battery and 30 trolling motor and once just for a cute video with one person but no data for that run.
I will try again with the lightest load I can (after the hurricane).
Here are my data points with the 10E, both on the same day, same water and wind conditions:
7.4"X7", swept area (blade minus hub) of 40 sq.in., 4840rpm (WOT), GPS speed 5.4 mph.
7.25X6", swept area of 38 sq.in., 6000 rpm(WOT), GPS speed @ 5500 rpm 4.8 mph.
The 7.4"X7" has 4.5% more swept area, 16.7% more pitch, and gets 12.5% more speed, but runs 24% less rpm at WOT (13.6% less 5500/4840)
The smaller prop just doesn't load up the motor. Speed at 5500rpm was about the same as 6000rpm.
I'll probably buy the 7.4X5.7 aluminum and try to bend and cup to something between 6 and 7 pitch.
My goal is to get something around 5500 rpm and suck as much power out of this 3.5hp as I can
Advise??
