Currently, I have a 10.6 Diameter, 12 pitch, 4 blade prop, aluminum.
I was reading a little bit about what pitch actually is and I understand that it is how many inches per turn the prop will move you. I also read that a outboard motor needs to be at a recent RPM to actually work. At first, I was thinking, well, let me get a 15 Pitch prop and scoot along. From my understanding though, the higher the pitch the lower the RPM. To low of a RPM apparently can damage your motor. Is that correct?
So, here is my real question. If I went with a 10.625 Diameter, 13 Pitch, 4 blade prop, Stainless Steel. What do you think will happen?
Last Edit: May 7, 2017 21:56:35 GMT -1 by rhinobait
Post by Bob Smith (Porko) on May 8, 2017 1:38:35 GMT -1
First of all, too low of an RPM will not hurt your motor. Run above the recommended max RPM is definitely bad for the motor. The old adage that the pitch is distance the prop will move you in a revolution, is theoretical. That's how they determine the pitch (in a perfect world). The weight of the boat the height of the motor, the center of gravity of the boat all play into the equation. Something had to have changed on the prop if you lost 4-5 mph, with everything else unchanged on your setup. You may need to ask the prop shop exactly what they did?
I could run about 5800 RPM and run right at 30 - 29.5 MPH. Now at the same RPM I am at 26 MPH. I only have a 60 HP, so, every little bit helps. Plus, recently, I was a Co-Angler in a Ranger that was 250HP, So, my boat really feels like it is sitting still now - haha.
Last Edit: May 8, 2017 11:22:17 GMT -1 by rhinobait
Holy crap!!! I am now running at 5900 WOT, with a MPH OF 40!!!! Well worth it in my book.
What is the redline for that motor?
I am not really sure. The only thing I found in the manual is do not run at WOT for more then 5 minutes at a time. I do know that the motor will shut down when it gets to hot and beeps (Well from what I have read).
Post by Bob Smith (Porko) on May 12, 2017 0:38:10 GMT -1
I run a 225 Optimax on my boat and the redline is 5700 RPMs, you can run more than that, but it's not recommended. (I think the main thrust bearings are rated for 6000). I am not sure what a small block motor like yours should redline, but I wouldn't hold her at 5900 RPMs for long periods of running.