Reprop on b08 Yamaha F40

"My '08 Yammy 40hp 4-strok

"My '08 Yammy 40hp 4-stroke at WOT runs 5400 rpm. In an effort to get closer to the recommended WOT RPM of 5500-6000, I had the dealer tweak it from 4800 to 5400 and that is the best they could get out of it. I am considering repropping from a 10 1/4x14 to a 10 1/4x11, which, if I have the numbers right, should work out about right. Looking for input to my plan or other suggestions before investing in a prop. Any thoughts you may have will be appreciated."

"Gary, going down 3" of pi

"Gary, going down 3" of pitch would take you up to the extreme end of your WOT range.

Each inch of pitch will change the rpm's by about 200 - so 3" x 200 = +600 (when talking about a 3 blade prop).

That may be a little too close for comfort because if you ever get out and run "light" (less gear or fuel or people on board) you run the risk of over revving the motor.

You may want to consider a 4 blade prop (11 pitch). It would keep you safely in your range, give you a better hole shot and let you keep the boat on plane at a lower speed (saving gas in the process).

The 4th blade would reduce the overall rpm increase to approx 500, and if you also went with cupped blades, that would shave off another 50 rpms.

Ya, lot's of choices to consider

The more you run the boat you will also notice that it reacts differently depending on the season.

In the summer when the air is hot/humid you can easily lose 500 rpms simply because your motor has difficulty "breathing". Under those conditions your 11 pitch choice may be perfect, but a 12 or 13 pitch may be way better suited for spring/fall/winter running when the humidity is almost non-existant and the temperatures are cool.

So yes, absolutely try and prop your boat to get it into it's WOT range, it will run cleaner (less carbon build-up) and help prevent detonation in the cylinders - but be aware that no "one" prop will serve all your needs - most rigs will require, at minimum, two different props simply to account for seasonal variations, and if you "multi-purpose" the boat (ski, fish, wakeboard, cruise", you could end up with 4 or more props for the same rig..."

"Graham, thanks for the good i

"Graham, thanks for the good info. I always like to check my thinking with others because my brain likes to go on vacations without me sometimes, plus others fill in info that I am not aware of that allows me to make the fewest mistakes. Thanks again
Gary"