i get alot of questions concerning propping...i typed a pretty good description of propping the boat,here-http://bhweb.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=84396#Post84396


where owner's get confused is the "i never run my boat above 3,500rpm"...it doesn't matter if you never run full throttle,if the engine can not reach it's reccomended rpm,it's no good,and the engine is overloaded-end of story...prop the boat correctly...

You may even be surprised how well the boat rides after it is propped properly. I used to think I just had to deal with some pounding with the mod-v before, now it hardly pounds and when we do come out of the water it lands much softer now. Not to mention the lower fuel burn rates and being able to run faster more comfortably. It also was not nearly as costly as I thought it would have been.

Raising or lowering an outboard just one hole can also change the ride significantly.

FinFan

before you start raising and lowering an engine on the transom,you should check the position of the cavitation plates while the boat is on plane...have an assistant run the boat for you,look over the transom,see if the cavitation plate is above or below the water...if the cavitation plates are below the water,the engine can be raised,if the plates are above the water,the engine is at a the correct height.
an engine that's mounted too high,will cause the boat to porpose,it can and will also ventilate due to the prop losing it's bite .

I just did a re-prop on our sea ray. Had a 15 pitch on it when we got it, just didnt feel right, fealt like it was working way to hard to get where it was going. Did some digging on the sea ray site and found that it was supposed to be a 19 pitch. What a difference in ride and fuel burn rate...

I just changed my 115 yamaha 4 stroke from a 19 pitch to a 17 pitch. MPH went up and boat responds better. My RPM's are still around 5200-5400 at wot. Any ideas?

gotta give me some more info here...no difference in rpm ?

New prop 13.25 x 17 old prop was a K19. New prop is aluminum. RPM was almost exactly the same with an occasional blip to 5400. Previous wot rpm was 5200. Boat is a 2001 194 Cobia C.C. From what I was reading I expected my RPM to go up at least 300-400 . I never measured the diameter of the K-19 so I dont know if the new prop is larger than the old one in that respect. The new prop is much lighter so even that should allow rpm's to go up. I have only had this boat for a couple of months.

I don't know a thing about mechanics but when i bought my f115 i was told wot was 5500-6000 rpm.

"occasional blip",what is that if i were you,i would verify the tach first,dropping 2" in pitch,should've given you approx 300rpm...dumb question,when the boat is on plane,the cavitation plates on the engine,are they above or below the water ?