I have a 14' G3 jon boat with 25 hp 2-stroke Yamaha outboard with stock prop (9 7/8 x 11 1/4) and a TSG jack plate. Looking to find out what's the best prop for this set-up. Any suggestions? Problem I'm having now is real bad cavitation.
If you are having cavitation problems then you have a couple options.
1. If you stick with your current prop then you need to lower the motor. I would go down in 1" increments until you stop cavitating. Its all right to cavitate some as your motor increases in RPMs but once you are fully on plane the prop should catch and you should be able to hit a good top speed.
2. Assuming you have a manual jack plate then get a prop with some cupping in it. What pitch is to recommend is a little more difficult. but 11 -12 is good start. Go with 11 and medium cupping or 12 with mild cupping. Drop by one pitch if you go with a four blade prop instead of 3 blades.
3. If you have an electric TSG and your goal is to run shallow then you can usually go with a little more pitch and cupping. The reason for this is that you will be able to jack up higher once you are on plane. The down side is that you lose some hole shot.
If you want to be more specific about what is the exact prop then you will need to install a tach for your motor. I run a 25 Yamaha 2 stroke too. With a powered jack plate I am able to run a 12 pitch prop with heavy cupping.
Are you cavitating with the jack plate all the way down?
What is the Transom height?
What length is your motor shaft?
What size Jack Plate?
Where is the cavitations plate compare to the bottom of the transom?
I just went thru this same issue and there is a fellow named Ron at The Prop Shop that is a sponsor on this site and he got me straightened out ASAP.
I told him what kind of boat I had and about the 25 Mercury and problems with horrible cavitation etc. and he sent me an incredible 4 blade prop that has a proprietary blade cup that holds the water unreal even with the motor trimmed all the way out and jacked up till the prop tips clear the water. It was kinda pricey and you could save $ by going with a similar 3 blader but if you want the best performance possible this is a no-brainer.
It may sound like I am pumping him but honestly don't even know Ron other than the recent transaction we had over the phone and he is very knowledgable about tweaking a boats performance.