Re: 2013 sylvan prop size??
Step one is to optimize the setup before throwing money at props. Step two and three are to verify the accuracy of the tach and if you are using a pitot speedometer for speed data you need to use a GPS. If the prop is losing bite, lower the engine on the transom (that does not mean trim). You remove the mounting bolts and move the motor full down so the transom bracket sits right on the transom. Engines on pontoons run in very turbulent water so on those boats, deeper is better. Trim on a pontoon does not provide the same level of performance gain as it does on a V-hull. Getting the nose a tad high is about as good as it gets to 1/4 trim is probably the useful range. While lowering the engine will not likely increase speed, it will take care of the ventilation problem. Now make some wide open throttle runs with what you consider an average load and prop for that load. If you prop for a light load, performance may be fine but it will lug the engine when you add people or attempt towing water toys. We also don't know if this engine is a two stroke or four stroke so you need to look at the decal on the side of the engine to see what the RECOMMENDED wot rpm is. You then compare that number with your OBSERVED rpm and the difference is what you need to prop for. 2-inches of pitch up or down = 400 rpm (roughly). So the difference between 4800 and 5800 is 1000 rpm which means you need about 5-inches less pitch. However, because the engine being severely "lugged", even a 2-inch pitch change may enable the engine to get "over the hump" so to speak and pick up speed and rpm in the process. So prop selection is a crap shoot and when rpm difference is as great as yours, it becomes even more of a challenge to get it right -- the first time. My suggestion would be to work with a dealer to see if they will let you try a couple different props. Then be a sport and buy from them.
