Newbie Prop Question

[Buster_boy]

I have a 2001 Johnson 40hp 2Cycle twin on a 16ft Sylvan pontoon 2 1/2 toon. The prop reads 12x11c. First, what is the 'c' and second, why can I not find those dimensions anywhere? The prop finder here on iboats lists 11 pitch but not 12 dia, and 12 dia but no 11 pitch. Cabela's lists a Solas 12x17 but that seems a bit high (but if it works I guess its ok). How do I find a proper replacement? Maybe even one with a bit more 'Ooomf" to it?

 

[Starcraft5834]

12x11 means 12 dia, and 11 degrees of pitch... hard to say whether or not the prop you are looking to replace is correct for your set up,, if you are happy with the performance of your current prop, check prop replacement guide for your 40hp motor and pick one.. the correct prop for any given motor and boat set up may vary based on performance you are getting... ie- a prop with to much pitch is indicative with boats that wont get on plane and struggle, plowing through the water far to long... every engine, outboard or stern drive has a recommended WOT rpm range... that is rpm's at wide open throttle... the prop pitch that runs a boat within the accepted range is generally considered correct... conversely, a prop with to little pitch will over-rev the engine and cause it to run beyond the recommended rpm range, hence engine damage would likely happen... the more blades you have, the more thrust you will achieve.. 4-5 blade props are best for heavy boats or for heavier boats with under powered engines..

 

[Sea Rider]

Need to tach that prop with an induction tach as currently loaded on flat calm no wind water cond and check if inside its factory min-max wot rpm range, being an old OB, probably just very few props to play with.

Happy Boating

 

[Silvertip]

12x11 means 12 dia, and 11 degrees of pitch... hard to say whether or not the prop you are looking to replace is correct for your set up,, if you are happy with the performance of your current prop, check prop replacement guide for your 40hp motor and pick one.. the correct prop for any given motor and boat set up may vary based on performance you are getting... ie- a prop with to much pitch is indicative with boats that wont get on plane and struggle, plowing through the water far to long... every engine, outboard or stern drive has a recommended WOT rpm range... that is rpm's at wide open throttle... the prop pitch that runs a boat within the accepted range is generally considered correct... conversely, a prop with to little pitch will over-rev the engine and cause it to run beyond the recommended rpm range, hence engine damage would likely happen... the more blades you have, the more thrust you will achieve.. 4-5 blade props are best for heavy boats or for heavier boats with under powered engines..

12x11 means 12 inches in diameter but NOT 11 degrees of pitch. It means 11 INCHES of pitch. That number means for every revolution of the prop the boat would move forward 11 inches -- ignoring the slip factor.

 

[Silvertip]

You do not want a 17P prop as that would drastically "lug" your engine and the boat would be a complete slug. What do you mean by more "oomph". If it is speed you are after that's one thing. If you want hole shot (get up to speed more quickly) then that's another. Neither question can be answered unless you know what the wide open throttle rpm and speed is with the current prop. You cannot guess with choosing a prop. Numbers are important. What you have is probably pretty close to what you need. An 11x12 or a 12x11 will likely perform fairly close to each other with preference going to the 12x11. Also look for a pontoon-specific prop which has big rounded blades. You also need to select a prop that puts the engine at its recommended WOT rpm with what you consider an average load.