19' 1995 larson with 112 Johnson spl

[Shwinkyyy]

hello everyone, I just bought this boat mentioned on subject line. The current prop is usable but chewed up a little on the edges so I would like to replace it. Im not looking for anything specific out of a prop. Just a good standard range to generally enjoy the boat. The prop on it now pushed the boat about 30 mph at WOT and the tach read 4,000 rpm (not sure how accurate that is) a guide i looked up said recommended range is 5,000. so any recommendations on diameter and pitch would be very appreciated.

side note, I have no idea what the specs are on current prop at this time.

 

[Texasmark]

From the go-fast prop slip calculator, assuming your 112 HP is a 2:1 gear ratio, as I see most engines in that general range...100-125 hp, and you said you want 5000 rpm, and assuming the the Larson isn't too heavy, nor do you plan to load it heavily, has a good planing hull....looking at prop slip calculation number here, go-fast says that for a slip of 10% (a reasonable number for what I said) gives you a pitch of 17, diameter in the 13+" category, I think OMC is 15 spline.

If your current prop is actually 17 and your slip was 10% and you were really at 4000 you'd be at 29 mph....a little less slip would get your 30 mph.....close enough for a SWAG. So the question is, is your engine at 100%? Is the setup at 100%? Are your instruments accurate? If all that is a yes, you need to drop down to 14P aluminum general purpose. If not available a 15P to have your same speed and get your desired rpms. I think something isn't telling you the truth or your boat is really heavy, or a deep V.

 

[Shwinkyyy]

Ok thank you so much that was very helpful.

 

[Shwinkyyy]

Just wanted to leave an update. The recommended prop worked perfectly! I went out with some buddies today even with a lot of weight in the boat she went 31mph and my tach gets wierd after 4,000 but it definitely felt and sounded like she was at that 5,000 range. Thank you so much for the help she is running perfect because of it.

 

[Texasmark]

So which pitch did you buy?