? Decoding prop and performance issue

[sweebs]

Hello, I was last on here soliciting advice on my quest to get a boat with seized engine going again, well it goes!

My prop question has to do with what I have now. And the performance question is based on what the diameter and pitch is, does it make sense that I'm topping out at 6000 rpm or does this indicate a faulty tach?

The prop is aluminum and stamped on the hub with: "M2246" and as measured, the diameter of the 3 blade prop is 14"

The boat is a 1991 20 ft Thompson Calais sterndrive with a 4.3 and Mercruiser Alpha 1 Gen 2 outdrive.

My engine wot rpms are so far off spec I was assuming the tach to be out of calibration (I brought boatarama back to life after an 8+ year storage), but maybe the previous owner simply pitched it for pulling power?

 

[bruceb58]

You need to check out your tach. Look at the back of the tach and make sure its not set to the 4 cylinder position. If it's not, get a shop tach to see what it is really spinning.

 

[sweebs]

Anyone know what the stamping means? M2246

 

[Chris1956]

Do a search on that prop number. Maybe it will pop up and you can find the brand and pitch. Also, do a search on your outdrive by year to get the gear ration. Make sure your tach is for a sterndrive and set to count a 6 cylinder RPM properly. 6000RPM is way too high for that iron monster.

Normally you would want a 19P prop, for your boat and outdrive. However, that prop is only a starting point, and the proper pitch could be +- 2"" pitch.

 

[sweebs]

I had initially searched for that prop # and came up empty. Local boat shop thinks someone repitched and stamped that #... they assume my tach is bad and of course they just happened to have one for 100 bills

 

[SkaterRace]

That is not a bad price for one, I have seen them from $60-150. I would suspect a 19 or a 21 would be the best for your boat but need to solve the tach first.