Sorry if this has been asked before but I searched and can't find it.

I recently bought a boat with a 45 horse mariner. It came with two four blade props. One has 12p on it and one has 13p. Can anyone tell me what these numbers mean.

Thanks in advance.

common question, if you do a google search, you will get the answer in all of about 15 seconds.

Prop pitch is the distance the prop will move forward with one revolution if there were no slip (think a screw turning into wood). Going up one inch in pitch, you'll lose about 200 rpms. The smaller prop will give you better hole shot and lower top end while the larger prop will give you worse hole shot but better top end. You'll have to experiment with how big of a difference there is and which one you like better.