I bought a speedboat in january and am relatively new to boating.. The engine is a 135hp mariner v6, i took the boat out yesterday for the first time and found that i had major problems, the boat when at full throttle was revving its head off but going nowhere, i could not even get it up on the plane..the speedo was not reading but i would say the boat wasnt passing 15mph.. I have little knowledge of outboards but to me it was as if the prop was just not giving enough thrust (too small maybe?) Measuring the prop with a tape when i got home it appears to be a 13 diameter by 19 pitch.. Is this inadequate for the engine?? or am i barking up the wrong tree?? Any help appreciated