I have (2) props for my new Yamaha 25 HP 4 stroke and I am considering the purchase of a third prop. The motor is mounted to a 14' Express aluminum boat (flat bottom, center console). WOT for the engine is 5,500 - 6,000 rpm (per the manual).<br /><br />(1) OEM Aluminum: 9-7/8 x 10-1/2<br /> <br />(2) SST: 9 x 13 supposedly re-pitched to 11 but I doubt it.<br /> <br />(3) Proposed New SST: 10-1/2" x 11"<br /><br />The aluminum prop allows the engine to achieve 6,000 RPM at WOT but is not durable enough for salt water use. The new motor came with the SST prop noted in item 2. I recently had it repitched because the engine would not rev beyond 4,900 - 5,000 rpm with this prop. It took forever to plane out no matter how it was trimmed. I had the prop re-pitched to 11 degrees however I have my doubts that they were able to reduce the pitch that much. The WOT RPM for the engine is now 5,300 rpm and it still takes a very long time to get up on plane.<br /><br />Prop number three is the lowest pitch SST prop that I have been able to find. The diameter is 5/8" greater than the aluminum prop and a full 1-1/2" greater for the existing SST prop that I have. I have found a lot of informtion about pitch and how it affects hole shot and WOT but nothing on how diameter affects either of these. Can someone shed some light on this topic?<br /><br />Specifically- How, if at all, is the increased diameter of the prop listed in the third option going to affect performance.<br /><br />BTW- Both of the props that I currently run give me between 23 and 25 mph top speed. I suspect that for my boat configuration (and passengers) that speed is a function of the horsepower of the motor and that no prop change is going to give me more speed. Is that a correct assumption?<br /><br />The motor that I replaced was an old 35HP long shaft OMC. It was a motor that was built for the Navy Seals. My best guess is that the water pump gave up the ghost sometime during a trip my daughter and I took to Matagorda's East Bay. I didn't "figure it out" until we were about two miles into the bay from the 3 mile cut 
My daughter (17) looked at me and then the motor pouring smoke as we drifted to a stop and said "Dad!!! What are we going to do???" I baited up a line and cast it out and said "Can't do much else but fish at this point. Better toss that anchor out before we drift even further away from the cut" We ended up catching two nice reds and a bunch of "trash" fish that were fun to catch. A buddy of mine towed me in after he got off work.<br /><br />I miss that old, oil spewing 35. We could run 32kts (not mph... knots) WOT and cruise easily at 28 kts. On the other hand... it's nice starting with a key and having my battery charged while I'm running.
My daughter (17) looked at me and then the motor pouring smoke as we drifted to a stop and said "Dad!!! What are we going to do???" I baited up a line and cast it out and said "Can't do much else but fish at this point. Better toss that anchor out before we drift even further away from the cut" We ended up catching two nice reds and a bunch of "trash" fish that were fun to catch. A buddy of mine towed me in after he got off work.<br /><br />I miss that old, oil spewing 35. We could run 32kts (not mph... knots) WOT and cruise easily at 28 kts. On the other hand... it's nice starting with a key and having my battery charged while I'm running.