Thread: Will prop change help on 50hp Mercury

Move it up one bolt hole at a time. Easy way if you don’t have a floor jack. Let motor down. Crank trailer dolly down, put a block or 2 of wood under scab, loosen top 2 bolts and remove bottom 2. Then crank younger of trailer up an inch or 2 and see where your bottom bolt holes are. May have to play with it just a little but you will get the aligned. Then snug them up and go try it. May have to go up another hole but I’m thinking 1 should do it.

Sincere "thank you" to all you guys for helping me out. I will make suggested changes and report back asap.

Each hole is 1/2" I believe. You are 2.5" low so at least higher by 2 holes would be a good start. One hole won't do much for you IMO. You don't have to be exactly level with the bottom of the boat, that's just a starting point. You can be one hole one way or the other and improve performance.. its sort of a trial and error thing. 2.5" below the transom is definitely way too low though. You are also going to go up in RPM and you will not have to trim as much to raise the bow, so be aware of this... watch that tach so you don't over-rev that motor... it'll log when you over-rev it and merc doesn't like that! Your rev limiter won't kick in until 6300 ish, but you want that motor in the 5800 range.

Originally Posted by Kevin22

Each hole is 1/2" I believe. You are 2.5" low so at least higher by 2 holes would be a good start. One hole won't do much for you IMO. You don't have to be exactly level with the bottom of the boat, that's just a starting point. You can be one hole one way or the other and improve performance.. its sort of a trial and error thing. 2.5" below the transom is definitely way too low though. You are also going to go up in RPM and you will not have to trim as much to raise the bow, so be aware of this... watch that tach so you don't over-rev that motor... it'll log when you over-rev it and merc doesn't like that! Your rev limiter won't kick in until 6300 ish, but you want that motor in the 5800 range.

Thank you

The other guys beat me to it, but yes, that motor absolutely needs to come up. You will likely see a pretty significant rise in rpm’s, and might even be able to go up a pitch in prop and gain some more speed. I would go up at least two holes and go run it and see where you’re at, but I bet you may end up needing to go up 4 holes if there is a 1/2” gap between holes that the other poster mentioned (that sounds right in my foggy memory). That would get you a 1/2” low on the transom. I would guess that the motor will end up liking a 13p prop, and possibly even a 14p depending on RPM’s. I have a 14p Yamaha black stainless on my 1556 and it does well.

Moved motor up 2 holes and got to try it this morning. Gained almost 2mph (1.7) RPM was 6150/6200. Seemed to bite good at takeoff and had no issues turning sharply under power. What would you guys suggest for a new prop? Go to 13p and keep same diameter? 14p??

Thanks guys

I think you will for sure be fine with a 13p, and it might could even turn a 14. Your holeshot with be a tad worse going to a 14 but theoretically your top end should be better as long as it can get to the right RPM’s. Best option would be able to test and try both if you know anyone with some props you could borrow to try. I would keep the same diameter.

If your motor was indeed 2.5” low, you could probably still come up even more and gain some more RPM’s, which would allow you to run the 14p prop more effectively. Like I said in my previous post I’ve got a 14p on my 1556, although I would guess it’s a little lighter than your boat.

Originally Posted by DHC

I think you will for sure be fine with a 13p, and it might could even turn a 14. Your holeshot with be a tad worse going to a 14 but theoretically your top end should be better as long as it can get to the right RPM’s. Best option would be able to test and try both if you know anyone with some props you could borrow to try. I would keep the same diameter.

If your motor was indeed 2.5” low, you could probably still come up even more and gain some more RPM’s, which would allow you to run the 14p prop more effectively. Like I said in my previous post I’ve got a 14p on my 1556, although I would guess it’s a little lighter than your boat.

Thank you sir. I'll provide feedback once I get to try the props you suggested.