Prop help.

[kerryd15]

I have a merc 50hp 3 cylinder 2 stroke on a 89 16ft side consel boat. The motor has a 3 blade black max prop, 13 pitch 10 3/8 diameter. The prop has some dings from the previous owner and I believe is not balanced anymore. There is a wear spot on one side of the prop where the prop fits into the lower unit. I installed a tinytac and at wide open get roughly 4800RPM. The motor should be 5000 to 5500RPM max. I have been playing with the idea of going to a 4 blade prop. Any comments or suggestions as to what would work. I think I would need to go to a 12 pitch. Not sure how the 4th blade would affect things.

[CAMAN]

I'm not very knowledgeable with 3vs4 blade props on a lower hp motor like that. But the uneven wear concerns me and I would suggest getting your prop shaft checked to ensure it's not bent, that would explain the vibrations it sounds like you're experiencing. Small dings rarely throw a prop out of balance unless they chip material off.

[magnum mike]

Take the boat to a reputable prop repair center. Have the prop & shaft checked. As far as a 4 blade prop, the 50 hp is too small to gain the benefits of the 4 blade screw.

[Whoaru99]

I have a merc 50hp 3 cylinder 2 stroke on a 89 16ft side consel boat. The motor has a 3 blade black max prop, 13 pitch 10 3/8 diameter. The prop has some dings from the previous owner and I believe is not balanced anymore. There is a wear spot on one side of the prop where the prop fits into the lower unit. I installed a tinytac and at wide open get roughly 4800RPM. The motor should be 5000 to 5500RPM max. I have been playing with the idea of going to a 4 blade prop. Any comments or suggestions as to what would work. I think I would need to go to a 12 pitch. Not sure how the 4th blade would affect things.

Mercury's rule of thumb is that 1" change in prop pitch changes engine RPM by 150-200 RPM, and generally recommend going toward the high side of the range with your normal load.

Merc Prop selector tool. Generically using a 16-ft boat, I came up with 13" prop. http://www.mercurymarine.com/propellers/prop-selector/#

Before you go on with the prop, I'd ensure the motor is achieving full throttle, in proper tune, etc. Unless that boat and or your load is/are exceptionally big/heavy for 16-ft the standard props are usually right.

[Surface Tension]

Take the prop off, put the muffs on and run the outboard in gear. Check the prop shaft to be sure if its running true. When your done you might as well winterize the outboard.

Bring or ship the prop to a prop shop(can't go wrong with Sodderblooms)and have it fixed.

Now give it a try and check your RPMs.

[Black_Bay]

Get a 12 pitch Mercury Spitfire or Quicksilver Nemesis Prop. They are 4 blade props with smaller diameters. http://www.mercurymarine.com/propellers/aluminum/spitfire/

[kerryd15]

There are some 1/4 inch deep chunks missing from the blades. I am not getting vibration when running. Does it pay to fix something like that? I have gone thru all the linkage and timing per the manual and believe they are correct.

[harvey lee]

Take the prop off, put the muffs on and run the outboard in gear. Check the prop shaft to be sure if its running true. When your done you might as well winterize the outboard.

Bring or ship the prop to a prop shop(can't go wrong with Sodderblooms)and have it fixed.

Now give it a try and check your RPMs.

+1. Only way your going to be able to tell if this is the motor or the prop.Yopu cannot go wrong having Jay at Sodderbloom's check the prop. Jay helped me with a prop size issue and my boat has never been the same, awesome and very helpfull person.

[Surface Tension]

Your baseline is 4800 RPMs with a dinged up 13 pitch prop.

Before buying a new prop with different pitch you have to know what you have with a good 13 pitch prop. The wear mark on the prop, that could also be addressed at the shop.

Could be the hub is off center, bent prop shaft, or bent prop.

So what I'm getting at is you don't know what your RPMs are with a 13" pitch prop.