[iceman49]

My dad has an 18.25 foot 2006 ranger fisherman tiller with 90 horse yamaha. The engine vibrates very badly at very low rpms and we like to troll and backtroll so this is a problem. The motor has a four blade mercury trophy plus prop (stainless steel, 17 pitch). We took it to the shop and they said it was the prop. I was wondering if a three blade yamaha alluminum prop would solve the problem. If anyone has a 618T please let me know if you have had similar issues. Or if anyone has a similar boat or similar problems or any input at all it would be greatly appreciated.

 

[ffishman]

If there is something wrong with the SS, then yea, a brand new AL should solve your problems. If the SS is brand new, never been reworked, or worked on, then you may have other problems. Why don't you just have the prop shop fix the SS so its good to go?

 

[JDSPINNERS]

Your description of "very rough" would tell me that your prop should show some extensive visible damage. I've bent blades completely over and at an idle could feel very little but anything over idle or attempting to accelerate it became very obvious. If your idling rough but have no symptoms at higher rpm's, then it's most likely not the prop.

 

[KP]

I believe it's common for there to be some vibration at trolling speed with some stainless props. It's especially noticeable with a tiller motor. Switching to an aluminum prop should resolve the problem.

 

[iceman49]

Thanks for all the input guys.

KP, is the trolling vibration for SS props because it does not have any flex?

 

[KP]

I don't know for sure but I think it has more to do with the weight of a stainless prop and the increased blade cupping associated with most stainless props.

I never had any vibration trolling with an aluminum prop. When I switched to a stainless Rapture prop (really heavy sucker) I noticed some vibration. Then I tried a Ballistic stainless prop that is lighter due to thinner blades and less blade mass. The vibrations almost disappeared. I had the Rapture checked by a prop shop to see if it was bent and they said it was almost perfect. They blueprinted it and I tried it again. Vibration was still there. Then I read on another site that it had to do with weight. I don't question that after my experimenting.

 

[dncncwboy56]

Spin your prop (on the motor) by hand and see if it travels in an elliptical motion, you could have either a bent main shaft or bad bearings in the lower unit.