Grady White 36' Express repowered with Yamaha 300 CV

[mbejot]

Hi,


I own a 2006 Grady White 36' Express and replaced the three Yamaha 250 CV for three Yamaha 300 CV.
Since I changed the engines, I have a vibration who starts at 2200 RPM and stops at 2600 RPM.
I talked several times to the dealer who changed the engines and they say that it must be because structural and flotation changes were made in 2008 on the hull.
My opinion is no boat should vibrate at any RPM, does anybody has changed engines on a Grady 36' Express prior to 2008 ?
And what is your opinion about this vibration ?

 

[ElyseM]

legit dealer do the work? props matched correctly?

 

[mbejot]

YEs a decaer did the work. Props are OK.

 

[family affair]

Does it always happen or is sporadic?

 

[ItalianAngler]

Hi,


I own a 2006 Grady White 36' Express and replaced the three Yamaha 250 CV for three Yamaha 300 CV.
Since I changed the engines, I have a vibration who starts at 2200 RPM and stops at 2600 RPM.
I talked several times to the dealer who changed the engines and they say that it must be because structural and flotation changes were made in 2008 on the hull.
My opinion is no boat should vibrate at any RPM, does anybody has changed engines on a Grady 36' Express prior to 2008 ?
And what is your opinion about this vibration ?

I have no experience with that boat and power setup, but.... a LOT of people on here have repowered with all kinds of different combos. My guess, there's an issue somewhere with one of those motors or how they are setup, and it's likely an issue that can be corrected once identified. I'd push them on this to find a solution, as I agree with you, it shouldn't vibrate.

 

[Halfhitch]

That's sounds like a harmonic vibration at that very specific RPM range. First of all, that dealer that gave you that BS line about it being because of a design change is full of crap. Forget them, if they will lie about that then you will never know if you can trust them about anything.

I am assuming here that you have installed two right-hand rotation units and one left-hand. I would start by removing the props, being sure to mark the two RH ones for which unit they were on. Then start them up on the muffs so you can raise them out of the water. Put them in gear and look for obvious wobble of the prop shafts. Then check to see that the prop shafts are rotating within Yamaha's run-out spec. with a dial indicator. If that checks out on all three, then switch the two props on the RH units and run the boat. Vibration still there? Then raise the center engine fully and run the boat on two engines. Vibration still there? Then try other combinations of engines to pinpoint the culprit. If you need help performing those things and your buddies aren't up to it then hire a mobile mechanic, don't use that dealer. Remember, they lie.

 

[ElyseM]

you said props "OK". the 2 outboard props should be the same pitch and diameter. the center prop will not be the same, i do not know what the correct numbers would be (and i wouldn't ask the dealer). once that is locked down, you may want to just pull the props and have them scanned to make sure they are to spec. if that is correct, then it's the troubleshooting above. good luck, ron