Logo
FULL SITE MENU

Vibration

D

DP1

New member
Twin 454cu in inboards.While underway should there be any vibration?How do you gauge a little versus a lot.I have read where some is normal,some is not,but what is some?I feel a bit,nothing shaking,or coming loose.
Thanks
DP1
 
ALL inboard vibrate! The shock wave off the props slam against the hull to make noise and vibration. Can't avoid it. One of the advantages of outdrives--the shock wave passes by the cavitation plate so they don't see that.

Jeff
 
When we first got our 34C Silverton, there was a noticeable shimmy vibration felt by standing in the back cockpit. Other boats I had been on over the years were vibrators but not with the "shimmy" . Higher RPM made if worse and anything below 1500 or so was fine but THAT was only about 5 knots or so. After propscan, it solved our problem as it was really just props out of "balance". The graphs before and after made it look as if the original set up was dropped on the floor and the graphs looked like a silouette of the alps. The end results were as if the bars on the graphs were drawn with a ruler...literally perfect.

I would believe if you have shaft or cutlass issues, you will need to look into this with greater time and detail. I was quite impressed by the difference
 
Well, That is True, Jeff. We also kept our 26' Bayliner for 2 years while we ran the Silverton and the outdrive on it was SMOOTH. It was the difference between the BAD props and the TUNED props that made the difference such a big deal. I also wonder if the diameter of the props had a thing or two to do with the vibrations. The outdrive prop was 14" and the inboards were 18". One was stainless the other nibral.

Regardless....Propscan made a HUGE difference AND as careful as we are, there is NO WATER in the NJ bays so on our way out to the deep water, you never know when your going to bump something and screw up that beautiful balance $$$
 
Last edited:
Does this come in at a given RPM? Can you isolate it by shutting one engine down? Have the props and shafts ever been checked? How are the cutlass bearings? Are the engines aligned? How are the motor mounts? Are the engines running smooth, or does one have a misfire or dead hole? Are the exhaust hoses/mufflers isolated or are they telegraphing against the hull or deck? DP1, you have a post concerning moving your starboard engine to port, how did that work out for you? Was that related to this vibration? Or as an attempt to align the engine to solve it?
 
Last edited:
Bob
Noticed Vibe around 1600 rpm*which is a nice*8mph for us.Notice it at higher rpm also.Before doing any adjustments I ran each engine by itself to 1600 rpm,port side very smooth,starboard some vibe.Engines run smooth no matter what rpm,props were*suppose to be new 3-4 years ago when we bought the boat and to date no dings or chips,cutlass bearings good,have not checked shafts.Engine mounts in good shape.Then I checked alignment,starboard needed to move to port which I did,now runs smoother,when checking the gap stayed the same all when rotating shaft always a gap on left side of couplers.Still get some vibe*when running both above 1400,seems smoother around 2000 to 2200.Then notice above that again.Notice the vibe around the cockpit,nowhere else.Do not have a syncronizer so I used a laser tach and found both to running within 15rpm of each other@ 1600rpm
Regards
DP1
 
I have found that NEW props are no guarantee that they are within tolerance for vibration free operation. As for syncronizer, you can feal the beat frequency of the engines as the rpm iincreases and you can hear the sync as well. If you are within 15 rpm (?) that is some tight match. I find my "sync" is fine within 100. It sounds as though you may have a shaft alignment and prop issue ... The events as you describe them is what I had dealt with 5-6 years ago and it was the props. I hate to admit it but that $400 expense for tuning was SO WELL WORTH IT and in my case, I know it is something I probably need to do again. I have several other things that 400 bucks would work for but the end result of that propscan is worth every dollar
 
DP1,

Interesting, "always a gap on the left side of couplers". Meaning the front of the engine is pointing off to the right?

The new props 3-4 years ago may add a little history to the cause of this, if she didn't leave the builder this way.
 
Sorry,meant the gap was always on the right,so I moved the engine to the left.Will check a few more things this weekend.
DP1
 
Back
Top