Vibration

[earthmover17]

1999 Sea Ray sedan bridge. I have developed a vibration that you can feel all the way up to the flybridge. It happens from about 1750 to 1950 RPM and gets less after a couple of hours.
I just had it out and had the shafts,props and cutlass bearings checked with results of no problems. It's CAT 3196 powered with CAT gears. My next step is to check the alignment of the shaft flange to the gear flange. Has any one had a similar issue?
Any thoughts would be helpfull.
Thanks:smt101

 

[fwebster]

I think you are on the right track. A vibration that comes and goes is going to be hard to find unless it is due to shaft flex and misaligned couplers.

If that doesn't solve your problem, the next thing I would do is to remove the shafts and have a machine shop put them on a lathe and check the runout at both ends, and get the couplers refaced and trued at the same time.

Let us know what the outcome is..................

 

[geriksen]

can you tell which side it is on?
at speed pull one throttle back a bit and see which side changes the frequency of the vibration
how did they check the props?
did they do an engine alingment while the boat was in the water?

I also would like to know what you end up finding.

do you have a spare set of props?

 

[earthmover17]

Thanks for the replies. I will keep you informed of what I find out. The starboard prop shaft turned kind of hard so I realigned the couplers. I took it out for a sea trial and did exactly what geriksen said. Results were I now think it's the port side.
This is going to be one of those problems I chase for a while.
When I had the boat out the shafts were checked with a dial indicater and the props I don't know but the guy who did the bottom(30 years experiance) said he did'nt think it warranted pulling them and sending them to the prop shop. After more checking the vibration starts at about 1500 rpm and stays all the way to full throttle. I am going to get a second opinion from a local mechanic next week.
Jack

 

[Lake Erie Boater]

Please don't quote me on this, but I believe the PropScan people will check them (the props) at no charge (at least they do so here). Check their website at www.props.com and click on PropScan Shops to see if one of their dealers is close to you. Call them and see if they offer the same initial no cost service. Of coarse if repairs are necessary, then they dig into your pocket book.

 

[fwebster]

I thought you sad the props were checked or this is where I would have suggested you begin.............

If the 30 year guy eye-balled the props, that is where I'd start. Pull them off the boat and take them to a prop shop and have them trued and balanced. Your symptoms sound exactly like those one would expect when one blade is blightly bent. The wheels on a 480DB are large enough that even a little our of true is going to be noticable.

On modern boats where the transmission is used to get counter-rotation, one gear turns in one direction (reverse) and the other in the opposite direction or forward. The number of clutch plates are different in forward than in reverse, so it is normal for one transmission to be harder to turn than the other.

And just so we covered it, the boat needs to rest on her own bottom in the water for several days after a haul-out before you try to realign the shafts.

 

[geriksen]

ditto

looking at the props is not checking them
if you have access to a propscan type service, that would be well worth the $$
I have had bad new props and bad props straight from the prop shop
when I send -em back they never find anything wrong but somehow they run smooth when they return. ;-)
I use a propeller shop that is "old school" but they do very good work however......
If there was a shop with a propscan system I would prefer that.

I would have that done if everything else looks ok
or borrow another set of wheels to to see.....

 

[earthmover17]

Guys once again I appreciate the help. I was out today with a mechanic who helped me realign the gear coupler to the shaft coupler. It was out about .020. I will sea trial it wednesday.
I am still skeptical though cause the prop shaft still turns rather hard. I am starting to lean towards something underwater(prop,shaft or cutlass bearing). I have a sneaky suspicion it will have to come out to see exactly whats going on.
fwebster Thanks,As you said one gear turns in reverse as both engines turn the same direction. That is the reason the gear that turns oppisite of the engine makes more noise when you put it in gear.

 

[fwebster]

You may be chasing more than one contributor to the vibration. But, it is like concentric circles, keep working on it and each circle gets smaller easier to handle and identify. Then sooner or later you get to the center and hit the bulls eye.

I will tell you that a coupler out by .020" is 5 or more times what is considered acceptable and can certainly cause a shaft to deflect. When you rotate a shaft that is deflected but bolted down on the coupler end, the opposite end....the one with the prop on it.....tends to whip. In essence a deflected shaft has run-out forced into it and run-out is going to shake it you spin it fast enough with enough torque. A 3196 turning 24" wheels will shake if the shaft has run-out.

 

[earthmover17]

We sea trialed the boat today and the vibration was less. It seems as though the port engine also needs alignment as it still has vibration when the starboard engine is throttled back.
The twin disc trannys I have call for 40 weight motor oil(funny they call it motor oil beings it goes in an engine) is this regular straight 40 oil or non detergent.
Jack