Bad vibration

definetely you bent something, sometimes is not visible, but it doesn't take much to make the boat shake....
I'd suggest pulling prop and shaft and have them checked...

check your exhaust hose. CC made some wonderfully sharp "S" bends for our Martinique and the previous owner over heat the exhaust. and under the floor the hose for each side was kinked. The right side specially. so bad the engine refused to run from 750-1200 rpm. it would literally hop in rpm's. And during of which it would start to vibrate violently.

I had a similar experience - hit a submerged log (it floated up so we did see that) - the prop was undamaged, believe it or not.    However, the shaft got a .010 inch bow put into it.    We straightened it ourselves using homemade V blocks & a dial indicator. We got it to about .0015 of true (using homemade V blocks & a basement floor for a surface plate!).    No vibration now.

Just started looking at things under the boat. Not a scratch on the prop which is not conclusive of a bent shaft, but did notice that the rudder is really loose. It wiggles back and forth, port to starboard, about 1/4 to 1/2 inch. Cannot imagine that this is within spec nor do I even know what that is.   Searched to forum and did not see anything specific on rudder tightness.   Anyone got any ideas. Thanks Rob

It is definitely side to side. I can shake is back and forth. It moves so much that it goes clunk clunk

So it is a radial play in the rudder shaft and not lateral in the port! I do not feel you understood my question. I would say that the tiller arm is loose on the rudder shaft. If you don't understand "tiller arm", think small sailboat.
Take pictures and post them.

The tiller was secure to the rudder. The shaft was loose in the port. The rudder shaft was sitting low in the port and wiggling all around. Adjusted the nut on the dry side and it raised the shaft in the port which stopped it from wiggling. I watched the video to determine run out, but I do not have a gauge. We rigged up a ghetto gauge with some clamps and a fine tipped pointed rod. There was not noticeable run out at all. This is not surgical, but this is not a small vibration either, so if it is not fixed I will have to try to find a gauge somewhere where we can get accurate measurements. I am not holding out much hope for the loose rudder, but we will see. I will post results

If it’s vibrating that bad you may have a bigger issue than a bent shaft. Usually you won’t feel that big of a vibration just above idle I would think. It may be in your tranny if you can’t see any obvious problems with your shaft. Just guessing though.    

I'm sure your right, I have worked on alot of tranny's on old muscle car have seen a bad output shaft cause a heck of a vibration and still able to move. I know,I know this is not an old muscle car.

Eric - how's the new job going? Have you been working on towboats that have grounded due to low water?

How would I isolate to eliminate this as a possible problem? Thanks Rob

RMG001 wrote: I checked the run out at the brace back to the prop.

What's the "brace"? Do you mean the strut?

RMG001 wrote: There is no play at all in the shaft due to a worn cutlass bearing.

If the cutlass is worn, then you should have play in the shaft to the bearing. The exception is if the shaft is bent inside the cutlass bearing.

RMG001 wrote: I will try to rig something up today to check run out above the strut.

You need to pull the prop and as mentioned check the run out at the prop taper.

RMG001 wrote: It was either something catastrophic in the engine or trans. or we hit something. It was a noise and then vibration. I should have run the engine in neutral to eliminate a source I can do that today in the driveway. Thanks for everyone's input.   Will keep updating till the end of the issue

Water and soap the cutlass bearing so you can run the engine and put it in gear. Check the shaft first so you don't possibly do more damage.

The rudder probably did not ever just drop it appears to be adjustable up and down by what I will call the packing fitting and lock nut. It is threaded on the port. Moving the fitting a couple of turns took the slop out. Maybe I did something wrong here, but it worked.   Let me know if I am going to get in trouble. I am about to go out and get it set up to run in the driveway.   "Brace" was meant to reference the strut. Thanks for the soap and water on the cutlass bearing I was thinking that would be bad to run dry. I will pull the prop and check at the end of the shaft

Like was suggested earlier I probably need to take a picture and label the components so we are on the same page.   I am reading all of the posts and appreciate everyone's help. It is a vocabulary issue as much as anything right now. I will try to get the correct terminology so we can be more clear on future posts. Thanks Rob

Rob,
I have to ask, are you looking for more answers? You've been on site at least 15 times this afternoon!

I really don't know what could be added to what has already been said. Plus, you may have noticed that Eric even commented. If you don't know him, he has gone on to other big boat repairs but still has a "hand" in Fantastic Finish Marine. They are the premiere marine trans rebuilders in the country. Eric has been a member here for years, has helped many and has rebuilt many of our transmissions.

We are waiting on you to take off the prop and check that shaft. Don't forget to get that prop to the prop shop ether.