Pulsing Vibration

[Novation]

I recently noticed that I have a very slight "pulsing" vibration -- vacillating between no vibration and a very, very slight vibration. This occurs all within 1 second or so intervals. It only occurs while underway. I only noticed it on an extremely calm evening... with any chop you really have to be looking for it to feel it.

I looked under the boat at the props/struts to see if anything was noticable, but other than a slight nick on one of the port blades, I didn't see anything unusual. I checked the v-drive coupler bolts, the engine mounting bolts, transmission oil and the shaft seals and nothing was out of order.

Frankly, I don't know how long I've had this vibration and to my knowledge haven't hit anything. I was planning to have the props scanned at the end of this season before this issue came up, but I assume any prop vibration would be constant, not pulsating. Is this maybe a strut bearing going bad?

The dealer didn't have any ideas, but they are only going by my description of the problem and will look at it when I take it in.

Any ideas what it may be? Thanks....

The boat is a 2005 340 with 8.1s and v-drive.

 

[fwebster]

Have your wheels balanced and trued if you want to, but what you are describing is engines that are slightly out of sync. Sea Ray does a good job af adjusting the sync gauges, but things change over time. Just because the sync needle is centered doesn't mean the engines are at the same rpms........it only means they are close. If they are not very nearly the same then you get a harmonic vibration between the engines.

Next time you sense the pulsing, try increasing one or the other throttle very slightly....the pulsing wwill either get worse or go away

 

[Novation]

Thanks Frank. I'll try it out this weekend. I was going to have the props tuned up in any event this year.

 

[ImpulseIII]

"Pulsing Vibration" Sounds like the title of a porn movie :smt101 ....That said, I think Frank hit it right on the head.....oops.... :lol: Synchronization of the engines I mean.... :smt018

 

[Four Suns]

I think I read on the Sea Ray press release on the 47 DB that it is the feeling you get in the sky lounge.

 

[Asureyez]

A bearing to check ...

A worn cutless bearing will cause a vibration as you describe.

Do you run in really shallow sandy silty waters?

Have you run aground recently or been in a situation where you have blown a lot of sand around under your keel? (that nick)

If you grasp the prop and shake it side to side and up and down and there is any play, any, you can be gettign some whip from a worn cutless.

 

[Novation]

Thanks Chad -- I'll try to get under the boat this weekend to see if I feel any movement. I haven't hit bottom, but we sometimes anchor near shore and it's not unusual for sand to be kicked up while setting the anchor, etc.

I'm hoping Frank's is the answer, because a worn cutlass bearing sounds expensive (is it?) and it would probably cut my season off short (I planned on pulling the boat in a few weeks for the season, but if I have to pull it for this, it doesn't make sense to put in back in).

If it is one of the cutlass bearings, does it make sense to change both at the same time? I rather be proactive if it makes sense....

Thanks again.

 

[fwebster]

Chad has given you a possible reason for the pulsing vibration. On a 2 year old boat is in't a very probable one.

About the only way a cutlass bearing would wear on a boat as new as yours was if you have been in shallow water a lot and caused the bearing to run in a sandy/gritty enviornment. I would think you would have found crap in your strainers or had other problems from the sand/grit like worn sea water impellers long before a cutlass bearing failed. Having couplers out of alignemnt can also cause cutlass bearing wear, but you would have felt a constant vibration, not a pulsing one.

If you try to check the cutlass bearings in the water, bear in mind that it takes some force to move a shaft in a worn strut bearing. You aren't going to paddle under the boat and grab the prop with one hand and wiggle it. My boat is bigger, but to chack mine, I have to stand under the boat and raise up on the shaft with my shoulder to make it move.

This is one of those worries that is easy to over complicate........go out and play with your throttles. if you still get the pulsing, then lets move to step 2. But either way, you wouldn't replace the cutlass bearings until you hauled out for the winter anyway. Also, unless there are signs of wear, you don't replace the second cutlass bearing until you need to. Its not a bg expense...Bearing is about $100 plus a couple of hours yard labor.

 

[Novation]

Thanks Frank -- I intend to play around a little with the throttles this weekend.

You are right, of course, about trying to feel movement -- it's such a slight vibration I doubt (now that I'm thinking about it) that a trip under the boat would be worthwhile...

My brother-in-law is an auto mechanic and he was on the boat over the weekend. He said that in a car, a pulsating vibration usually means a bearing is going bad. I have no idea if that's true or not, but that's why Chad's comments about the cutlass bearings caught my attention, even for a relatively young boat (that is pretty well pampered)....

As always, I appreciate the feedback and will report back after some throttle time.

 

[bluebelly]

On three different boats I have noticed the the same pulsation you are describing. The three boats are a 340, 40, 44 sundancers, all with 8.1 horizons. I have put about 600 hours on these boats. The problem is caused by the "resonance set up" from the propellers loading water on the underside of the hull and its rudders and struts. The phonomenon is more pronounced in boats with solid fiberglass hulls and solid fiberglass stringers, which all of these boats have. What is happening is the stringers are acting like a "tuning fork" and are transferring the vibrations longitudnally along the hull. The pulsation comes and goes because the hull and the sum of its parts i.e. (engine, trans, shaft, prop, cutlass bearing, shaft log, rudder etc.) is trying to absorb these vibrations and when it cannot absorb anymore it then "releases" rapidly and the the process starts all over again, causing about 10 cycles per second. On my boat I notice it most when I am loaded light, as in 1/4 tank of fuel and 1/4 tank of water and no one on board. At first I thought it was the rudders oscilating under the thrust of the engines. Using a tool called a vibrometer, I took measurements of the rudder posts and discovered they were solid. After taking measurements of other parts of the engine and trans, I was standing on a stringer in the engine compartment and I could clearly feel the vibration under foot, all of this while under way of course. I believe the lack of wood or solid core of some type in the stringers is mostly to blame. Lengthy discussions with Sea Ray confirmed this.


Hope this helps.

 

[Novation]

Thanks Bluebelly, I appreciate the information.

I'm treating this as a "new" occurence, but frankly, it is slight enough that I may have simply not noticed it before. A couple of passengers commented about it (and that never happened before), so I am assuming this is a new issue.

I'll play around a little this weekend and try to see what I can find out.

 

[bluebelly]

One other item I forgot to mention is to make sure your canvas top is not the source of the vibration. As you can imagine it can create alot of force against the radar arch while underway.

 

[Novation]

Well, I think I've found the source of this problem and wanted to give a quick update. I had the props pulled this week to be "tuned" up, hoping this was the source of the vibration. Today, I went to the boat to start waxing etc. for the new season. Since the props are off, I took a look at the port cutlass bearing -- I thought the vibration seemed to originate on the port side. Fortunately, it looked fine. The starboard custlass bearing, much to my surprise, showed deterioration and actually looked brittle. I could even move the shaft a fraction when I pushed up on it -- unlike the port shaft which was solid and wouldn't budge.

I'll talk to the dealer tomorrow about replacing the bearing. Any ideas of what the approximate cost would be and should I have him replace both?