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Old 11-04-2011, 07:48 AM
jkski jkski is offline
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Steering vibration issue...any thoughts?

Roughly 3 months ago I had an incident with my prop that resulted in the rudder being slammed to the side breaking the steering clevis bolt. This unfortunately happened at roughly 40mph with a footer in tow and nobody was injured but you can imagine the force that was against the rudder.

The boat is an 08 PS197 w/MCX and gear reduction tranny.
So, with the help of Eric from OJ, we put a new prop on the boat, a 13x14.5 which replaced the 13.7x15 that was previously on there. The 13.7x15 was what the TT boats were running back in 08 from what I recall and the newer 13x14.5 is what they changed to.

OK, so the problem is that with the 13x14.5 on the boat I get a vibration/shudder back thru the steering wheel at or above roughly 4000rpm's. The shudder is the exact same as if you were power loading your boat on the trailer. The problem goes away if I make a slight left or right hand turn but is very prominent if simply driving straight. My dealer, who replaced the clevis bolt, has re-checked everything to make certain the steering is OK and Eric was kind enough to send me another 13x14.5 prop to test so that I could put my own mind to rest that it may be a prop issue, and the issue persists.

So, my guess is that the new prop is causing some sort of additional cavitation at the higher RPM range that my previous prop was not but I am curious to know if any of the TT guys or people with the same set-up running the 13x14.5 experience this issue as you approach WOT? I can start to feel a slight hint of this at 3680rpm but it does not become pronounced until you are in the 4k range.

I absolutely love the new prop from Eric as it give a better holeshot and more top end (+3 or 4 mph) however, the vibration issue concerns me and I would think that it would lead to further issues down the road if I continue to run it.

I am open to thoughts.
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  #2  
Old 11-04-2011, 08:12 AM
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Things to check/recheck since the vibration is still there with 2 different props:

-prop shaft bent? check with dial indicator
-engine alignment?
-bent strut?
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Old 11-04-2011, 08:25 AM
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willyt willyt is offline
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I'd put my money on a bent shaft... How easy is the prop to turn by hand?
Could be that all 3 need work/replaced.
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Old 11-04-2011, 09:12 AM
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Can you tell us more about the incident?

Did you change out the rudder? Was the rudder port damaged?
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Old 11-04-2011, 09:19 AM
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vision vision is offline
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I vote for slight rudder bend since it occurs predominately within a certain speed range.
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Old 11-04-2011, 12:25 PM
jkski jkski is offline
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All good thoughts but all pose the same question: If the rudder, strut or shaft were bent, wouldn't the vibration exist at all speeds and be present regardless of which way the wheel is turned?

The incident was that a blade came off of the 4-blade prop while going 40+mph which resulted in the a massive imbalance of water eing thrust back against the rudder snapping the clevis bolt and throwing the boat into a right-hand powerturn. Fortunately we were in the middle of a smooth lake and pulled the throttle back immediately, and nobody was hurt.
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Old 11-04-2011, 12:36 PM
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Bouyhead Bouyhead is offline
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I'm with vision on this one. Our clubs new LXi had a very distinct whine @ 36 MPH, sounded like the tranny was going to blow. After some changing of parts buy the dealer it was a slightly bent tracking fin.
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Old 11-04-2011, 12:51 PM
jkski jkski is offline
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I should also mention that we did not hit anything and that there was no damage done to anything else, just a clean break and fortunately the blade must have gone straight down to the bottom of the lake.

The vibration is exactly what you feel when power loading, which I have always associated with cavitation.
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Old 11-04-2011, 01:12 PM
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Quote:
Originally Posted by Jerseydave View Post
Things to check/recheck since the vibration is still there with 2 different props:

-prop shaft bent? check with dial indicator
-engine alignment?
-bent strut?
Checking all of the above is all labor time so why not do it?
I would remove the rudder and have it checked to see if it's bent. You may be able to do this with a straight edge or have your MC dealer check it for you.
Borrow a dial indicator and rotate the shaft to see if it has any runout.
Use a feeler guage at the coupling and check to see if the engine is out of alignment.

I would bet at least one of these 3 items is out of spec since you were going 40 when this all happened. If nothing else it will be good to know that these 3 areas are not the problem.
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Old 11-04-2011, 01:14 PM
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vision vision is offline
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I still say rudder. If there was enough force to break the clevis bolt, I think it could have bent the brass. My guess, like mcantamessa indicated, is that you reach a harmonic frequency at the higher speeds that causes the damaged rudder to vibrate. Probably just a slight distortion.

I do not think it the prop (since it occurs with 2 new props) and if it was the prop design, I would think many others would have experienced this issue. But certainly prop, shaft and strut are possibilities.

I am not sure of an easy way to determine if the rudder is the culprit besides changing it out. I wonder if your dealer would have a spare good rudder you could test?
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