Rudder Vibration, Could Need Some Help

[Loredo]

Hi All,
I need some help with this problem:

The boat is a 2006 Sun Odyssey 49.
Anything above 7.5 K there's a vibration ( sounds like a rumble ) coming form the rudder area. It doesn't matter if under engine power or sails only. The higher the speed then louder it becomes. It is not really loud but still enough to be noticed. At first I thought it's the prop or prop-shaft bearings. I replaced the bearings to no avail. The prop is a Maxprop which I'm going to replace anyway but that's a different story....
I don't think that the "rumble" I hear is related to the prop because it doesn't matter if the shaft is locked or spinning free under sail. All I know for sure is that this rumble is strongest around the rudder area. If it really is a rudder vibration, it can't be felt in the steering. Hard to say but I can't feel any vibration in the hull either.

I've never had a spade type rudder before so maybe it's just normal? I don't think so but what do I know...

Also, all my previous boats had a stick. Thus, I'm not very familiar with steering wheels and the related components. In other words, I have no clue where to start to look at. I guess there's more to it than tighten a couple bolts & nuts, right?
Don't get me wrong, I can and do fix everything on the boat on my own. I'm just not used to have to deal with a "complicated" steering system.

Any and all input is more than welcome!

[delmarrey]

Welcome aboard Lorado!

Have you checked the lower rudder bearing for looseness? IAW- wiggle side to side.

[Loredo]

Yikes!
Now that was a super fast reply, thanks!
Yes I did check for any play in the rudder during the last haul out, it was rock solid. At least that's my impression. One thing I noticed tho was that I was able to lift the rudder a tiny bit. Also that's difficult to quantify since the rudder is HEAVY. Side to side play, none. Up a "little" maybe a couple millimeters.

Maybe I should have said this in my first MSG? The boat is in the water right now and I can really check out things only next spring when it'll be time for the annual haul out / bottom paint. For now I'm looking for anything that I could check under deck.

I don't know if this could be of any importance. The boat has two steering wheels, right? The one on the left feels a little "mushy"/less precise than the one on the right side.
30+ years with sticks and now all od a sudden TWO steering wheels, lord help me! LOL

Thanks!

[delmarrey]

Another thought. If yours has steering is cables you could be getting some harmonics through the rudder causing the cables to vibrate.

I have hyd steering but when I'm surfing a wave at 9 kt+ I get a nice little humming thru the hull back at the rudder. Others here have also commented on rudder harmonics.

I think I'd go below during the time and see if I could find out where it's originating.

[Sailmonkey]

How much hull to rudder clearance do you have? If too great the turbulence there could be a rumble.

[fstbttms]

Would be interested in hearing the "different story" regarding the Max Prop.

[Loredo]

delmarrey,
harmonics through the steering cables? Could be but... The "rumble" that I'm getting sounds more like a worn out cutlass bearing. I don't think ( add any and all disclaimers here about me *thinking* ) that the cables would make a more "high pitched" sound than that low frequency noise ( rumble ) that I'm getting. In fact, first thing, I replaced the cutlass bearing this spring since it had some minor play in it but that wasn't it. Also the Maxprop has more play in the blades than what I like thus I'm going to replace it. Yet, the prop can't be it since, well I already mentioned that my buddy Rumble is there with the prop stoped. What makes all this even worse, I don't know if I should worry or not. Maybe it's just the nature of the beast???
Then there this thread "Rudder Nightmare at Sea" that makes me think : http://www.cruisersforum.com/forums/...ea-114018.html
OK, that's a Beneateau 50 which is to my best knowledge the same hull yada yada yada as my SO49. I would hate to say bye bye to my rudder...
You know, sh** always happens when you need it least.

Sailmonkey,
good point! Thanks! I've looked up a picture I took when I had the boat hauled out this spring. Hard to say from the picture but I'm guessing that there's less than an inch between the rudder and the hull. That shouldn't be it either.

Keep 'em coming!

Thanks,

Loredo

[Loredo]

fstbttms,
On my previous boat I had the Maxprop rebuild twice in ten years. ( BIG bugs for a rebuild if you ask me...) I always serviced it every year. One fine day went for a day cruise. Headed back to the harbour I start the engine, put it in gear, no go. YIKES! Long story short, the Maxprop got lost! Before you ask, the pin WAS in the bolt. I had it installed on my own and am 100% positive that it was done right. On that boat I went back to the original fixed two blade. Guess what? The fuel consumption dropped instantly a solid 30%! Now, the Maxprop needs constant rebuilds, is rather noisy, says babye every now and then to it's legit owner ( two friends of mine lost 'em also ) and is the worst prop when it comes to "mileage".

Not again!

I'm replacing the Max with an Autoprop. Yes, I've read and heard of all the horror stories about the Autoprop but it can't be worse than the Max.
I ordered a H6-534 last week. Install it next spring. We'll see!
Should be interesting to see what I find out about the Auto compared to the Max.

Makes sense?
To me it does!

[fstbttms]

I have been installing Max Props for years (and servicing them for almost two decades) and have never heard of one being lost. So many nearly simultaneous failures would have to occur for a properly installed Max Prop to actually come off the shaft that it is very hard to imagine that happening. And I assure you that frequent rebuilding is not an quality typically attributed to Max Prop. But it's your dime. I won't even begin to give you my opinion of Autoprop.

[Loredo]

fstbttms,
well, take my word, the Max got lost and did not even say bye bye.
When I got towed into the marina everybody was saying, Nahhhh that's your fault! You did not set the pin into the nut. Never heard about one getting lost... Well, I was rather well trained working on the Max. Between trying to find the right setting ( 2-3 tries ) and rebuilds, I was used to it. To add to this, I still can remember visually that I did install the pin. ( Besides the fact that I went to get a new pin and then installed it.) I'm 100% positive that I did it right! What happend then? I do not know! I'm with you that looking at the Max's design it's hard to explain how one can get lost! But I did... In the next couple years two more Max'es got lost by friends of mine too.

I understand that the Auto is a very controversial prop, at least on the paper it promises me a better ( motor ) cruising range which in the Adriatic sea is very important to me. In the summer, more often than not the wind is very, very light. Not good when you plan a single 200 mile stretch ...

Will the Autoprop do good for me? Only time will tell.

[Jim Cate]

Loredo, your experience re improving fuel economy is a factor often overlooked by folks who champion the use of feathering props (not just Max props... all of them). The thing is, all feathering props have blades with no twist built into their shapes. This has an adverse effect upon their efficiency, ie their ability to translate engine power into thrust, and it simply takes more fuel to drive the boat at any given speed.

You are committed to the Auto prop for now, and I hope that you have a good experience with it. Some folks do,others have less luck and a long history of difficulties, as fstbtms suggests. If that proves true for you, consider one of the better three blade folding props. The Flex-o-fold props have done well in tests, and we have now had 10 years of excellent service from one. Previously we have used two and three blade fixed, Martec folding, Autostream feathering and Gori folding props. The Flex-o-fold has been the best of the lot for our usage.

Now, as to your rumble: does the frequency of the rumble change with speed? One source of noise that has not been mentioned is simply from turbulence around the stern... quarter wave generation, cavitation around the rudder or strut and prop and so on. With lightly built hulls such as yours, this turbulence can easily be heard inside the boat, and would seem to emanate from the aft portion of the hull. This noise would not appear to change frequency with speed change, but might well get louder as speed increased.

Good luck in tracking down the source... such things can be aggravating even if inconsequential!

Cheers,

Jim

[Cheechako]

A Max Prop problem is rare for sure. I've had five of them, some were used when I got them. Never an issue with any.
Your boat has two wheels... is it a model with two rudders also? If so maybe they arent sync'd? It does sound alot like a prop thing, but if you are locked in gear I guess it really cant be that. Maybe a rudder that isnt perfectly symmetrical and/or some play in the cables?

[Loredo]

Jim,
thanks for chiming in helping me to troubleshoot my rumble!

I think well all know that a simple fixed blade prop is less prone to problems over time. Yet, I LOVE the almost extra knot a feathering prop gives me in light winds under sail.
You hit the nail on it's head when you say that I'm "committed to the Auto prop" for NOW! Perfection does not exist so I'm rather sure that the Auto will have it's downsides too but having had "mixed" results with the Max... it's time to move on and try something new. Much like, you don't buy the same boat twice, right?

Your point about turbolence and cavitation sounds like a possible cause to me. I'd have to lie but off of my memory it seems to me that the frequency does not change but the rumble becomes louder when speed increases. @ 8 Kn I can hear it my wife won't. @ 9 Kn it IS very noticable but wifey still can't pick it out. @ 10 Kn it's LOUD but I've been there only a couple times for short bursts.

Hmmmmmm, OOOK then here's yet another question.

How can I make sure then it's not the rudder and I'm not looking for trouble???

Cheechako,
nope, the boat has a single rudder. I agree, it sounds a lot like a prop problem but I also think that one is ruled out.
Rudder that isnt perfectly symmetrical. Good one I hadn't thought about! I will check this once the boat is on the land
Some play in the cables? Interesting! Could play in the cables make the rudder resonate/vibrate that bad? That one I can check next time on the boat!

THANKS!

[donradcliffe]

My max prop would vibrate when motor sailing above a certain rpm and boat speed. The vibration would be triggered by surfing down a wave at over hull speed, but would remain until I throttled back. Refurbishing the prop helped, but it didn't make it go away. Never did figure out what the problem was, but since I only sailed that way very occasionally (like to beat a weather front), I ignored it.

Rudders can vibrate at high speeds, but its only an issue in performance boats. The usual cause is that the trailing edge is too wide and sheds vortices. On a race boat its usually a good sound, because it means you're going really fast.

I had a similar problem on a performance cruiser I delivered transatlantic. When the boat got up over 12 knots, the rudder started to shake. The immediate solution was to have the crew reef down the twin headsail rig in the squalls to limit the boat speed to under 10k. When we arrived in St Lucia I went over the side and shook the rudder to see if there was a bearing/rudder issue. It felt and looked fine, but the rudder's trailing edge was half an inch wide. If it was my boat, I'd re-fair the trailing edge to 1/8" or less.

[Cheechako]

I was just thinking with some play in the cables the rudder might be able to "wobble" very slightly from side to side.... It would be interesting if you could talk with owners of other identical boats.... maybe it's a design issue ... some interaction between the prop turbulance and the rudder...