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Quesiton about Turning Fins and vibration


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OK. I have had my boat for about 4 months now and I really like it.

However, there are a couple questions I had and what better site to get the answers?

1st - Turning fins...What direction are they supposed to be? Slanted side forward or straight side forward? And does it make a difference. Mine have the flat/straight side forward which is opposite of every other Malibu I have seen and payed attention to. Also is it possible to turn the fins around either way?

2nd - My boat has a pretty strong vibration(almost a cavitation feeling) that can be felt during hard starts with a footer or slalom skier in tow. It is right at about 18-25 mph when the vibration starts and stops. It only happens then and before and after it is smooth as butter.The previous owner informed me about it and said he had the prop and shaft checked and all was fine. I am wondering what is causing this vibration. Could it be the above turning fins? Could it be something with the motor itself? It is not a normal vibration in my opinion.

Any advice and or opinions, as usual, are welcome.

thanks

man I spelled "question" wrong...what a moron! :lol:

Edited by areamike
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Which Prop do you have? I had a pretty good vibration like you described pulling up slalom skiers with the standard 3 blade stainless prop on my '01. Replaced it with an ACME CNC prop and it went away (mostly)

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OK. I have had my boat for about 4 months now and I really like it.

However, there are a couple questions I had and what better site to get the answers?

1st - Turning fins...What direction are they supposed to be? Slanted side forward or straight side forward? And does it make a difference. Mine have the flat/straight side forward which is opposite of every other Malibu I have seen and payed attention to. Also is it possible to turn the fins around either way?

2nd - My boat has a pretty strong vibration(almost a cavitation feeling) that can be felt during hard starts with a footer or slalom skier in tow. It is right at about 18-25 mph when the vibration starts and stops. It only happens then and before and after it is smooth as butter.The previous owner informed me about it and said he had the prop and shaft checked and all was fine. I am wondering what is causing this vibration. Could it be the above turning fins? Could it be something with the motor itself? It is not a normal vibration in my opinion.

Any advice and or opinions, as usual, are welcome.

thanks

Reading the first sentence, I would suspect that your prop is cavitating. But that should occur only when the propeller is under a lot of torque, during your hole shot. If a strong vibration is present at speed, something else is happening. Even though the previous owner has told you he has had it checked, I would certainly (1) look at the prop for damage, bent blades (2) check the shaft for aligment to the engine - this is not that difficult but you may want to have a boat dealer do this (3) the shaft itself. I would recommend crawling under the boat and looking for dings, damage to the under side running gear, fiberglass, prop, and rudder. On the fins, try and see if you can move them - grab them and see if they wobble - they could be loose!!!

Finally, post some pictures of the fins - I cannot visualize what you are describing.

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Thanks guys,

Dan. It is the Standard Stainless 3 blade that was shipped with the boat.

My cousins have a four blade stainless with slightly different pitch I plan to try this weekend.

Gordo. The vibration only happens during the hole shot. It is not "noticeable" during speed. However, I have noticed that my rear view mirror is vibrating slightly at speed and makes the skier looks distorted...makes your eyes feel funny... Crazy.gif

Also, I forgot to mention. The boat vibrates more when turning left than when turning right.... Dontknow.gif

I've looked closely at everything under the boat. It is ALL stainless and all looks fine. I even ran my hands over all edges etc and everything seems perfect.

I'll post a pic of the turning fins in a few minutes.

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Mine are straight toward the stem and angled aft, just like yours. Well, mine aren't stainless.

Crazy.gif I'm soooo confused. Is there a norm to these fins? I need to lay down...my head hurts!

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I just went down to look and my fins are the same as yours.

They are turned clockwise so the leading edge of the fin is slightly to the starboard and the trailing edge is slightly to port.

Straight edge in front slanted edge trailing.

OH...except mine aren't stainless either.

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Mine also are like yours....btw, you should try a good 3-blade CNC prop like an ACME 515

I'd love to if there is a try before you buy option.

I'll try my cousin's 4 blade this weekend. It is stainless as well though. One person mentioned that it could be because of all the Stainless gear. Stainless Prop, Rudder, Shaft etc. None of it "gives" at all which may cause more rigidity amongst each part against the other...

OH and Dan....that is wierd. My Cousin's boat is the EXACT same as yours, but their fins are opposite of mine. 2001 Sunsetter LXi, thus opposite of yours.

Edited by areamike
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Any chance that the vibration is coming from the rack behind the steering wheel and not from the underwater gear? That generation seems to be more sensitive to vibrations in their rack. That said, new props have eliminated these vibrations. In some cases, the rack itself needed to be replaced.

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Any chance that the vibration is coming from the rack behind the steering wheel and not from the underwater gear? That generation seems to be more sensitive to vibrations in their rack. That said, new props have eliminated these vibrations. In some cases, the rack itself needed to be replaced.

hmm...The rack? Is that the whole "unit" under the dash that holds the steering wheel and is tangled with wires?

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Any chance that the vibration is coming from the rack behind the steering wheel and not from the underwater gear? That generation seems to be more sensitive to vibrations in their rack. That said, new props have eliminated these vibrations. In some cases, the rack itself needed to be replaced.

hmm...The rack? Is that the whole "unit" under the dash that holds the steering wheel and is tangled with wires?

It is connected to the steering wheel, not sure about your wires. You're in the right spot. If there is a problem with your rack or rudder, I would think the vibration would be limited to your steering wheel and perhaps mirror. If it is something else, then the Butt Dyno® should register the vibration as well.

I'll be very interested in the results of using your cousin's 4blade. My .02 is on your prop.

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Any chance that the vibration is coming from the rack behind the steering wheel and not from the underwater gear? That generation seems to be more sensitive to vibrations in their rack. That said, new props have eliminated these vibrations. In some cases, the rack itself needed to be replaced.

hmm...The rack? Is that the whole "unit" under the dash that holds the steering wheel and is tangled with wires?

It is connected to the steering wheel, not sure about your wires. You're in the right spot. If there is a problem with your rack or rudder, I would think the vibration would be limited to your steering wheel and perhaps mirror. If it is something else, then the Butt Dyno® should register the vibration as well.

I'll be very interested in the results of using your cousin's 4blade. My .02 is on your prop.

we shall know tomorrow. I just talked to local BU dealer. He says 9 outs 10 times, it's the prop.

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I would agree with your dealer - probably the prop. IMHO, I would buy a Nibral propeller and use your ss one as a back up. You can search the site for (numerous) discussions regarding ss vs Nibral (aka bronze), but I would never, ever run a ss prop. Stainless is more expensive to buy, more expensive to repair, and when you hit something, it is more likely to transmit the damage to your shaft/tranny/v-drive. Look at it this way: something has got to give when you hit a rock, or log. I would rather it be my prop - the cheapest thing to fix.

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