need help with new flounder rig - Pensacola Fishing Forum

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Old 05-21-2012, 08:51 PM   #1
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Ruby Red Lip
 
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Default need help with new flounder rig

Just got my air motor together and I'm having a problem with bad vibrations on acceleration ....

The unit consist of a Honda clone (predator) 13 HP with a 36" 3 blade composite prop. It is mounted to my existing poling platform that is built out of 1"5/8 pipe rigid as can be but tall. The engine is mounted to a 1/2" plate of aluminum that is mounted to a wheel bearing hub attached to poling platform.

I am having severe vibrations at mid throttle. The engine will run smooth at idle and at wide open throttle (3,300 rpms) I thought it needed more bracing so added it and still the same. Also exchanged engine and still the same. Engine was hard mounted so I thought that was it so I added neopreme bushings and still the same. Pulled prop checked balance and checked good. Ran engine without prop and no vibration put prop back on and vibration returned. Tested prop in everyway I was told by Manufactor and all I could find was an 1/8" difference on one blade if that.

I'm just wondering if its just normal or am I missing something. Any and all recommendations would be greatly appreciated. Thanks in advance.

Capt. Travis
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Old 05-21-2012, 09:03 PM   #2
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Old 05-21-2012, 09:04 PM   #3
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Old 05-21-2012, 09:07 PM   #4
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Old 05-21-2012, 09:12 PM   #5
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Do you have a way to spin the prop with out the engine? An 1/8" in a 36" blade is alot at 3K RPM.A boat prop shop might could help.If thats not it,it might be the engine,offset cut crank shaft.A dial indicator would verify this.
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Old 05-21-2012, 09:23 PM   #6
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Thanks for your reply.... I've checked the prop and it was barely out within manufactures specs lol as they say. What has me puzzled is that if it was the prop wouldn't it get worse as the rpm's increased. As is it gets smoother at wide open throttle no vibration at all from the norm as well as being smooth at idle. I originally thought the counter balance was off so I exchanged engine and ran it on the bench and it had no vib at any range. We measured the tip of the prop at the same position and found one blade off but within specs as per manufacture ... Just didn't know if I was over reacting or is this normal.
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Old 05-22-2012, 04:26 PM   #7
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Another thing to think about,thats a single cylinder engine,think of ya lawn mower and how it vibrates.And theres a whole bunch at play when that prop gets added to an engine,its more complicated than what I know.If its to bad,you might try a pulley system where the prop is separate from the engine.

Just how bad is the vibration? Think lawn mower,one with new blade,VS one with bent/wore out blade?

Yes and no one the vibration getting worse or better as the RPM's increase,harmonics/dynamic come into play there.Kinda like a tire out of balance on your truck,if its just a little out you notice that at certain speeds its smooth,but slower/faster it beats ya to death,same concept with the prop.

If you have a way of measuring the prop while on the engine you might find it there,turn the engine by hand,and measure each blade's run out.And I dont think an 1/8" is acceptable.

Last edited by drifterfisher; 05-22-2012 at 04:32 PM.
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Old 05-22-2012, 05:04 PM   #8
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I may have missed something but did you weigh the blades? Are they fixed pitch?
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Old 05-22-2012, 07:03 PM   #9
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Thanks again and I agree that an 1/8 inch at 3400 rpms is way to much as did manufacture they agreed to send a new one. I also talked with a fabricator in Texas that has built several and I explained the symptoms and the first thing he asked as he laughed was it sitting on the trailer and it hit me lol it was and had little to know vibration in the water... Thanks million for your reply. I'm sure what vibrations are there will be cured by the new prop.
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Old 05-22-2012, 07:05 PM   #10
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Blades are adjustable with blocks. Weight was right on.
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