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[guitar man]

Hi all
     
     Have spent the afternoon trying to quite down my perkassa, have re- done the motor mount which resulted in no real improvement.
Ripped out the propshaft, and have lightly expoxied it back in place which help greatly. have also found that if I balance the battery on a couple of batterns  just above the prop shaft this kills some vibration again helping. Have also found that the motor disconnected from the prop shaft is fairly quite. So now to the question, the prop shaft is quite long, would there be any benefit in machining a third bush to sit half way down the inside of the prop shaft tube or am I barking up the wrong tree.

As always many thanks in advance for any thoughts

                                              Regards Tony

[Welsh Wizard]

certantly would help mine has a similar noise think it is the same problem try it and let us know how you get on


Dave

[DickyD]

Hi Dave I agree its probably the prop shaft.

Nice to see you back.

[MikeA]

i allways have noise problems, check the propshaft isnt bent also check the coupling. I once tried a peice of silicone tube between the motor spindle and the propshaft, the silence was bliss. I thought it would be sufficient but i used it on a brushless powerboat and it snapped. would probably work on a slower prop speed, the rubber coupling i got from MMB works great though on my slower boats

[John Mk2]

On my scale boat's I used silicone adhesive instead of epoxy for mount to hull  Work's very well as it adsorb's a lot of vibration's (Hull resonance)   

[irishcarguy]

It may help if you put a rubber pad between the motor mount & the boat mount but make sure the rubber is not too soft & use lock nuts on the mount bolts. Mick B.

[DickyD]

Could be the coupling, some of the cheaper ones are not really balanced well.

[Circlip]

No simple answer, the hull is like a loudspeaker cabinet and we used to go to great lengths to deaden the box. If you look back at what was required on I/C mountings for the engines, Rubber-flex mountings to isolate the motor from the hull. Then deadening the "Box" the motor is mounted in, all the flat internal surfaces reflect the sound and act like a drum skin. Already mentioned is the shaft straight ? Fitting a bearing halfway down may be a problem ensuring all the holes are perfectly inline. Is the motorshaft and propshaft perfectly inline with each other? U/J's make for a lazy way of coupling as many people only get the line up somewhere near and due to the construction of Huco's and the like, the coupling is made from rigid materials with no deadening materials in them. ( Lot to be said for the leather disc type and rubber shock mounts).

  Good luck, it may be a frustrating trail.

  Regards  Ian

  Also, is the tube straight and the bushings inline?

[pompebled]

Hi Tony,

Adding a third bushing will help, but don't position it exactly half way, as the resonances may only move up one octave instead of going away...

Is the stuffing tube filled with light grease?
This should dampen a resonating shaft rather well.
Downside is the added drag from the grease, robbing you of speed and runtime.

Regards, Jan.

[Shipmate60]

Have you got a support on the propshaft right on its inner end.
This will help reduce the vibration which is causing the noise,
If the shaft has a, "A" or"P" frame on its outer end, it is obviously supported through the hull so another support on the inner end will help reduce vibration.
Also does the inner shaft have much exposed from the outer shaft, this again can cause vibration so keep as short as realistically possible.

Bob

[guitar man]

Thankyou all for your responses. Plenty to go at there, I will start with a third bush since the tube is now out of the boat and will work through the ideas. Though I have a feeling it might be a case of compromise. I will let you know how it goes.


                       Regards Tony

[gwa84]

another option is sound proofing mat as used by pc gamers with tons of fans in the old days stops flat serfices resonating

[guitar man]

Oh what joy finally a relatively quite boat

Remade the prop shaft as it did seem a little bent and changed it to 5mm  no improvement
changed the coupling for a fixed one no improvement
Gave up had Christmas, then went back with a vengeance ripped it all out again fitted the prop tube and measured its angle remade the motor mount to suit the measured angle no improvement
Found out that when I tighten the nut up on the uj, noise got terrible this then lead me to look at the thread. When tighten up it was throwing the shaft well out of true.Remade shaft again but this time screw cut it on a lathe. At last some improvement
Inserted some grease in the prop tube some improvement again
Made some new end bushes for the tube as they seemed a little loose and fitted a solid type of rubber couping (home made) can now hear the radio when the boat is running.
Well you did ask me to let you know how I got on 

Thanks again for your help

                                       Regards Tony