Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[RAAArtyGunner]

What about, 'covering/encasing' the bearings with sound deadening material.??


You did say they are metal, so metal on metal equates to sound output.

[derekwarner]

Mike...you can get a lump section of steel into the hull...& mount a dial indicator [rotating the coupling by hand] and validate the end diameter and also the actual shaft just outboard of the coupling's

These couplings have a 0.02 TIR specification, [although this is still a metal to metal dimensional tolerance] however ideally you require zero TIR or and a resilient element in the coupling to eliminate the metal to metal contact

My best assumption is that the couplings are creating a harmonic resonance which at speed is the root cause of the sound amplification you are experiencing

Derek

[ukmike]

I don't think anyone has asked you, are the props balanced?. It not unusual for them to be miles out, even the good ones. Taking the props off and running it is an easy check.
Chas

Not fitted the props yet and yes they are balanced, as a matther of interest, they were balanced to 15,000 rpm so all should be well with them.

[ukmike]

Mike...you can get a lump section of steel into the hull...& mount a dial indicator [rotating the coupling by hand] and validate the end diameter and also the actual shaft just outboard of the coupling's

These couplings have a 0.02 TIR specification, [although this is still a metal to metal dimensional tolerance] however ideally you require zero TIR or and a resilient element in the coupling to eliminate the metal to metal contact

My best assumption is that the couplings are creating a harmonic resonance which at speed is the root cause of the sound amplification you are experiencing

Derek
[/quoteGood point Derek but I don't have the wherewithall to do all that, but, I do have a pair of these...The socket screws can be aligned to be opposed to each other and the composite "plum" isolates the two halves so they don't touch.Haven't tried them yet but will do that.
For those who keep mentioning  rubber mounting the motors.
That was the very first thing that I tried, I isolated the everything associated wth the motor mounting including lining the mounting holes for the bolts so that by the time I had finished absolutely everything to do with the motor mounting was isolated from the wooden hull, no joy, no improvment.
I'll give the plum couplings a go and that will be the end of it.
Derek, here is a photo of the plum couplings, your thoughts appriciated.
Mike.

[Hotglove]

A further refinement could be some wedges of foam, as used in an anechoic chamber, they are startlingly effective, as anyone who has been in such a chamber will tell you. A weird sensation to speak in a loud voice and hear next to nothing.

[Colin Bishop]

Some good ideas here but, as Mike appreciates, it is always best to concentrate on the problem rather than the symptoms. If an electric motor setup is in perfect alignment and the prop is balanced there should be nothing more than a gentle hum.
My fishery cruiser suffered from a similar problem. One shaft ran sweet as a nut at all speeds, the other made a terrible noise. I tracked the main problem down to a slightly bent tube but the original prop was also slightly unbalanced as I don't think the socket was quite straight in the boss. I had to change the tube (difficult) and props but the problem has almost gone away now although the other shaft still runs better.
Colin

[Hotglove]

Just a point that might help someone in the future, I recently had to make new propshaft (3/16”) and the stainless rod was delivered slightly bent. Local archery shop used a precision arrow straightening jig and, when he had finished there was no perceptible imperfection, (did it for free too) same would work for tube, arrows are tubular.

[nemesis]

The coupling has a steel bolt off centre, that could cause an imbalance, yes I know we are nitpicking, I also note that the mountings are wood, bonded to the hull therefore transferring any vibration off the motors to the hull. My thoughts only, hope it helps,nemesis

[CGAux26]

I always use an L-shaped aluminum motor mount, and put a 1/16" rubber pad under it.  I left it out once and the difference in the on-bench noise was noticeable.