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[ukmike]

The hull acts as a giant resonator box which B&O would be proud of.
It is particularly noisy when the two motors run, even when tapped or some small items are dropped inside it.
For info it is double plank in frame amounting to 5.5mm thick, 1.3 mtrs long and 380mm beam.
It's driving me crackers and not even finished yet !!
Mike.

[Tug Fanatic]

Is the noise coming from the motors, the drive system or both?


Are you using the sort of motor/propshaft couplings that would let you mount the motors flexibly?

[Hotglove]

Self-adhesive soundproofing pads from any car audio shop?

[JimG]

Builders spray foam? Also adds some bouyancy if the hull floods.
Jim

[Andyn]

Noise is caused by vibration in models, so find the source of your vibration and you've found the source of your noise. If you're using those red or black plastic universal joints - bin them, they're garbage. Keep the brass parts and replace the coupling with some 6 or 7mm ID silicon car hose, available on ebay for £3 a meter.


As a further point, never use builders foam in a boat. Builders foam never stops expanding and contracting, and I've seen it more than once (including learning the hard way) where someone has used it for buoyancy and it's expanded on a hot day and popped the deck off.

[big_bri]

Noise is caused by vibration in models, so find the source of your vibration and you've found the source of your noise. If you're using those red or black plastic universal joints - bin them, they're garbage. Keep the brass parts and replace the coupling with some 6 or 7mm ID silicon car hose, available on ebay for £3 a meter.


As a further point, never use builders foam in a boat. Builders foam never stops expanding and contracting, and I've seen it more than once (including learning the hard way) where someone has used it for buoyancy and it's expanded on a hot day and popped the deck off.

Totally agree, I've used silicone tube for years, regarding the foam, it also retains water should it enter the boat and can cause no end of problems.

[Liverbudgie2]

Bathroom sealant also works very well, have used it for years with no problems.

LB

[CGAux26]

Make sure shafts are STRAIGHT (roll them on a flat surface and listen for bumping noises).  Get your shaft alignment as near perfect as possible, angle and offset.  Remove the sources of the noise and vibration and insulating may not be necessary.

[ChrisF]

Mike - having read your build blog previously I doubt that as others are suggesting that you have any issues with the alignment of your installation!

One thought might be that noise might be being transmitted from the mountings you have in the frames to the hull?

Once in the water the noise will probably be far less anyway due to the damping effect of the water. In air it's just acting like a musical instrument, though not as tuneful!

Chris

[johnv]

Hi it's John V try a bit of foam or rubber under motor but like the other chap you will find it will better once in the water cheers John V

[ukmike]

Thanks for the replies so far..


A little more info may help, firstly the motors are outrunner1500 watts each so the couplings are industrial helical types, ballraced,  the shafts and tubes are absolutely true, anyway, the amplified sounds are nothing to do with the transmission system, it's the cavenous wooden hull that is the root cause.
No silicone will will ever be used in my models due to the contamination to any paint or varnish.
Rubber mounting the motors is not feasable in this case, o.k. maybe for smaller motors.


May well try some high density vibration absorbing foam which is often used in cars, the drawbacks are weight and price.


Mike.

[tigertiger]

If it is purely the effects of a cavernous hull, try placing old egg boxes of foam rubber chunks into the hull as this will deaden sound.
If this works you can think about buying flame retardant (just in case) foam or acoustic tiles (wall type) as a more permanent solution.
Just a thought.

[Hotglove]

An alternative to builders foam, if weight is not too much of an issue, could be closed cell buoyancy foam as used in life jackets, etc.
An alternative would be to experiment with vibration dampers (used in the car industry and to deal with vibration on overhead power lines)

[Pat Matthews]

And as my mechanical vibrations professor often reminded us: We DAMP vibrations, but we DAMPEN a towel to wipe egg off of our faces.
Of course, any model boater worth his salt dampens his boats frequently!

[tigertiger]

I also remember something like, we don't damp vibrations by making things more rigid.

[steamboat66]

there is a vibration that you CANNOT stop. it is the torsional vibration caused by each pole in turn as they energize and de-energize. soft mounting of the motors, and soft couplings will reduce this. but as others have said, the noise is worse out of the water.

[ukmike]

there is a vibration that you CANNOT stop. it is the torsional vibration caused by each pole in turn as they energize and de-energize. soft mounting of the motors, and soft couplings will reduce this. but as others have said, the noise is worse out of the water.

Set stated earlier, it's nothing to do with the motors and I take your point that it should be somewhat quieter
when, (if), it ever sees water.
Have some 10 mm high density sticky backed foam arriving shortly so will see what that does.


Mike.

[ukmike]

Have gone with the sticky high density foam, would have been easier to fit earlier in the build as it wants to stick to anything it touches.Although not quite finished completely, it seems to have had a significant dampening effect on the overall sound and general noise levels.
A few pictures show the progress.
Mike.

[ballastanksian]

When I first test ran my Destroyer on the bench, it sounded like a moped. I checked the shafts, one of which was quite warped and rectified that. Then still sounding a little noisy (to my ears) I shrugged my shoulders and took it to club where on first sailing, it was much quieter.


I agree that at first it is worrying and makes you wonder if it is worth carrying on with as surely the noise is going to be embarrassing at the lake, but it will get better and sound less noisy in the water especially once you have put the superstructure on and gubbins in.


There are lots of good ideas and sensible procedures to act on which are well worth trying.

[CGAux26]

What are those shaft couplings and how do they take up misalignment?

[ukmike]

What are those shaft couplings and how do they take up misalignment?

Firstly they are not designed to take up misalignment although they can tolerate  small amounts.

They are solid aluminium which are spirally cut to the centre bore. This allows absolutely no slop, noise or wear. The spiral is able to flex in any direction all at the same time up to several thousand revs..
They do rely on as near as possible perfect shaft to motor alignment in the first instance and therefore not able tolerate or cope with sloppy installation.


Hope that helps.


Mike.

[CGAux26]

Thanks.  Where did you get those couplings?


And as for not tolerating a lot of misalignment, my machinery engineering background says you align shafts to within a nat's whisker, regardless if the coupling manufacture claims big tolerances.  Misalignment causes wear on bearings and couplings, and vibration and noise.

[ukmike]

Thanks.  Where did you get those couplings?


And as for not tolerating a lot of misalignment, my machinery engineering background says you align shafts to within a nat's whisker, regardless if the coupling manufacture claims big tolerances.  Misalignment causes wear on bearings and couplings, and vibration and noise.

They inevitably came from China.

[Colin Bishop]

As already mentioned, adding dampening is simply addressing the symptoms rather than the cause of the problem which is driveline vibration. The cause is maybe the coupling but it could also be the shaft being out of true and vibrating within the tube. It can be quite difficult to identify and even more difficult to fix. Been there, done that! No simple solution, you just have to work through the possibilities.

Colin

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[chas]

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