DUKE OF DEVONSHIRE

[Harold H. Duncan]

Hi R.G.Y.,
If you can also isolate the engine/boiler base plate from the hull, this will stop transmitted noise through the structure. Rubber mounts similar to those provided for servo mounting will work fine. Just do not over tighten. That takes care of the conducted component of your noise.
Then your radiated sound can be dampened by internal hull insulation.
Simply doing one or the other will only partially dampen the noise, both should effectively eliminate most.
regards
kiwi

[R.G.Y.]

Kiwi,Absolutely right, but the problem is any flexing and the gears I am using will disengage.    This is because the paddle shaft is fixed to the hull sides, the restricted space prevents me installing a separate frame. However I do have another set of gears.( see the arrow ). these will tolerate more movement, I was going to use them in Totnes Castle, but we will see. 
I payed a visit to my model engineering club last night. The way things are going with the boiler new regulations looks terminal for boats. the secretary is posting me a copy. I will know more when I have read them myself. There was one bit of good news the inspector said it is OK to use Rothenberger-Rolot S2 rods, less than a quarter of the price of silver solder, and no flux.    I may be going all electric. Geoff

[Harold H. Duncan]

R.G.C.
to isolate for vibration, you don't need soft very flexible rubber of polyurethane elastimers.
quite hard elastimers work just as well. Even ones  that you have difficulty compressing between your fingers, or denting with your nail.
the original type used in the bushes of car shock absorber/engine mounts or even better the red polyurethane used as after market bushes for the same thing. These will have negligible deflection
They only need to be a mm or two thick to work. Just make sure the mounting bolts to the hull don't touch the engine or base plate. A thin blanket of sound insulation inside the hull, especially under the base plate and your done. Don't forget underside of deck either, but you knew that. 
cheers
kiwi

[Talisman]

Hi Geoff,
Now i'm not going to confess to knowing the answer to the noise problem, however i'm now a fan of Funky Foam ... I love the name, bought a piece and then chopped it up on the laser cutter ... bit like a witch hunt .. if it chops up nice its good if it doesn't it goes in the bin and wasn't good and never sees the light of day again...
Anyway.. I had a problem with sound in my Volcano set up, cut a 'gasket' between motor and mount - sound reduced
funky foam gasket between mount & hull ... sound reduced further .. great

The frustrating bit is the unit made no sound when run outside the hull...
But in my simple mind i managed to see the similarity between a hull and a speaker enclosure ... simple engineering from a simple mind lol ...

My vote would still go with chain / belt over gears ... more forgiving to the simple engineer (me)
All the best,
Kim
 

[Harold H. Duncan]

hope this helps explain better
kiwi

[derekwarner_decoy]

Guys........there is a third possibility here in the actual cause of the resonance 

1. Could the original engine plate not be sufficiently bonded to the hull?

2. If this bond is minimal, vibration/resonance could be amplified by the hull plates/structure 

3. Adding resillance between the offending element & the hull is literally just masking the root cause

Derek

[Harold H. Duncan]

Hi Derek,
The source of the vibration being better bonded to the hull, will result in a better sound transmission to the sounding box, ie the hull. Even though doing this will eliminate extra vibration caused by a loose connection.
To make it quieter we need to isolate the source from the box, in both transmitted and radiated sound.
Transmission path needs to be broken, but equally important radiated needs to be dampened as well.
And heat insulation doesn't always work on Sound.
cheers
kiwi

[derekwarner_decoy]

Hi PD's...... ...kiwi & RGY......this is an interesting subject & I do not want to bog up the thread but it may help

As I see this...we have 3 potential choices

1. eliminate the cause of the noise = eliminate the gears & revert to a silent belt drive
2. isolate the noise = accept that is there & attempt to disguise it by resilisience... it has been accepted that the gearing is not an issue out of the hull
3. harness the noise = accept that it is there & remove the resonance ...absorb the noise through rigidity ......it has been accepted that the gearing is not an issue out of the hull

Derek

[R.G.Y.]

Thank you all for your input most helpful. Derek how could you possible BOG up this thread ( no tomato sause here)  Geoff

[Harold H. Duncan]

R.G.Y. and Derek,
Am doing some research after looking back to see your layout, will get back tomorrow evening, kiwi time.
Have to check something at work
cheers
HarryD

 

[derekwarner_decoy]

Hi Pd's.......  ...RGY.....if you need some extra...just call...we have plenty over here  .......Derek

[R.G.Y.]

 Kiwi .To save you time here are two photos which show the setup.
I have always known Derek had plenty of sause  . Geoff

[Harold H. Duncan]

Hi Guys.
R.G.Y., thanks for posting the photos, gives me a much better idea of the problem, and hopefully some solutions to same.
Now, some assumptions.
The engine runs relatively silently when out of the boat, on the bench.
You have run the engine without the deck secured or screwed down, and its noisy.
Even on the water with deck on and secured its still very noisy.
One disadvantage I have is not being able to hear the noise, which would give a good idea of what's producing it.
Ok, on thing for a start is the gears you gave are straight cut steel ones, and as such are inherently noisy in themselves.
A solution to this is to change to the coarser pitch (larger teeth) gear set. but replace one of these gears with a gear of different material. I would recommend a glass reinforced nylon (or Delrin) pinion, to match the larger driven gear.
This will make the noise generated by the gear train diminish to acceptable levels.
The gear noise is being transmitted in my opinion by the paddle shaft through the two bearings to the sides, which are unsupported along the top edge, and acting as a sound board, similar to the sounding box on guitars, etc. The whole engine / boiler compartment (in common with most model boats ) is the sound box.
The minor path for sound from the gear train is via the engine mounting plate, securely screwed to the bottom. The bottom should be somewhat dampened by the water surface on the bottom of the hull, and think its the sides which are the main transmitting surface to air.
If you can fix the gear-train first, then let us know if the boat is still too noisy and go further from there.
Hope this is of some help
cheers
kiwi

[R.G.Y.]

Harry D. Yes I think the coarser gears are the way to go. beside being quieter they will allow some movement, so a soft fixing can be fitted. Having said that it will be on the back burner for a bit.  Geoff

[R.G.Y.]

Earlier in this thread there was some discussion  on the anchoring procedure and the equipment. I decided on a simple steam capstan on the foredeck, as could be seen in photos of the aft deck. Looking through a book in my own  library I found the photo below.  It is of the Consul ex Duke of Devonshire in 1938 the year of her name change, not too many alterations then. The top of the capstan can be seen, also a samson post which I have  missed out. The samson post makes me think the anchor was on a rope (hawser) not a chain Especially looking at the amount of rope  about the deck. Geoff