Tips for building an Aluminium boat so as it is quiet?

Discussion in 'Boat Design' started by RSD, Jan 15, 2023.

  1. RSD
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    RSD Junior Member

    Aluminium boats have a reputation for being noisier than similar fibreglass boats - any tips for building a quieter aluminium boat? Either design tips or production tips?
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Define... nosier....?
     
  3. RSD
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    RSD Junior Member

    Louder inside
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    So...that means noise from the ER and possibly also the propulsion side?
    In which case, there are many ways in which you can reduce the noise inside the ER from being transmitted externally.

    Such as:
    Noise Barriers | Pyrotek Soundproofing Solutions https://www.pyroteknc.com/products/noise-barriers/
    and
    Soundproofing Foam and Absorbers, Pyrotek Noise Control https://www.pyroteknc.com/products/sound-absorbers/

    And of course depending upon the size of the engine..you can also encase the engine too.
     
  5. RSD
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    RSD Junior Member

    I'm thinking more vibration of and through the aluminium - that seems the to be the difference between aluminium and fibreglass. Harmonics possibly play a part too.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    So..not noise then.
    Vibration...
    Hmmm..that's a very different proposition to - noise!

    Says who and from where and what issues related to it?

    Look at the the material properties..and you'll realise, what you're saying makes no sense re: vibration!
     
  7. fallguy
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    fallguy Senior Member

    Is this still planned as twin outboard Poleson?

    The main sources of noise would be the waves hitting the hull and then engine sounds. Engine vibrations are more related to synchronization than much else. So what you do is when you start twin engines, in a proper control, you put the engines in gear and then press a button to synchronize so they are running at the same rpms. In my controls, I press a button to allow gear shift and then once in gear, same button again synchs the controls so I can run on one stick.

    When the engines operate at varying rpms; you do get some odd vibrations and the hull type is largely irrelevant.

    The loudest noise in ob is the engines themselves, which can be mitigated by distance above deck, bulwarks, etc.

    Reducing ambient sounds of water on the hulls can be done by creating watertights or using buoyancy foam to make the boat pos buoyant. I am not familiar with the methods used, but generally, putting the foam directly on aluminum may be frowned upon for wet bilges.
     
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  8. bajansailor
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    bajansailor Marine Surveyor

    @RSD could you maybe give us an update as to your latest thoughts re the design of your proposed aluminium dive boat?
    I will second Fallguy's question re if the Poleson cat is still the main contender?

    Re an ally boat being 'noisier' inside, do you mean in the hulls, or in the wheelhouse up on the bow of the boat?
    Will the wheelhouse be enclosed and air conditioned re your fierce Red Sea temps, or will it be open?
     
  9. comfisherman
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    comfisherman Senior Member

    I had one for about a decade, we used leaded foam, paneling, eliminated hatches to the engine room. Had lots of high density foam with lead foam backed panels behind the wood work.

    Then built a glass boat.....
     
  10. Flotation
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    Flotation Senior Member

    Are sound and vibration not very closely related?
     
  11. fallguy
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    fallguy Senior Member

    The sound produced by my outboards is much louder than the annoying vibrations and hum caused by engines not synched. Yes, the vibrations create sound, but it is important to be clear on these issues.

    Inside the cabin, engine noise is virtually nil, but vibration hum is loud..until synch
     
  12. RSD
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    RSD Junior Member

    This is for a different project but also in the Red Sea - aluminium boat building hasn't yet taken off in Egypt but a local shipyard is wanting to get into it now making motor yachts in the 15-20 metre range.

    Still keen on the Poleson, but possibly now with Mercruiser diesel and sterndrives instead of outboards.

    OK cheers - good to know!

    OK very good to know - would not have thought of that being a problem!

    That wasn't the reason for the potential switch to Mercruiser diesels with stern drives - but it might be an added benefit!

    OK will be interesting to see what I can find out about that.
     
  13. RSD
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    RSD Junior Member

    For the dive boat project the Poleson Cat is still the plan, I'm not in Egypt at the moment and won't be for a couple of months so there won't be much progress, but as mentioned in the reply to Fallguy I am looking at possibly going with Mercruiser diesel power driving Bravo 3 sterndrives.

    Mainly in the hulls, as mentioned this is for motor yachts, but keeping noise to a minimum everywhere is something that will be working hard on with the shipyard owner for the motor yachts.

    For the dive boat the wheelhouse will be enclosed and aircon'd - partly because we want the wheelhouse to be lockable due to the electronics etc.

    For the motor yacht everything inside will be aircon'd - potentially even spaces like the engine rooms due to the brutal Red Sea heat.
     
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  14. Ad Hoc
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    Ad Hoc Naval Architect

    Yes and no.
    Like all things.. it depends!

    Noise, or sounds, is radiated as both airborne and structure borne...which give vibrations.
    But one does not equal the other...since vibration of air is very different from vibration of structure.

    Lets say the deck of a boat has a displacement of say 0.05mm (very small amount) - from a source - at a frequency of say 10Hz.
    You would notice it an it would be annoying. But it would require at least double the amplitude to start to cause damage.

    Or if you have a big lumpy engine, the structure doesn't move...but the sound from the engine is say 1kHz with an 90 dbA level....that's very annoying.

    So, you need to define what you're referring to in terms of noise or vibration and whether structure borne and/or air borne.
     
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  15. RSD
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    RSD Junior Member

    I should add that it makes sense that Egyptian shipyards progress into aluminium boat building as Egypt has a large aluminium smelter that is about 150 miles from the shipyard I am working with, and they can produce 5083 aluminium at very competitive prices as they get cheap electricity from the hydroelectric plant at the Aswan High Dam.
     
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