View Poll Results: Would you be interested in buying discounted goods from a catalogue (20,000+ products) at a marina?

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  • Yes I would!

    2 66.67%
  • No I would rather pay more at a local chandler

    1 33.33%
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  1. #21
    ArthurJStoatfondler's Avatar
    ArthurJStoatfondler is offline Registered User
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    Default Re: er not the props

    tcm - Not prop noise from your own boat! Prop noise from a passing boat.

  2. #22
    Swagman's Avatar
    Swagman is offline Registered User
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    Default Sad Trend

    Hope this is not taken wrongly but it seems to me more and more threads turn into respondants commenting upon each others expertise or knowledge - as opposed to providing good advice to the person who asked the orginal question.

    I for one thank BrendanR for publishing the link to the sounds I've certainly experienced - and in doing so clarifying for me the source.

    So come on guys - why not put all the handbags away or at least stop swinging them at one another - and get back to using this forum for what it is intended - practical advice.

    Cheers
    JOHN

  3. #23
    tcm is offline Registered User
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    Default Re: er not the props

    ah understood.

    But i get this at anchor when there are no other boats for miles - or the same noise in marina if other boats are going past a fair bit eg mid-morning. INothehr words not dependent upon lots or zero nerarby boats. It is a reasonably constant-volume chompity chompity (in the same as are ciccadas on a warm night in the med) - whereas a passing boat noise wd come in and go away? An explanation such as a lot of small creatures fairly nearby (ie on the hull) make sense.

  4. #24
    ArthurJStoatfondler's Avatar
    ArthurJStoatfondler is offline Registered User
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    Default Re: \'Snap crakle and Pop\' noise from under hull?

    It's propellor noise from other boats and it's easy to prove. Next time you are on a boat which is anchored, tied up in a marina or wherever, it doesn't matter as long as the sea is calm, do the following:

    1 Wait until a boat under power passes within 50 to 100 yards of you.
    2 As the boat passes, get into the bilge of your boat where you can see the inside of the hull below the waterline.
    3 Make sure there is no extraneous noise.
    4 Listen to the crackling sound through the hull.

    It happens every time and this is the noise you hear at night when it's quiet, as boats pass. It seems to be more obvious on fibreglass boats, presumably they transmit the sound better.
    I have no explanation, only a theory that it's cavitation noise, and I can do no more than tell you its source.

  5. #25
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    Default Re: Sad Trend

    Agree about the sad trend ...

    The link that BrendanS posted has both snapping shrimp and a diesel engine 650 yards away - with snapping shrimp in the background.

    I have heard the sound as well, both in Med and Caribbean, and assumed it was creatures of some kind - fish snapping at coral, crabs etc. I also assumed that it did not need to be right next to the boat (i.e. could be up to 50 metres away or more) because a) noise propogates so well in water b) the sound was so constant and c) there seemed to be so many sources.

    I am glad to have my suspicions confirmed. Snapping shrimp is the explanation I will give to others from now on.
    Apartment for rent in Klosters, Switzerland http://goo.gl/HKIcgK

  6. #26

    Default Naughty

    [ QUOTE ]
    I don't care how offended you are

    [/ QUOTE ]

    Offending people is definitely not permitted. Surely you knew that?

    Funny thing really. Regular outbursts in the Lounge against political correctness, most of which represents an attempt, however misguided, to avoid giving offence, combined with outrage against anything that might give offence.

    There's nowt so queer etcetera [img]/forums/images/graemlins/confused.gif[/img]

  7. #27
    Swagman's Avatar
    Swagman is offline Registered User
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    Default Engine Noise?

    Can't help myself in adding this fact - to try and put the 'it's an engine / prop noise' view into perspective.

    I've heard this noise all night parked up in a coral atoll with closest civilisation (ie other island 350 miles away) and never another boat of any size in sight.

    Guess others will now say it must have been a submarine parked up the other side of the atoll on tickover...........

    Hopefully enough said.

    JOHN

  8. #28
    tcm is offline Registered User
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    Default Re: \'Snap crakle and Pop\' noise from under hull?

    um, with respect and logically speaking your test proves no such thing. The noise described could be present before and after the boat passes - but your test requires one to listen only as and when a boat passes - it sets out to confirm the pre-decided cause.

    A better test is to wait until there are NO boats passing and then listen - in other words one shoud try and prove the hypothesis by attempting to *disprove* it. Hence, essentially, "the exception proves the rule".

    In this case the lack of boats passing on even just ONE occassion would prove it cannot be prop noise. Others do report the noise without any boats moving nearby.

    If it was cavitation then it would be surely accompanied by the rythm of the props. And would there *always* be cavitation if a prop turns, even at very low speed? And surely, wouldn't the frequency/pitch or amplitude/volume of the noise vary quite dramatically if it were prop noise? The noise made by a 6inch diameter prop 20mteres away ould not be the same as a 1metre prop say 75 metres away. Yet the noise made by throng of nearby tiny ainmals would be always about the same volume and pitch - as this noise is?


  9. #29
    ArthurJStoatfondler's Avatar
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    Default Re: \'Snap crakle and Pop\' noise from under hull?

    tcm you may be right.
    What I do know though, is that the sound occurs when boats pass. I don't know the maximum range that it can be heard from, but I do know that I've never heard it in UK waters or the Med unless boats are passing. Having said that, I can't be spending too much time with my head in the bilge listening.
    I have heard this in The Seychelles without boats passing and will accept that in that case it may be Snapping Shrimps as they are found in tropical waters, but I'm still not convinced that they can be heard without the aid of a hydrophone.
    Mantis Shrimps which are snappers have been found in UK waters but I doubt in sufficent numbers to be heard without a hydrophone.
    So after years of puzzling about this I still think it's passing boats as far as UK and Med are concerned. If anybody can prove that it's not, then I'd be very interested if they would post their views as I'd like a definitive answer.

  10. #30
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    Default Re: \'Snap crakle and Pop\' noise from under hull?

    So, to follow the logic, tropical waters may have dolphins but after years of puzzling what the identical-looking creatures in the UK might be I've concluded that the grey bow-leaping things must be mutant binbags. Please prove to me that they're not.

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