NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Noisy Sea Surface
From: Trevor Kenchington
Date: 2003 Nov 15, 12:30 -0400
From: Trevor Kenchington
Date: 2003 Nov 15, 12:30 -0400
Keith, Thank you for the extra details. By "relatively high frequency", I only meant that it is not the sort of low-frequency (on the edge of human hearing) which does seem able to transmit from water to air if the sound waves strike a calm surface perpendicularly. (I don't even have any hard evidence that sound can be transmitted from water to air with reasonable efficiency under those circumstances but I think it can). It is interesting that what you have heard happens with a clean hull and sounds so like bubbles. Could it be bubbles? Eel grass can be so dense that its respiration at night depletes dissolved oxygen to the point that it can kill animals in the grass beds. Perhaps by day it might saturate the water with oxygen. Could that come out of solution when it contacts the surface of the hull, as the surface water cools at night? Alternatively, could it be gas released from bottom sediments as the tide falls (reducing pressure at the seabed)? Release of seabed methane is by no means uncommon. I'm groping for an explanation but also trying to illustrate the wide range of phenomena which might be responsible. Trevor Kenchington You wrote: > To clarify - I have only heard this noise when I have been down below in > a boat. The noise appears to come from all parts of the hull below > water. I can be (almost!!) certain that the noise appears even on a > newly-antifouled boat, so feeding on algae could be contra-indicated by > that. > > My boat is a cold-moulded wooden boat with epoxy-glass outer skin. I > have not heard the noise from within a steel hulled boat, but I have > from within a glassfibre boat. I assume this is because I haven't spent > much time in metal boats. > > The noise is not very high frequency by standard human measures, almost > exactly what I make by making a clicking noise in my mouth; and the best > description is clicking - certainly each sound is not a scrape (ie, each > noise is short); I mentioned explosive bubbles because that really is > the best description. Like having a champagne supply under the boat. > Keith Williams > > -- Trevor J. Kenchington PhD Gadus@iStar.ca Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555 Science Serving the Fisheries http://home.istar.ca/~gadus