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Thread: New Boat 4 Sled

  1. #3821
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    Hi skip -

    There are lots of fiberglass mites (aka snapping shrimp) are well known to anyone that has spent a night in marina del rey - their incessant clicking sounds like something is outside the boat and eating through the hull. A bit of literature review determines that:

    1. While not directly a weapon, submarines could escape detection by hiding out in areas where the shrimp-created noise would hide or mask the submarine. A depth charge would have an affect similat to the shrimp's snapping behavior.

    2. Falling asleep to the crackly sounds of the shrimp is pleasant once you get used to them.

    3. The heat produced in the collapsing cavitation bubble does approach the heat of the sun - that was surprising to learn.

    4. The noise as a decibel reading is louder than a rocket launch.

    5. And the whole mechanism depends upon cavitation.

    Not sure about sperm whales - i have only encountered them mid-Pacific and not in southern california, so i will leave the whales out of my answer to your question.

    And cruising southern california is a.lot of fun!

    - rob

  2. #3822
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    The part of the story that I particularly enjoyed was that after our government spent lots of $$ to understand the sound made by snapping shrimp, they then recorded it and broadcast the sound from submarines to mask (i.e.hide) the sound signature of the subs. That’s the “weapon that helped win WW II.”
    Tom P.

  3. #3823
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    Quote Originally Posted by tiger beetle View Post
    There are lots of fiberglass mites (aka snapping shrimp) are well known to anyone that has spent a night in marina del rey - their incessant clicking sounds like something is outside the boat and eating through the hull. A bit of literature review determines that:

    1. While not directly a weapon, submarines could escape detection by hiding out in areas where the shrimp-created noise would hide or mask the submarine. A depth charge would have an affect similar to the shrimp's snapping behavior.

    2. Falling asleep to the crackly sounds of the shrimp is pleasant once you get used to them.

    3. The heat produced in the collapsing cavitation bubble does approach the heat of the sun - that was surprising to learn.

    4. The noise as a decibel reading is louder than a rocket launch.

    5. And the whole mechanism depends upon cavitation.

    Not sure about sperm whales - i will leave the whales out of my answer to your question.
    - rob
    Again, Beetle has answered the Quiz 100%. Congrats, Rob. Randall's book and Marianne's Macapuno awaits.

    1) In 1944 and 1945 (and perhaps at other times) the US Navy deliberately used snapping shrimp colonies and recordings as an acoustic screen to hide from underwater hydrophones and sonar in Japanese harbors, allowing U.S. subs to enter enemy harbors.

    2) As Rob observes, and likely DAZZLER and others remember, falling asleep to the "snap, crackle, pop" of snapping shrimp chorus while living aboard or cruising near shore is not an unpleasant experience.

    3) The snapping shrimp has two claws, a small pincer and an enormous snapper. The snapper, which can grow to half the length of the shrimp’s body, is not symmetrical. Instead, half of it is immobile and has a socket. The other half is mobile and has a plunger that fits into this socket. The shrimp opens the snapper claw with a strong muscle building tension until another muscle contracts, setting the whole thing off with incredible force.

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    When the plunger slams into this socket it displaces water that jets out at 105 feet a second (!), a velocity so high that its pressure drops below the vapor pressure of water. Tiny bubbles already present in the water suddenly swell in this low pressure, then collapse when the pressure climbs again.

    “You essentially create this cavitation bubble,” said coral reef biologist Nancy Knowlton of the Smithsonian Institute. “And when the bubble collapses, it generates that snap sound,” as opposed to the impact of the claws themselves making the noise.

    More importantly, the collapse of the bubble generates, for a split second, temperatures of 8,000 degrees Fahrenheit, nearly as hot as the surface of the sun, and also, oddly, a flash of light. The resulting shockwave bombards the shrimp’s prey, which, if it’s lucky, will die instantly because it is then dragged into the snapping shrimp’s burrow and consumed. It’s such a powerful blast that some snapping shrimp species use the shockwave to drill into solid basalt rock, snap after snap, to make a comfy little home.

    4. The sound of the snapping shrimp claw explosion has been measured at 210 decibels, loudest noise by a living thing except sperm whales clicks of 250 decibels that can be heard hundreds, even thousands of miles distant. (Decibels underwater are not equivalent to above water. But fun to note 210 decibels of the snapping shrimp is louder than the recent Space-X Falcon 9 rocket launch of 131 decibels inside the rocket fairing.)

    5. Cavitation is the snapping shrimp's weapon....if you had equivalent cavitation on your propeller, it would quickly melt. And an equivalent snapping shrimp's cavitation would blow your rudder 50 feet into the air.

    Did I mention the snapping shrimp, aka "pistol shrimp," is a member of the alpheidae family, a crustacean with an external skeleton? The whole operation is about as big as your big toe... Maybe BEETLE can find one on a dive...Beware, at very close range their pop can break the glass of an aquarium. *apparently this is an urban legend.

    6. The sperm whale answer is an intentional diversion, and not applicable....

    Here's a 2 minute NPR report: https://www.npr.org/2020/02/27/80974...mp-snap-louder
    Last edited by sleddog; 06-01-2020 at 10:40 PM.

  4. #3824
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    I have spent many delightful hours listening to them when I was boat based in Southern CA.

    Now, all the details of the mechanism is fascinating.

    Is there any reported instances where adverse impacts occurred when human got too close to the shrimp?

    Ants

  5. #3825
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    Quote Originally Posted by AntsUiga View Post
    Is there any reported instances where adverse impacts occurred when human got too close to the shrimp?
    Ants
    Hi Ants,

    DAZZLER may know better than I..but there are no reports of adverse impacts to humans from snapping shrimp. The whole sonic explosion, though intense, is very small.

    https://www.youtube.com/watch?v=QXK2G2AzMTU shows it in slo-mo.
    Last edited by sleddog; 06-01-2020 at 10:41 PM.

  6. #3826
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    The diver's boards talk about the feeling of being 'shot' by a snapping shrimp as the equivalent to being snapped by a rubber band - the surprise of being snapped is most mentioned.

    The Mantis Shrimp actually can draw blood if you are unlucky enough to have one puch at your finger with the 'hammer' portion of the raptorial claw; some species of these shrimp use the claw to strike hard-shelled invertebrates and crack open the exoskeleton, getting hit by that claw can break through the skin.

    And Skip - we'll have to get together one of these times and you can tell me how in the world you run across all these interesting things!

    - rob

  7. #3827
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    Quote Originally Posted by sleddog View Post
    DAZZLER may know better than I..but there are no reports of adverse impacts to humans from snapping shrimp. The whole sonic explosion, though intense, is very small.
    I’ve never encountered snapping shrimp while scuba diving. But like Rob, I’m reminded of Mantis Shrimp, which are neither a mantis or a shrimp. Mantis shrimp are territorial creatures and have been known to exhibit aggressive behavior toward intruders. Their specialized club-like appendages fold to beneath their body and resemble a praying mantis. They use their appendage to punch their pray at a speed 50 times faster than the blink of an eye with a force that can easily break the shell of a crab or mollusk. I’ve heard stories of mantis shrimp breaking underwater camera lenses.

    I’ve only seen one mantis shrimp while diving in tropical waters and he/she retreated into it’s hole before I took this picture. Those lobe like protrusions are the eyes.
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    Last edited by Dazzler; 06-02-2020 at 10:23 AM.
    Tom P.

  8. #3828
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    I am thoroughly enjoying this review of marine invertebrates! My MS is in Marine Science, with an emphasis in local benthic invertebrates, particularly mollusks.
    S-2 7.9: "Wildcat of Loch Awe"
    1968 Selmer Series 9 B-flat and A clarinets
    1962Buesher "Aristocrat" tenor saxophone
    Piper One Design 24, Hull #35; "Alpha"

  9. #3829
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    Several ship captains I know have had answers from finders of their messages in bottles set adrift at sea.

    But if you haven't visited Randall's Figure 8 Voyage blog recently, there's a terrific message in a bottle story there. Thanks to PHILPOT for this info!

    http://figure8voyage.com/blog/

    Has anyone on this Forum had a message in a bottle returned, or equivalent? Years ago, in the NE tradewind belt, I set one adrift anchoring a stick, paper, and cloth kite on cotton string. When last seen, the bottle was gaily skipping along at about 2 knots being pulled by the bottleneck by the kite, distant in the popcorn clouds.
    Last edited by sleddog; 06-03-2020 at 07:49 AM.

  10. #3830
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    On the subject of Randall Reeves and his Figure 8 Voyage, be sure to listen to the Ben Shaw Out The Gate Sailing podcast interview #29 with Tony Gooch (former owner of MOLI and circumnavigator in his own right) and the three interviews with Randall. Impressive.
    Tom P.

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