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As a cruiser we encounter scores of distinctive and sometimes unusual circumstances and many times they are not what we assume they are. We had dock mates a few years ago who were complaining to me about the galvanic corrosion on their vessel's submerged zincs while visiting a local marina. "It was so severe, you could actually hear the decomposition taking place; we'll by no means go to that marina for a second time." I just smiled and nodded my head. As a boater, when you reach the warmer waters in Florida and further south, you may well hear noisy crackling sounds coming from under your boat's hull at night time. The sound can be surprising if you don't understand what you are hearing; is the boat breaking apart you think? The sound might be described as cooking bacon in a frying pan or the crackling of dry timber burning. On the docks, it is frequently thought that these noises were purely krill feeding on the marine grass on your boat's hull. Not true say marine researchers, it's the sound of snapping shrimp. The shrimp, Alpheus heterochaelis, is a tiny one inch crustacean that lives in the shallow waters of sub tropical seas. It has two claws', one larger than the other, that it uses to stun its prey, for example very small crabs, by snapping the biggest claw close. Researchers have, merely a short period ago, discovered how these small shrimp emit so much noise. At first they thought it was the clicking of the shrimps' enlarged claws. And it is ... sort of. It is now reported that the surprising snap comes not from the clap of the claw itself but from a bubble created by the claws' fast closing action. When the claw clamps closed, a spray of water emerges from an opening in the claw, generating a bubble. As the energy stabilizes, the bubble collapses with a loud noise; it's the cavitation from the water created by the quick closing. Just like the cavitation from your boat's propeller, the water from the snapping claw makes very small cavitation bubbles. As soon as the bubbles burst, the telling snap is created. The total progression, which was studied with the use of fast photography equipment and sound equipment, purportedly happens within 300 microseconds. In addition, a burst of light also takes place when the bubble explodes. The flashing occurrence is thought to be like sonoluminescence, which is defined as the giving off of brief bursts of illumination from imploding bubbles in a fluid when excited by noise. The researchers have correctly labeled the shrimp's snapping as shrimpoluminescence. The scientists were not capable of seeing the bursts of light with the naked eye but they can't entirely discount it. The possibility exists that people very near to the shrimp when the bubble collapses and whose vision is well used to the underwater darkness may be able to witness it. The light flashes seem to have no real importance, the scientists say, but are a side-effect of the bubble collapse. The radiant release is, nevertheless, indicative of the extreme situation within the bubble at bursting and consequently shows the significance of the incident. In tepid sub tropical waters, these tiny shrimp are abundant and noisy - so noisy they will keep you up at night time. Snapping shrimp allegedly snap at 200 decibels, way above the human being audible range pain threshold. So the next time you're aboard on the hook, listening to the noise under your vessel, think of the thousands of snapping shrimp in the water beneath you, busily directing their own symphony while stunning their prey, defending their territory, and communicating with other critters in the deep. Mike Dickens, the author, is a live aboard boat owner and owner/Broker of Paradise Yachts in Florida USA. Paradise Yachts offers used quality yachts to customers worldwide. National and international sales. We ship Used Trawlers, Motor Yachts and Cruisers worldwide. Located in Florida, USA. 904/556-9431
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snapping shrimp, galvanic corrosion, zincs,
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