I "misspoke" in an earlier posting about the Snap, Crackle, Pops we sometimes hear on MicMac's hull when we're below deck. It's a minor tapping, but it drives me to earplugs when I want to sleep.
I was half-right when I attributed it to shrimp-like krill critters. A Beaufort, SC diver added even more info than what I just found in one of our cruising guides. He told us that he sees these "grass shrimp" under hulls as he scrapes off barnacles and other "under-boat growth." He laughed when I asked if these shrimp are eating the algae, and said "that would put me out of a job."
The cruising guide says it's the sound of snapping shrimp. It seems that these little guys eject water jets as their claws snap shut at 62 mph. Really--not at 60 or 65, but at 62 mph. There's a bit of trivia for your next onboard happy hour!
The technical term is "cavitation" or similar to the the water jets formed by boat propellors. Scientists still don't know if they do it to stun their prey or to attract a mate. Whatever it's called--or whatever the reason--it's a distraction to my sleep.