Crackling Sound Below the Waterline on Steel Boat

[Greatest Lakes]

I'm my area, we get a thumping noise. It's carp bouncing off the side of the boat to help lay eggs when spawning. If someone has a bubbler running to break up ice in early spring, that's a humming noise. I spent an hour trying to figure out where I had a pump running, it's that loud.

[bumpman]

Don't forget Sea Robins and their cousins. Sometimes sound like underwater barking or quacking. Especially at night the marine world is alive with sound, just like all the noisy critters on land.

[Scorpius]

Shrimp. If you are in a steel boat that hasn't been foam sprayed (insulated) inside, you are in a large echo chamber. Anything going on outside under water will be greatly amplified.

[Don C L]

We've got some noisy shrimp on this coast too! They're all over.

[tamicatana]

For most all noise in the sea, a good reference:

https://dosits.org/

[Tupaia]

Wow 4700 degrees - headline - shrimps not only kill but cook their food before eating it.

Nature never ceases to amaze us.

[mporter]

Originally Posted by Bowdrie

It's the Polyestermites eating away at the gel coat.

In this case they are gnashing their teeth because the boat is steel!

[blueskymessenge]

Probably pistol shrimp if it is not a machine gun sound but a loud popping.
These beasts are the loudest of the creatures, used by the Navy in WW2 as sound masking for subs (yea unbelievable) but this video will show you why and what that noise is most likely. They live just about everywhere and the knock sound they make is actually quite loud. Harmless but loud.

https://www.youtube.com/watch?v=ZJm0npZAk3o

[jimellifritt]

Shrimp

[TabbyCat]

Originally Posted by KelseyB

Thanks everyone- really glad to hear the consensus is "marine life of some kind"! That's what I'd seen as answers elsewhere but given how fresh the bottom job is, I just wanted to confirm!

I agree- shrimp- and especially since you have a new bottom job. I know that sounds odd, but every time we do the bottom and re-launch , we notice we have more shrimp popping sounds than when the paint was old. You would think it would be the opposite....?!

[RedFeather]

Originally Posted by tamicatana

Alpheid shrimp:

https://en.wikipedia.org/wiki/Alpheidae

FTA: "Snapping effect

The snapping shrimp competes with much larger animals such as the sperm whale and beluga whale for the title of loudest animal in the sea. The animal snaps a specialized claw shut to create a cavitation bubble that generates acoustic pressures of up to 80 kilopascals (12 psi) at a distance of 4 cm from the claw. As it ejects from the claw, the bubble reaches speeds of 100 km/h (62 mph).[citation needed] The pressure is high enough to kill small fish.[9] It corresponds to a peak pressure level of 218 decibels relative to one micropascal (dB re 1 μPa), equivalent to a zero to peak source level of 190 dB re 1 μPa m. Au and Banks measured peak to peak source levels between 185 and 190 dB re 1 μPa m, depending on the size of the claw.[10] Similar values are reported by Ferguson and Cleary.[11] The duration of the click is less than 1 millisecond.

The snap can also produce sonoluminescence from the collapsing cavitation bubble. As it collapses, the cavitation bubble emits a short flash of light with a broad spectrum. If the light were of thermal origin it would require a temperature of the emitter of over 5,000 K (4,700 °C).[12] In comparison, the surface temperature of the sun is estimated to be around 5,772 K (5,500 °C).[13] The light is of lower intensity than the light produced by typical sonoluminescence and is not visible to the naked eye. It is most likely a by-product of the shock wave with no biological significance. However, it was the first known instance of an animal producing light by this effect. It has subsequently been discovered that another group of crustaceans, the mantis shrimp, contains species whose club-like forelimbs can strike so quickly and with such force as to induce sonoluminescent cavitation bubbles upon impact.[14]

The snapping is used for hunting (hence the alternative name "pistol shrimp"), as well as for communication. When hunting, the shrimp usually lies in an obscured spot, such as a burrow. The shrimp then extends its antennae outwards to determine if any fish are passing by. Once it feels movement, the shrimp inches out of its hiding place, pulls back its claw, and releases a "shot" which stuns the prey; the shrimp then pulls it to the burrow and feeds on it.[citation needed]

When in colonies, the snapping shrimp can interfere with sonar and underwater communication.[4][15][16] The shrimp are a major source of noise in the ocean[4] and can interfere with anti-submarine warfare.[17][18]"

This is by far the most fascinating thing I’ve read in a long time.

[1Jazzsailor1]

It's nothing to worry about...it's just Krill

[nofacey]

Lol…..I went nuts went this started on near new DreamCatcher - thought the spray foam mover my steel hull was separating and I was about to have a massive mess on my hands - we were travelling south down the US Westcoast into Mexico & it was getting worse & worse - definitely lost sleep listening to it.

Then I mentioned it to a seasoned skipper in LaPaz, and he laughed before taking me down into the bilge on his large fiberglass yacht; “does it sound like this? “ “YES” said I
“Tiny shrimp cleaning your hull, drives everyone nuts till they figure it out”

Goes hand in hand with being chased by the moon for newbie skippers. 😂

[Lightwave99]

What you are hearing is not a cusk eel. It is tiny tiny little shrimp that eat the stuff on the bottom of the house. We had it the whole time we were in the sea of Cortez and we certainly were not staying at marinas very often. At one Anchorage on the east side of the sea of Cortez south of Mazatlan Garett dove on the hall in his wetsuit and scraped them off. They are really tiny and creepy but they do make this constant crackling noise. He was covered in them when he came up from cleaning them off the bottom of the hull. As others have said they must eat what is on the bottom of the hull.

[Lightwave99]

PS to previous reply: our boat is a catamaran with fibreglass hulls.