Crackling Sound Below the Waterline on Steel Boat

[KelseyB]

So. I have noticed that there is a crackling sound coming from outside my boat below the waterline and I am very curious as to what it is. Sounds like Rice Krispies—I really don't have any other descriptors for it.

I have a 30-foot steel boat, and I am very nervous about electrolysis because she's in an industrial city with (probably) a lot of stray currents running around. She has plenty of zincs, but it's always a fear. I read some other posts saying it's shrimp and other marine life feeding on the bottom, but my boat was launched exactly 1 week ago with a fresh bottom job. The first time I launched the boat with a fresh bottom job, I don't remember hearing any crackling sounds. I first heard them 8 months after that first launch, when there was some algae on the bottom and the boat was in Florida at the time, so I didn't have any issue dismissing it to marine life. But now, with a fresh bottom job and at a dock in a river that isn't particularly "teeming with life," I am a bit suspicious. Anyone have any idea what the sound could be? Should I be worried?

[NaClyDog]

Believe it or not, my money would be on shrimp.


We had this occur on a charter and everyone told is not to worry, it was "just shrimp".

[misssherry]

It happens on fiberglass boat too. Apparently the sound comes from shrimp and crabs.

[redneckrob]

Originally Posted by KelseyB

So. I have noticed that there is a crackling sound coming from outside my boat below the waterline and I am very curious as to what it is. Sounds like Rice Krispies—I really don't have any other descriptors for it.

I have a 30-foot steel boat, and I am very nervous about electrolysis because she's in an industrial city with (probably) a lot of stray currents running around. She has plenty of zincs, but it's always a fear. I read some other posts saying it's shrimp and other marine life feeding on the bottom, but my boat was launched exactly 1 week ago with a fresh bottom job. The first time I launched the boat with a fresh bottom job, I don't remember hearing any crackling sounds. I first heard them 8 months after that first launch, when there was some algae on the bottom and the boat was in Florida at the time, so I didn't have any issue dismissing it to marine life. But now, with a fresh bottom job and at a dock in a river that isn't particularly "teeming with life," I am a bit suspicious. Anyone have any idea what the sound could be? Should I be worried?

It's the shrimp. They don't need to be feeding on your bottom, just near your bottom for it to be way louder than you would think. Electrolysis is not a noise producing event at stray current levels.

[HankOnthewater]

Hi KelseyB
I know how you feel. For many weeks I worried that my then ferro boat was rusting and the crackling noise was caused by minute cracking in the concrete by expanding steel reinforcement. Hull remained sound and I had that boat for 20 years. And noise was nearly always present.
But alas, the above posters are right, caused by waterlife. Sleep well.
zzzzzzz

[MicHughV]

I had a steely for 15 years. That crackling sound is crabs, not necessarily big crabs..but small one's like fiddler crabs..as well as shrimp.....they feed on the bottom and also on tiny detritus on your hull.
I only hear it when I'm at a marina....I don't hear it when I'm anchored somewhere.

You get used to it after a while, but's it's nothing to be concerned about.

[Ferrity]

Another possibility is cusk eels. I encountered them in North Carolina. A YouTube search will reveal audios to compare to the sound you are hearing.

[Bowdrie]

Originally Posted by misssherry

It happens on fiberglass boat too. Apparently the sound comes from shrimp and crabs.

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

[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]"

[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!

[SailFastTri]

Does it sound like cusk eels?

https://www.youtube.com/watch?v=87MIHnqYilQ

[MicHughV]

I never realized the abundance of shrimp at my marina until I noticed local fisherman throwing cast nets around the boats and coming up with a lot of shrimp..smallish one's...but a lot of them...good for bait..

[PLANET EXPRESS]

https://dosits.org/animals/sound-pro...roduce-sounds/

[goboatingnow]

Sea life, I hear it every night

[s/v Jedi]

It’s called krill and indeed, small shrimp. It’s what’s in your hair after scraping the bottom underwater.
https://en.wikipedia.org/wiki/Krill

The knocking sound is much larger crustaceans and this can be loud enough that you think something hit you.