Things That Go Bump in the Night

[StoneCrab]

My tankage is all metal with straight sides. I think they call that noise "oil canning". Anyway, the sides of the tank will have a little flex and then pop to being flexed in the other direction. It makes a low pitched pop noise.

Temperature, liquid level, probably barometric pressure, can all affect the forces on the side of the tank. The movement in the tank wall isn't much and not harmful, but it does make a noise when it happens... which is only occasionally for me.

If you have rounded storage tanks, check your galley for suspect tins with flat sides or even a top or bottoms which might have popping.

If the temperature drops a lot in the night the noise could be from other material shrinking with the temperature change. Sounds odd, but everything grows and shrinks with temperature. Wires, hoses, pipes anything relatively rigid can store the energy from the size change until it overcomes the friction on whatever is holding it making a pop noise.

Radiators in a house are a good example. Most make noise as the system heats up. This is why.

For houses with forced air, if you look at the sides of the duct work, it will normally have a crease looking like an "X" on the sidewalls. This is a slight break line formed by bending the metal a few degrees to keep the amount of oil canning to a minimum. Without the X, the sides will flex everytime the system comes on.

Another example is your car. Listen to all the noise it makes after you turn it off. It will make ticking noises for a long time until everything is at the same temperature.

On the other hand, it might be the ghost of a pirate that has come to visit. When you are really really sleep deprived on a passage, he might show his face or speak to you.

Good luck.

[SV Aquavit]

My aluminum fuel tank flexes with a thud when temp changes. Also does the same flex / thud while topping off fuel. That's how I know I'm close to full!

[slug]

Originally Posted by Howler

This is a strange one. When overnighting onboard our 41 foot sloop, there’s invariably a loudish “thump” sound that occurs once every night just around dawn. The first tine it happened I thought someone hit us but nobody for miles around. I can’t tell for sure but it sounds like it’s coming from above, maybe as if you plucked a shroud or gave the mast a wack.

I’ve inspected the rigging, expecting to discover the mast was standing thanks to a single cotter pin or something. Everything looks sound. The boat’s only in its third season.

It’s a mystery. What’s causing it? Why every day? Why only once a day? Why at that time?

The only thing that comes to mind is thermal expansion. Something warms up faster than something else, on deck or in the standing rigging, when the temperature starts going up toward daybreak.

Anybody else experience this? Any ideas what it could be?

Thanks!

Fish whack into the bottom with a thump

[Howler]

Originally Posted by jim King

Are you on a mooring ball? Is there a tidal shift at about the time of the thump?

No, we're anchored. And we're on the Great Lakes, so no tides (and no salt, no sharks, no hurricanes, blablabla).

[Uplander]

Sounds to me like dawn breaking

[mjscottinnc]

One evening at a new anchor spot just after sun down there was the sound of a motor running. Spend 10 minutes going from cabin to cabin searching, found nothing. eventually I turned off all electric, but the motor continued to run, it seemed loudest in the Vberth. By complete accident I pushed a book off the berth and it hit the floor with a loud boom. The motor had stopped, and then gradually picked up in intensity again. Hung over the side of the bow to confirm it was coming from 12 foot below the waterline. Boat hulls make great amplifiers when your inside them. As best I can tell the motor had to be a crab nursery. Food for thought.

[Howler]

Thanks for all the creative replies... dolphins, carp, big birds, crab nurseries, dawn breaking, oil tanking, thermal expansion and ghosts. I’m narrowing it down to thermal expansion and ghosts, but only because we have no dolphins, crabs, etc, on the Great Lakes.

[er9]

I have a very regular evening lightning bolt cracking sound. It sounds like a mini lightning bolt is best way I can describe it. Always located in one of two or three locations somewhere along the cabin top and /or along the sides of the cabin. Seems to happen when the day is cooling g down in the evening but sometimes random. It seems to definately be from thermal expansion/contraction as there is zero signs of damage anywhere. Loud enough to jolt me out of my seat sometimes.

[gamayun]

Originally Posted by er9

I have a very regular evening lightning bolt cracking sound. It sounds like a mini lightning bolt is best way I can describe it. Always located in one of two or three locations somewhere along the cabin top and /or along the sides of the cabin. Seems to happen when the day is cooling g down in the evening but sometimes random. It seems to definately be from thermal expansion/contraction as there is zero signs of damage anywhere. Loud enough to jolt me out of my seat sometimes.

I also have this "bolt" type popping sound on my boat. Thought at first it was settling after the first time I had hauled her because I hadn't noticed it before. I now think it is caused by expansion due to heat of the day followed by cooler evenings. I think it's somewhere in the fiberglass, maybe where it meets a bulkhead. It doesn't seem to happen year round, but I haven't kept any records. Just got used to it, I guess.

[Ianau]

Thermal linear expansion of alloy mast acting on deck or chainplates?


Way to check would be to loosen off the backstay as the backstay to forestay would form the bowstring.

[billgewater]

If you have synthetic standing rigging then the thermal expansion/contraction properties are considerably different to aluminium. Some really large plastic windows also have different thermal expansion properties to other materials.

Have you asked others in the area if they have a similar problem as an answer may help eliminate possibilities such as dolphins, dead men banging the insides of sea chests etc.

If it was a large bird, they usually leave a calling card - all over the deck.

However it does sound like a relaxing of something under tension or compression, so it is probably a thermal.

Do you have any heaters, air conditioners, built in freezers? i.e any thing that may induce or create hot or cooler spots on the structure?

Is it possible that with tide changes that the boat may move across and touch or bounce off something on the bottom? A dragging chain getting caught on the bottom? Sounds unlikely but if you check the boat's orientation before and after the noise and check the bottom with the scanning sounder, something may be revealed. The obvious clue is does the incident time shift every day with the tide change progress.

Finally, does this event have a past history with the boat .i.e. has it occurred elsewhere or at previous times. i.e. is it unique to where you are moored?

We are all waiting for your ultimate discovery.

[GILow]

Originally Posted by Howler

Thanks for all the creative replies... dolphins, carp, big birds, crab nurseries, dawn breaking, oil tanking, thermal expansion and ghosts. I’m narrowing it down to thermal expansion and ghosts, but only because we have no dolphins, crabs, etc, on the Great Lakes.

Yeah, I’m with the ghost theory. But, and this is important, a punctual ghost.

[Howler]

Originally Posted by billgewater

If you have synthetic standing rigging then the thermal expansion/contraction properties are considerably different to aluminium. Some really large plastic windows also have different thermal expansion properties to other materials.

Have you asked others in the area if they have a similar problem as an answer may help eliminate possibilities such as dolphins, dead men banging the insides of sea chests etc.

If it was a large bird, they usually leave a calling card - all over the deck.

However it does sound like a relaxing of something under tension or compression, so it is probably a thermal.

Do you have any heaters, air conditioners, built in freezers? i.e any thing that may induce or create hot or cooler spots on the structure?

Is it possible that with tide changes that the boat may move across and touch or bounce off something on the bottom? A dragging chain getting caught on the bottom? Sounds unlikely but if you check the boat's orientation before and after the noise and check the bottom with the scanning sounder, something may be revealed. The obvious clue is does the incident time shift every day with the tide change progress.

Finally, does this event have a past history with the boat .i.e. has it occurred elsewhere or at previous times. i.e. is it unique to where you are moored?

We are all waiting for your ultimate discovery.

Thanks. We can rule out animals and tides (Lake Ontario). It does occur at different anchorages. The only appliance would be the standard fridge. I will ask others in the area but things are pointing increasingly to the varying materials of the deck or standing rigging when the temperature changes

[rslifkin]

Howler, I just noticed you're in Rochester. Don't rule out a fish problem. It's probably not carp this late in the season, but in late May / early June you'll see some big carp jumps in the marinas. And they do hit boats occasionally. The first time I heard one thud against my hull I had a really good "what the heck was that!?" moment.

Realistically, it's most likely thermal expansion somewhere on the boat. We've had a lot of hot sun and still cool-ish nights lately.

[billgewater]

Originally Posted by GILow

Yeah, I’m with the ghost theory. But, and this is important, a punctual ghost.

AND, Megan Long has written a book on the Ghosts of the Great Lakes.

"Ghosts of the Great Lakes: More Than Mere Legend " (Amazon).

There. We have the definitive answer. And these ghosts actually smell as it appears as though they are always, as you have observed, on THYME. Scent to the bottom. They can be detected by smell. Who nose? And they also wander around. One was described as "Aroma".