Visit our Popular Forums

Howler · 06-07-2020, 09:33

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!

rslifkin · 06-07-2020, 09:38

I always get a few little pops as things expand from heat when the sun hits the boat in the morning. More so after a cool night. And we get a few pops in the evening as things cool after a hot, sunny day. No leaks or other known issues, so I just call it normal for this boat.

wingssail · 06-07-2020, 10:03

Quote:

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!

Yeah, I've got one of these thunks. Mine happens in late afternoon on hot days, from a specific spot on deck, but there is nothing there. So? A mystery.

chris mac · 06-07-2020, 17:03

An odd longshot, but if there is a breaker on your solar panels there could be an audible click or thunk from it activating.

Howler · 06-07-2020, 17:50

Quote:

Originally Posted by chris mac

An odd longshot, but if there is a breaker on your solar panels there could be an audible click or thunk from it activating.

Good thought but we don't have solar panels and it's a deeper sound than a breaker. Thank you though.

GILow · 07-07-2020, 03:00

I was troubled by an odd thump that I thought was something hitting the hull, and it turned out to be dolphins slapping the water to stun the fish. Probably not the cause in this instance, but a possibility?

Tortuga's Lie · 07-07-2020, 03:16

You could loosen up on the shrouds just a touch and see if that makes a difference, could be that the rig is over tensioned.

Howler · 07-07-2020, 03:31

Quote:

Originally Posted by Tortuga's Lie

You could loosen up on the shrouds just a touch and see if that makes a difference, could be that the rig is over tensioned.

They are pretty tight. I'll try that. Thanks.

Howler · 07-07-2020, 03:36

Quote:

Originally Posted by GILow

I was troubled by an odd thump that I thought was something hitting the hull, and it turned out to be dolphins slapping the water to stun the fish. Probably not the cause in this instance, but a possibility?

I wish that were the answer, but we haven't spotted any dolphins on Lake Ontario lately. And it's literally one thump, once a day. Not sure dolphins are that consistent!

Similar story... We do have huge salmon that get sidetracked into our marina during their trek up the river. The first time one jumped just outside the boat, it made a very loud sound.

gansett · 07-07-2020, 05:13

Could the sound be the departure of a large bird that had been roosting in the rigging over night? They usually begin their daily routines at dawn.

jim King · 07-07-2020, 08:58

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

wingssail · 07-07-2020, 09:27

Quote:

Originally Posted by Tortuga's Lie

You could loosen up on the shrouds just a touch and see if that makes a difference, could be that the rig is over tensioned.

Well, that would support the theory that it is some sort of thermal issue, since possibly the shrouds (or mast), are contracting as they cool and that relieves some pressure somewhere in the boat, possibly the deck, and something shifts as the pressure releases (like a tectonic shift in the earth, resulting in an earth quake, so you're having mini earth quakes on your boat) but honestly, on my boat I'd put up with the creaks and groans rather than ease the tension on your shrouds. Assumedly they have been tensioned properly, and easing them would make them somewhat slacker than ideal. Not what I'd do.

BTW, on my boat the sound comes at the heat of the afternoon, when most things have expanded, not contracted.

edit: Just looked it up, aluminum contracts and expands twice as much as stainless steel. So maybe when your mast contracts as it cools it is relieving pressure on the rig, as implied by Tortuga's Lie, and, yeah, something in your beneteau shifts.

Sirago · 07-07-2020, 09:42

I heard bumps in the night when the wind picked up and the boat swung on her anchor rode. The roller in the anchor holder would slap back and forth with tension on the rode. If the sound goes away we are dragging the anchor.