Help with deciphering soft knocking sound

[bravenewworld]

Check all of the following:

1. Rudder harmonic vibration,
2. Anchor chain responding to current and wave action: at the locker or pullpit,
3. The pulleys in the helm cable or chain connections,
4. Shrouds, stays or halyards contacting a Bimini canvas,
5. A sheet in tension and release around a winch, cleat or padeye,
6. Mast head position of halyards as they pass over the sheaves,
7. Stored items moving rhythmically in storage lockers or lazarette,
8. Torsion occurring in the deck/hull interface.

All of these cause a muffled repeating clunking sound in my experience.

[TrentePieds]

When she came to me, TrentePieds had a weeping hose joint downhill from the Jabsco diaphragm pump next the potable water tank. Pump was mounted solidly - no rubber feet - on a tiny plywood platform glassed to the hull. "Thump, thump". Silence. "Thump, thump". Silence. "thump..." Took me ages to find it! As the pressure dropped due to the weep, the pump would thump. Two strokes was all it took to get the pressure up again to last for fifteen or twenty seconds. Hauled the whole hose run outta the bilge and found a hose joint in a place that was out of sight the way the hose was mounted under the sole.

TrentePieds

[reed1v]

Originally Posted by challis0124

I am not sure where this post belongs because I'm not sure exactly what the culprit is, so I'm hoping someone here can shed some light.

I am currently on an Island packet sailboat at anchor in an area with strong current and tide shift. I just noticed this evening there is a soft rhythmic knocking coming from somewhere on the boat...I can't pinpoint its location it sound like it's everywhere and nowhere. But it's continuous. Every few seconds it knocks 5 times then stops for a few seconds and starts up again.

I don't know if it's something on the deck( though I have checked all rigging and nothing that looks or sounds like this.) I live aboard my boat so am very attune to her sounds. I don't think it's anything on the engine, though I have heard prop shaft could cause something tho I'm not sure that's it either...maybe anchor chain ( though I doubt it). It almost reminds me of a woodpecker

Maybe a ghost

Any thoughts or if you have ever experienced this ? Much appreciated!

Check under the floor boards, especially up forward. You probably have something stored under there that is rocking back and forth. We found an anchor kettle under our forward floor boards that use to give a thumping sound when underway.

[barnakiel]

I had this woodpecker thing when a turnbuckle cover (we use plain pvc pipes) moved every time the boat rolled a bit.

When there is much current, the sound can come from the steering gear or from anchor rode elements (e.g. taut nylon warp will vibrate in the current).

b.

[CLady]

Perhaps something is hung up on your prop or shaft that thumps the hull in the current.

[Cadence]

Originally Posted by challis0124

I am not sure where this post belongs because I'm not sure exactly what the culprit is, so I'm hoping someone here can shed some light.

I am currently on an Island packet sailboat at anchor in an area with strong current and tide shift. I just noticed this evening there is a soft rhythmic knocking coming from somewhere on the boat...I can't pinpoint its location it sound like it's everywhere and nowhere. But it's continuous. Every few seconds it knocks 5 times then stops for a few seconds and starts up again.

I don't know if it's something on the deck( though I have checked all rigging and nothing that looks or sounds like this.) I live aboard my boat so am very attune to her sounds. I don't think it's anything on the engine, though I have heard prop shaft could cause something tho I'm not sure that's it either...maybe anchor chain ( though I doubt it). It almost reminds me of a woodpecker

Maybe a ghost

Any thoughts or if you have ever experienced this ? Much appreciated!

No ghost you pissed off Neptune.

Have you tried going around using a screwdriver as a stethoscope? My guess would be rigging but what do I know. Tracking a sound inside a barrel is a bitch. Good luck and let us know when you find it.

[topmast]

A hair caught in the valve of the domestic water pump, can let pressure drop and a bit of catchup.

[Cadence]

Originally Posted by topmast

A hair caught in the valve of the domestic water pump, can let pressure drop and a bit of catchup.

Damn good thought. I've heard that and it does sound like a woodpecker.

[Steve1944]

Originally Posted by challis0124

I am not sure where this post belongs because I'm not sure exactly what the culprit is, so I'm hoping someone here can shed some light.

I am currently on an Island packet sailboat at anchor in an area with strong current and tide shift. I just noticed this evening there is a soft rhythmic knocking coming from somewhere on the boat...I can't pinpoint its location it sound like it's everywhere and nowhere. But it's continuous. Every few seconds it knocks 5 times then stops for a few seconds and starts up again.

I don't know if it's something on the deck( though I have checked all rigging and nothing that looks or sounds like this.) I live aboard my boat so am very attune to her sounds. I don't think it's anything on the engine, though I have heard prop shaft could cause something tho I'm not sure that's it either...maybe anchor chain ( though I doubt it). It almost reminds me of a woodpecker

Maybe a ghost

Any thoughts or if you have ever experienced this ? Much appreciated!

Funny. I had the same thing and found it was my safety straps hanging on a hook in the house cabin. 😆😆😆

[jeepbluetj]

My boat does a very similar thing. It's the rudder on mine. Another cocktail or two solves the problem for the evening.....

[NirvanaBob]

Some thoughts:
1. Sliding closet doors that "flop" laterally in their track - ours does that when at anchor
2. If you use a "Y" configuration (meaning snubber that has two lines led through port and starboard hawse holes down to a single snubbing line on your anchor chain) anchor snubber, it may be that one "leg" is rubbing against the bow, and then a short period later the other "leg" rubs against the other side of the bow. Our boat has a dolphin striker and that is exactly what we experience when winds/tides/currents are not in alignment and the bow is caused to move laterally from port to starboard and back as it seeks alignment with those three competing forces.
3. Very slight rudder play as result of minor slack in steering cables between the helm and rudder steering quadrant.
Cheers and good luck running it to ground

[Cheechako]

Check your anchor roller, they slide from side to side knocking sometimes. It could be wear in your rudder shaft bearings too. Got fenders tied in a locker or along side? A bucket etc in a locker tipping back and forth?

[deblen]

Knocks 5 times,pauses & knocks 5 times.........

One of Santa's elves???


Merry Christmas!! / Len

[Cadence]

Originally Posted by Cadence

Damn good thought. I've heard that and it does sound like a woodpecker.

Quoting myself? The more I think about topmast's input and your description about the woodpecker. The more it makes sense. Periodic tap tap taps at intervals. For what it is worth?

[bumpman]

Don't know where you're located, but evening and woodpecker suggest that it could be the sounds of noisy fish (e.g. sea robins) reverberating through your hull. Many fish species do their evening calls just like songbirds. I've had these mysterious fish sounds both in NE and the Caribbean.