Mystery Noise

Last week we were on the hook 3 nights and in marinas the rest.* When we were on the hook we would sometimes hear a strange vibration that was literally loud enough to keep you awake all night (one night it nearly did).* The sound seemed to emanate from the transom area but from the bottom of the boat, and was very loud at times.* Like a fast jackhammer in period and the tone never changed.* The strange thing about the sound is that it is loud aft and isn't heard forward.

I looked everywhere and could not identify any stays, rubbing furniture, canvass, vibrating pumps or anything else and could never put my hand or ear directly on the source of the noise.** What I did notice is that the noise seemed to correspond to the speed of the current -- never noticed it during a slack tide.* At first I thought maybe one of my rudders was loose and somehow was being acted upon by the current since our boat was being pushed against it by a string perpindicular wind.

But my final theory is this:* I use a 25' snubber which was pulled tight like a guitar string down into the water.* The force of the current caused it to vibrate like a guitar string and somehow the tone resonated from the bow hawse pipe back through the boat and wasn't "released" until it hit the transom.* That is the only way I can think of where the sound is audible in the aft cabin and not in the forward cabin.** I was going to shorten or remove the snub to see if the sound went away but didn't want to do that in the dark at 1AM.

Ideas?* My theory might sound strange but I've heard some bridle chafing that was truly unbearable when on a mooring ball, so I know vibrations can travel in strange ways throughout a boat's hull.

The Flying Dutchman.

Just playing you a song.

ooo* eeee* oooo!!!
Sorry I couldn't resist** Halloween is near.

SD

-- Edited by skipperdude on Monday 11th of October 2010 01:09:05 PM

I wonder if you have the Monk 36 boat whos previous owner died while sanding the transom down preparing it for paint. I'd call Taps. Might want to do some EVP work.

Truth be known, the Monk design was stolen from a So Cal tuna fisherman/designer. The*original designer, now deceased,*is rumored to h(a)unting all remaining hulls.

sunchaser wrote:

Truth be known, the Monk design was stolen from a So Cal tuna fisherman/designer. The*original designer, now deceased,*is rumored to h(a)unting all remaining hulls.

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So I gotta go tell my wife that our boat is haunted by the ghost of Edwin Monk, and he's pissed because someone is putting his name on someone else's design?* I think our ghost doesn't like to be on anchor --*maybe I'll pay out a tad more scope next time just to be safe.

*

I read somewhere else (I think on the AGLCA forum) reports of bottom noise which turned out to be feeding fish of some kind hitting the bottom for food (barnicles, etc.). But I like the ghost theory too...

Another possibility is with abit of current flow can cause some props to "sing". However, I like my original theory better.

Dave

Actually, it's all about SEX!!* You may be hearing the "Singing Toad Fish"* True story.* Years ago they kept the whole harbor in Sausalito awake for about a month.* Made all the papers.* Biologists finally discovered the cause of the mechanical like noise and predicted correctly that once mating season was over the noise would stop.* Here's the story* http://articles.sfgate.com/2003-12-18/news/17522481_1_toadfish-myopathy-muscles.......................Arctic Traveller

charles wrote:

Woody,
In my case I was anchored on several different rivers in the current and it was so strong that it actually turned the wheels on the boat. To stop them I put a large pipe wrench on the shafts. It is surprising just how much noise the running gear actually makes. A roar!!!
CCC

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I thought the same thing so I put them in gear thinking that would stop the noise.* Do you think one of the props would spin even though I put them in forward?* Also turned the wheel hard over hoping that would help somehow.* Believe me I dang near tried everything and had it not started happening in the middle of the night I would have got down in the bilge with a flashlight.* Next time I will and check to see if the shaft(s) are turning.* Where I was parked could have been three knot current, best guess, possibly more.*

Thanks for all the creative ideas...

*


-- Edited by Egregious on Monday 11th of October 2010 07:34:14 PM

Woody,
The props would spin in gear. They only "lock up" when the charge pump is spinning and pressure can be applied to the clutch pack piston.

Egregious, I think your own theory re the snubber humming is still probably the most likely explanation. I can't imagine a 3 kn current being able to turn your props. Why not try just shortening the snubber so it's not actually under the water, and I would put money on it, the noise would stop - if it happens again. Chances are the coming together of the exact same conditions that caused it will not happen again however, just to tee you off....and leave you wondering - like was it really old Monks ghost...or whatever....he he he...