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Old 21-10-2006, 11:58   #1
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Depth sounder alarm in San Pedro Channel . . . ?

Several times when in the San Pedro Channel, to or from Catalina Island, my depth sounder has shown depth suddenly down to 30 feet.

This last time, the depth sounder alarm went off and the depth reading went down to 12 feet.

Never saw a dolphin, whale, or anything else in the vicinity and I do tend to look around continuously.

Anyone have any idea what I encountered?

Mary
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Old 21-10-2006, 12:07   #2
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Nope, but I too experienced that right off the LA breakwater channel before hitting the traffic lanes. Scared the heck out of me. Nothing on the chart. ::shrug::
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Old 21-10-2006, 12:10   #3
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was it a submarine?
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Old 21-10-2006, 12:17   #4
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Depending on the type and quality

of your sounder may be the cause. I've noticed with mine if I get into really silty waters, like at the mouth of a river in rainy season, my depth goes to 0 or will not show a bottom on the display. So then I have to make adjustments to it's sensitivity to get a proper reading again. Also a kelp bed may affect a reading if it's really dense.

My $.02........................................_/)
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Old 21-10-2006, 12:19   #5
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Pat - doubtful, most subs are out of San Diego Harbor. In addition, I think that the charted depth is about 50 feet .. too shallow for subs.
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Old 21-10-2006, 12:21   #6
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The other thing, though, is that there have been quite a few boat 'disappearances' that scuttlebutt has as having been scuttled just outside the breakwater.
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Old 21-10-2006, 12:23   #7
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D M - while that IS a possibility, I don't remember the visability of the water at the time. None of the local rivers would directly outflow to that area, but that doesn't mean the water wasn't silty.
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Old 21-10-2006, 13:01   #8
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In some situations, it is possible to get "ghost" echoes. Like a reflection of a the keel or a secondary bounce. This can be triggered by water layers, like differences in Salinity or even a fresh water layer, as well as water temperature layers. Bottom types can cause issues, but you don't normally see this untill you are getting very shallow. Dolphins and such are very hard to pick up, as the density is very similar to the water. Fish finders work by "seeing" the swim bladder in the fish, NOT the fish it'self.
Ensure you Transducer is clean, set the correct distance from Keel and the sounder is set to Auto Sensitivity.

I have a Friend that was an engineer on a ship and they had a Sub shadow them for three days aross the Pacific. They were in thousands of feet of water and the sounder showed 60ft or something like that all the way for three days. Then it went back to read the big depths again.
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Old 21-10-2006, 13:53   #9
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for a few years I thought that my depth sounder was playing up. Always around the entrance to Plimmerton it would only show 2 metres in 10 metres of water. I changed to a new Navman (but left in the old transducer) and it still happened. It would work fine everywhere else. Then I pulled out the boat and changed the transducer to the navman that came with the gauge. Still it happened. I just put it down to some strange thing in the area.
About 2 months ago it stopped happening and the depth sounder now reads correct.
Weird.
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Old 21-10-2006, 19:41   #10
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Out of all responses so far, a bounce off the top of a thermocline seems to be the most likely to me (if that's possible). It's the "30 feet" bit that gives me my hunch, and shallower is not unheard of. I sail SP channel all the time, but have never had this happen to me.

One thing for sure: it's not anything solid, but rather some kind of malfunction/dysfunction of the sounder.

But yeah, it would be, um, a bit unnerving to have my depth alarm, which is usu. set @ 15 feet, go off out there.
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Old 21-10-2006, 20:06   #11
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Mary,

Make mine another vote for thermal layers. The salinity idea has merit too, but only if there's a source of fresh (river or even a sewage outfall). Does the chart indicate pipelines or no anchoring?

Kevin
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Old 21-10-2006, 20:43   #12
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My passenger suggested a submarine

but I also doubt it. There would be no reason for one in the SP Channel, and besides 12! feet!

It usually happens in an area charted as hundreds of feet deep, and near an "unused" burial location. Hmm, so without going into gruesome detail the "silt" explanation seems reasonable.

Thanks for all your replies. That 12' reading and the alarm were startling, to put it politely.

Mary
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Old 21-10-2006, 20:51   #13
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Thermal layers, sometimes churned up by passing traffic (I've felt cold water welling up when a boat passed me 50 yards away in 25' of water), school of fish, loch ness monster...

Sounders do all that. The trick is to also have a chart around, and if you aren't sure of the depth you are in...check the chart. Odds are it is right and a blip on the sounder is just a blip. (You can drop depth charges to see if that clears it.<G>)
On the other hand, if it always shows the same shoal, or starts reading shallower and shallower...don't stop to read the chart!
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Old 25-10-2006, 09:16   #14
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Back in '92 we were sailing from Marina Del rey to Catalina. (Is this close?) We saw exactly what you decribed. Suddenly were in shallow water. Scared me so bad I still recall it 14 years later {chuckle} I think we were getting near the north end of catalina when it happend, we were heading to twin harbor.

-jim lee
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Old 28-10-2006, 23:05   #15
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Question on OS 31

I noticed your thread while doing a search on CL Offshore 31. I have just trucked one home to my shop for a restoration and would appreciate the opportunity to discuss the boat with a current owner of CL OS 31.

SMC
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