Had an unusual (well a first for me) a week or so back at the mouth of Pax River. Sailing in what appeared on both the chart and chartplotter to be an open, fairly deep stretch in the center of the river (avg depth ~50-60'), all of a sudden my wife pointed to the sounder-- "9'...7'...8'..." As I was personally sucking air from my own sails to slow the boat for what I thought was a sure bounce, all of a sudden we're back in the 40's...50's...etc. Whole thing took maybe 30-45 seconds. Didn't have the presence of mind to tag the coords at the moment...no wrecks, etc. in the area we were at. The rapid change in depth seemed a bit extreme for shoaling... Any thoughts? Similar experiences? Fish? Thx, Bill
What did I sail over?
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school of fish
remember its spring, the rocks and other large fish are migrating up the bay to spawn. you just sailed over a large school. happens all the time. capnjim sv "Que Pasa"
remember its spring, the rocks and other large fish are migrating up the bay to spawn. you just sailed over a large school. happens all the time. capnjim sv "Que Pasa"
depth finders
I've had similar experiences with depth finders out on the chester river. cruising along watching the depth finder it would jump from 28ft to 3ft and back again. Maybe its silt reflecting back? I am not sure. Unfortunately, if you get used to not trusting your depth finder, when it is accurate, you'll end up stuck somewhere...
I've had similar experiences with depth finders out on the chester river. cruising along watching the depth finder it would jump from 28ft to 3ft and back again. Maybe its silt reflecting back? I am not sure. Unfortunately, if you get used to not trusting your depth finder, when it is accurate, you'll end up stuck somewhere...
another possibility !!!!
If you have a data marine depth sounder and this happens a lot then the shallow gain may need a slight adj. I have to adj mine ocassionally. when it needs adjusting you will get consistant missed and very shallow readings even though you are in deep water. it will keep jumping to very shallow readings.
If you have a data marine depth sounder and this happens a lot then the shallow gain may need a slight adj. I have to adj mine ocassionally. when it needs adjusting you will get consistant missed and very shallow readings even though you are in deep water. it will keep jumping to very shallow readings.
Everybody-What about readings too deep?
My depth sounder has read 425' on the ICW. Then again it has read 0' in 8'of water. I don't feel like I can rely on it. Any more thoughts? Thanks! Mike
My depth sounder has read 425' on the ICW. Then again it has read 0' in 8'of water. I don't feel like I can rely on it. Any more thoughts? Thanks! Mike
A Tunnel
There is an access tunnel between the liquified gas platform above Cove Point and the shore. I sailed over it once years ago and almost fainted when the depth sounder did the same thing. It was a bright sunny day and you could see the tunnel through the water. I thought I was going to hit it. The depth above it was uncharted at the time.
There is an access tunnel between the liquified gas platform above Cove Point and the shore. I sailed over it once years ago and almost fainted when the depth sounder did the same thing. It was a bright sunny day and you could see the tunnel through the water. I thought I was going to hit it. The depth above it was uncharted at the time.
salt water intrusion?
I have seen anomalous depth readings on my standard horizon depth meter many times in situations like at a river mouth where a tongue of salt water may intrude up river in a wedge beneath the surface. Evidently the change in density is enough to fool the meter into thinking the saltwater interface is the bottom. Such an interpretation is probably instrument specific, but for mine, when it reads bogus, that's the first thing I look for.
I have seen anomalous depth readings on my standard horizon depth meter many times in situations like at a river mouth where a tongue of salt water may intrude up river in a wedge beneath the surface. Evidently the change in density is enough to fool the meter into thinking the saltwater interface is the bottom. Such an interpretation is probably instrument specific, but for mine, when it reads bogus, that's the first thing I look for.
Odd Readings
While sailing in the Catalina Channel in water that I knew was well over 300 fathoms, my depth meter would occasionally read 125' to maybe 200'. I asked around and found out it was probably thermal layers (inversion layers?). With nothing solid to send back a signal the colder water (more dense?) would return enough of a signal to register on my depth meter. Autohelm w/thru hull transponder.
While sailing in the Catalina Channel in water that I knew was well over 300 fathoms, my depth meter would occasionally read 125' to maybe 200'. I asked around and found out it was probably thermal layers (inversion layers?). With nothing solid to send back a signal the colder water (more dense?) would return enough of a signal to register on my depth meter. Autohelm w/thru hull transponder.
I agree with Mike
Thermal layers can bounce a signal that is interpreted by the depth sounder as ground. The three times I have sailed across the Gulf Stream I have had a similar experience. The first time it happened I was in panic because it coincided with the formation of steep breaking waves that form when the current runs in opposite direction to the wind. I kept looking at the charts and questioning my GPS position over and over until the phenomena stoped.
Thermal layers can bounce a signal that is interpreted by the depth sounder as ground. The three times I have sailed across the Gulf Stream I have had a similar experience. The first time it happened I was in panic because it coincided with the formation of steep breaking waves that form when the current runs in opposite direction to the wind. I kept looking at the charts and questioning my GPS position over and over until the phenomena stoped.
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