My depth sounder LIES!

[BigJohn]

do you think it may be the peculiar location of the transducer?

[trooper dan]

Originally Posted by BigJohn

do you think it may be the peculiar location of the transducer?

The transducer is located about 1' before the keel, and at the lowest part of the hull.

[BigJohn]

Originally Posted by trooper dan

The transducer is located about 1' before the keel, and at the lowest part of the hull.

then perhaps you need to contact the manufacturer as suggested by others here ... an error of over 6' is downright dangerous ...

[Rakuflames]

Originally Posted by trooper dan

So I have a uniden depth sounder that is relatively new but purchased with the boat. I have run aground three times already and every single time the depth sounder lies about how much water I have under me. Today I ran aground and while I was stuck the sounder read 6'2" and my boat draws 3'8" so I should be ok right? Each time some kind power boaters towed me off. I am here on the Magothy river Chesapeake and on the northern end. There are very shallow water in the creeks and rivers here.

I have new charts and gps, and follow them closely. So anyways I used a lead line a little bit ago here at my slip and supposedly my boat is in 5'1" of water and clearly not aground. Indeed the lead line indicated 5' of water, So why would my sounder read 6'2" when firmly aground? It stayed at 6'2" the entire time i was aground until I got towed off. I cannot adjust this model of sounder to account for say "0" to be the bottom of my keel or I would. So even in these skinny waters here, what can I do?

I fell really silly getting grounded all of the time, what gives?

TD

Check the transducer compartment to make sure the fluid it's supposed to float in is still there.

If that isn't the problem, check the website for the manufacturer. You might need a software update. Easy to do, unless you have a Macintosh, in which case you may need a friend with a PC to download the software update to a thumb drive.

[Rakuflames]

Originally Posted by trooper dan

Oh yeah the thing is I never ask for help. I would be just as comfortable waiting for the tide to come back in. People are really nice and helpful around here! People just motor over and ask how I am doing... A catamaran looks really sweet right now! What surprised me the most was how firmly I was aground at such a slow speed. This guy today with a 125 HP outboard had a difficult time getting me un-stuck. Thanks goodness for the kindness of others.

I call some of the bottom here, a black muck, "God's superglue!"

[Rakuflames]

Originally Posted by Paul Elliott

How do you do that, given the huge difference in sound propagation speed of air vs water? Is there some technique? I suppose you could calibrate using a 0.231 scale factor...

Make a depth line. I weighted mine down with a round zinc.

I used 1/4" line and put one knot in it for every foot, with two knots every 3 feet. Then you hang it over the said where your transducer is, and compare the reading on the depth sounder to what the line says.

[Celestialsailor]

Two things which come to mind is 1) If the bottom is silty muck it may not give a proper bounce. Also, 2) there is a keel offset that you may not have set right.

[Sailmonkey]

Originally Posted by trooper dan

I was not under sail at the time, nor under heel. My depth sounder is malfunctioning, I think.

Under power in shallow water with a soft bottom this is a normal behavior for low powered sounders. The transducer is not powerful enough nor sensitive enough to combat all of the noise (engine, etc) and diminished return from a soft bottom.
Unfortunately if you want an accurate depth in these conditions you'll need something other than the inexpensive uniden depth gauge

[zeehag]

i use 2 sounders--one forward, set inside boat, is a grmin, with a liquid so it can read thru the hull. is correct.
i also have an apelco which has begun to malfunction-- i will be replacing both as soon as i can find a garmin with a good lens--mine went black. functioning well, screen blac, so i am getting a replacement
my apelco has begun to misread--when garmin says 9 ft, the apelco says 69 ft...lol...i will be replacing my apelco with, i hope, a comp[atible apelco that actually works. is good to have spares. i dont have em yet, but they are necessary. stuff happens.

also, make sure depth is under keel not water line, and not from transducer to bottom.. makes a difference.

[Kettlewell]

Get a small fishfinder--I have found them to be much more accurate and powerful than sailboat depth sounders, and they are cheaper. The bottom contour image is very useful too.