Instrument to record bottom depth

[skylark]

I need to find something relatively inexpensive that will make a record of the depth of the bottom.  My first thought is a fish finder and a video camera.  I need an easy way to check out the bottom of a river to see if any dredging is needed.  Quite often there are new sandbars after storms and the sooner I can find them, the sooner we can get a dredge in there.

It would be nice to have a record of bottom depth as well.

Anybody have any recommendations?

[Auspicious]

I've got a similar, actually more advanced, application.

One of the fish finders (I forget which one) will record a track with depths. It didn't work for me because I couldn't get the data out of the fishfinder electronically. For what you describe it might work for you.

I think it's Lowrance.

[Amgine]

Depth sounder with NMEA data out, but this won't do you any good without also having a GPS with data out.

The software I'm using, MacENC, can accept both GPS and instrument data, and will record all this data in its 'track', so you can see where the depth was when (allowing you to also adjust for tides.) Unfortunately, my depth sounder is too old to have NMEA output so I can't currently use this feature. But I'm sure there are a number of different plotter softwares which can do this for you.

It's not the cheapest solution - requiring at least a depth sounder, a gps, and a laptop - but it's a lot cheaper than the expensive charting hardware which need a super computer to interpret the data stream.

[newt]

I have a Garmin chartplotter/fishfinder/depth finder combo, but every once in a while I will go from 90 feet to 3 feet. I can't figure out why- water temp inversion? Being followed by a large mammal underneath? It just happens every once in a while but is very unnerving.

[s/v Faith]

I have a Garmin chartplotter/fishfinder/depth finder combo, but every once in a while I will go from 90 feet to 3 feet. I can't figure out why- water temp inversion? Being followed by a large mammal underneath? It just happens every once in a while but is very unnerving.

Which one do you have?

  Faith has a Uniden q200 sounder (same one you see on many sailboats).  The problem is the same though.  I have seen it on many sailboats.  Most every fish finder, flasher, and depth sounder works the same way.  Sound is generated by the transducer (usually at 50khz or 200khz) and then the reflected sound is analyzed and the delay between the transmission and reply are evaluated and a depth is calculated.  Most brands use the same transducers (Airex makes most of them, regard less of brand).

  If every signal was evaluated, you would get a value that would change faster then it could be displayed.  The device uses a 'filter' to display only the 'best' answer.

   In turbulent waters, when there are air bubbles from a long-passed boat... etc.  The 'best' answer is often the echo that reflects off of the edge of the keel... so you will see some low reading like the distance from your transducer to the tip of your keel....

  Can freak you out if you are in deep enough water, and suddenly see the 'aground' depth displayed.... you can play with your 'sensitivity' setting to get some improvement but that only helps so much.

[Captain Smollett]

I have a Garmin chartplotter/fishfinder/depth finder combo, but every once in a while I will go from 90 feet to 3 feet. I can't figure out why- water temp inversion? Being followed by a large mammal underneath? It just happens every once in a while but is very unnerving.

I was testing a transducer a few months ago by holding it just under the surface on a stick.  The readings bounced around like that, say from 3ft to 24 ft or so.  I thought it was bad, as I knew I was in about 10 ft of water.

Until I realized I had it mounted on the stick at a 90 degree angle (  ::) ), so that I was getting a reading off either the hull or the dock in front of the boat (in the slip).

24 ft was just about right for that distance to the dock.   ;D

[skylark]

I called Lowrance and they recommended this model, it will record a sonar track of depth and you can save it on to a removable SD card, which you can then put in the computer and view it or export it to a spreadsheet, which then can be imported into GIS software. 


http://www.lowrance.com/en/Products/Marine/HDS-High-Definition-System/HDS-5m-Multifunction-GPS-Chartplotter/