In most installations, the sonar won't be useful at speeds over about 7-ish knots (actual speed varies greatly depending on location of mount, surrounding structures etc). Bubbles, air gaps etc can all cause big problems in getting accurate readings. Once you are familiar with the overall topography of the area (either from chart reviews or from your GPS with installed charts), the sonar is generally not used for depth finding in deep water unless you are travelling slowly (as in trolling for example). That is, if you're sure the bottom is far below you, the sonar isn't needed unless you are looking for fish, at which time you must go fairly slow anyway.lupette":23by7cci said:
In addition, most sonars will only read to a certain depth which is limited by the power and frequency of the sonar. The hummingbird dx200 should read depths to about 600 feet but there are places in the sound that are deeper than that and I find that my sonar (also rated to 600ft) doesn't always read accurately when I am in water exceeding 480 feet. The usual symptoms of "loosing the bottom" on the sonar is that it tries to find the bottom (there's some computer algorithm searching for the bottom signal) and often puts out numbers that are meaningless - e.g. way too shallow.
Other things that can result in way too shallow readings -
Temperature inversions or strong temperature gradiants in the water
Weeds and other stuff in tide lines
big and thick schools of fish (this is a good thing - doesn't happen too often)
Seals/sea lions passing beneath the boat.
Finally also note that your sonar will pick up signals from adjacent sonars - this typically happens when boats are within 50 yds of each other. On my unit, the result of interference from another sonar, is something that looks like scattered small fish from top to bottom.
In general, the best way to get a feel for the conditions underwhich the sonar reads correctly is use it a slow speeds while following a contour or known depth (easily done with a GPS, accomplishable with a chart when the bottom contours closely follow the visible shoreline) - increase the speed until you know that the reading is incorrect, slow back down and see how long it takes to recover. Do this a few times and you'll know the speeds at which you can trust the sonar readings. Then go to increasingly deep water a few times and see at what depth the sonar goes nuts.
Finally, note that most sonars have a number of settings that influence the gain and sensitivity and most have "fully auto" modes and manual modes for some or all of the settings. On my sonar, the fully auto mode for depth range often jumps to an inappropriate range for the depth I am at and then the sonar reads incorrectly (usually the sonar jumps to a shallow range when I'm in deep water). I find I get more reliable readings by setting the range manually.
Roger on the SeaDNA
I also have a 16 ft. angler :roll: have the same thoughts as what to do with the anchor and the stuff that goes with it :? . Maybe some of the others here will remember where it is at :embarrased . My remeberer is not as good as it use to be :smileo .
