Depthmeters
Moderator: Jim Walsh
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Guest
Depthmeters
How do depthmeters work? A sonar ping off the bottom? Does it matter if the boat is heeled over and the transducer is not aimed at the bottom?
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Tom
Re: Depthmeters
Basically that's correct. I don't know if you'd call it a "sonar" ping because you don't hear any sound like the guy with earphones in the submarine movies, but whales and dolphins are thought to hear it. When your transducer sends out a "ping" it isn't a straight beam but rather a fan shaped affair, thus the returning echo covers a wide area. This means that even though you are heeled over your transducer will pick up the return echo even if you're not pointed directly at the bottom.
One thing that does disturb it though is bubbles in the water. A passing boat with the engine running puts disturbance in the water and your depth sounder will sometimes "read" those bubbles or waves as the bottom, it will also "read" a school of fish passing under the boat. When you get in water that is too deep for your machine to reach the bottom, it will sometimes read its own ping as bottom, however these readings are usually erratic. 200 feet and then 2 feet a second apart and things like that. When you get within the depth range of your meter you will start getting steady depths that change very slowly. If a boat passes you with the engine running the turbulence can sometimes last for quite a long time maybe 30 seconds or so.
The depth meter is an electronic aid that one uses in conjunction with your other navigational aids. You know where you are on the chart and thus you know what depth you should be reading on the meter. If the chart and your readings don't agree that's a warning sign for you to check your position and use every aid that you have to resolve the disagreement. If you start getting a steady reading that smoothly starts going down 10 - 9 - 8 - 7 - 6 that probably means you are going aground very shortly. If you are out in the middle of the fairway and the bottom is reading 30 feet - 30 - 30 and then you suddenly get a reading of 4 feet you can usually look around and find the cause in a passing boat or figure that it is seaweed or fish etc. It's usually when you get a steady reading that is decreasing gradually that you have to watch out especially if you're on the edge of a shallow area. Heeling over will not usually affect the reading of your fathometer. Hope this helps.
TomCambria@mindspring.com
One thing that does disturb it though is bubbles in the water. A passing boat with the engine running puts disturbance in the water and your depth sounder will sometimes "read" those bubbles or waves as the bottom, it will also "read" a school of fish passing under the boat. When you get in water that is too deep for your machine to reach the bottom, it will sometimes read its own ping as bottom, however these readings are usually erratic. 200 feet and then 2 feet a second apart and things like that. When you get within the depth range of your meter you will start getting steady depths that change very slowly. If a boat passes you with the engine running the turbulence can sometimes last for quite a long time maybe 30 seconds or so.
The depth meter is an electronic aid that one uses in conjunction with your other navigational aids. You know where you are on the chart and thus you know what depth you should be reading on the meter. If the chart and your readings don't agree that's a warning sign for you to check your position and use every aid that you have to resolve the disagreement. If you start getting a steady reading that smoothly starts going down 10 - 9 - 8 - 7 - 6 that probably means you are going aground very shortly. If you are out in the middle of the fairway and the bottom is reading 30 feet - 30 - 30 and then you suddenly get a reading of 4 feet you can usually look around and find the cause in a passing boat or figure that it is seaweed or fish etc. It's usually when you get a steady reading that is decreasing gradually that you have to watch out especially if you're on the edge of a shallow area. Heeling over will not usually affect the reading of your fathometer. Hope this helps.
wrote: How do depthmeters work? A sonar ping off the bottom? Does it matter if the boat is heeled over and the transducer is not aimed at the bottom?
TomCambria@mindspring.com