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Looking for Fishfinder Info - help
Guys,
I need to increase my knowledge about fishfinders. Not looking for "sonar hits the fish results in a dot" but in detailed stuff, technical things, tips tricks and such .... Stuff like what objects cause what returns under which circumstances. I have a Garmin 240 Blue, also am looking for users of this unit. I couldnt find any really good info on the web, does anybody have any links or knows about literature? But maybe there isnt any more to it ;) Matt |
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"Matt Lang" wrote in message om... Guys, I need to increase my knowledge about fishfinders. Not looking for "sonar hits the fish results in a dot" but in detailed stuff, technical things, tips tricks and such .... Stuff like what objects cause what returns under which circumstances. I have a Garmin 240 Blue, also am looking for users of this unit. I couldnt find any really good info on the web, does anybody have any links or knows about literature? But maybe there isnt any more to it ;) Matt I have a Garmin, not sure what model, but it doesn't matter. Here's the deal: Fishfinders show you the fish you can't catch. It's like watching Saturday morning fishing shows that make you say "Awww...sonofabitch! He's fishing right where I was a week ago and I caught nothing!" Their cone of coverage is never enough to do any good. The only value of under-the-boat electronic stuff is simply to show you depth, and help you learn about the physical structure of the places you like to fish. From there, you go to books, or people who understand better than you the relationship between structure and fish habits. Period. There is no free lunch. I don't care WHAT Tom says. |
On Wed, 22 Sep 2004 23:52:45 GMT, "Doug Kanter"
wrote: "Matt Lang" wrote in message . com... Guys, I need to increase my knowledge about fishfinders. Not looking for "sonar hits the fish results in a dot" but in detailed stuff, technical things, tips tricks and such .... Stuff like what objects cause what returns under which circumstances. I have a Garmin 240 Blue, also am looking for users of this unit. I couldnt find any really good info on the web, does anybody have any links or knows about literature? But maybe there isnt any more to it ;) Matt I have a Garmin, not sure what model, but it doesn't matter. Here's the deal: Fishfinders show you the fish you can't catch. It's like watching Saturday morning fishing shows that make you say "Awww...sonofabitch! He's fishing right where I was a week ago and I caught nothing!" Their cone of coverage is never enough to do any good. The only value of under-the-boat electronic stuff is simply to show you depth, and help you learn about the physical structure of the places you like to fish. From there, you go to books, or people who understand better than you the relationship between structure and fish habits. Period. There is no free lunch. I don't care WHAT Tom says. But, but, but - that's what I say!!!! There Ain't No Such Thing As A Free Lunch.... ~~ mutter ~~ Actually, you pretty much hit the fastening device squarely on the flat surface provided for the use of a person with a hammer to drive said fastening device into the objects to be fastened. Usually, fish finders aren't set up correctly for the conditions, transducers are almost always incorrectly installed and in general you are looking at what was happening, not what is. Doug is absoutly correct - they help you find structure and read the characteristics of the bottom.. The rest is understanding the relationship to the bottom and structure to the family of fish you are targeting. Every once in a while, you can see other things, but that comes with practice. Later, Tom |
~~ mutter ~~
Actually, you pretty much hit the fastening device squarely on the flat surface provided for the use of a person with a hammer to drive said fastening device into the objects to be fastened. Usually, fish finders aren't set up correctly for the conditions, transducers are almost always incorrectly installed and in general you are looking at what was happening, not what is. Doug is absoutly correct - they help you find structure and read the characteristics of the bottom.. The rest is understanding the relationship to the bottom and structure to the family of fish you are targeting. Every once in a while, you can see other things, but that comes with practice. Later, Tom Well, I have the finder mostly to tell my things like waterdepth and water temp, not really to find fish. and also it just has this "cool" effect to see in the water and know what swims there.... I think the finder is useful for finding fish in regards that you can tell if there is no fish at all or if there is generally some where you are fishing... My questions are such as: - Does the transduce just have to touch the water with the its bottom or does it have to be submerged? - for the sonar part I need to know things like: - what makes the return big? is it object size or density? - what shape of object yields what kind of return? apparently fish is archs but thats rarely the case in real life it seems ... - I often have all sorts of returns and speckles and want to know what it is that creeps under my boat ;) Not so much to catch and eat it but just out of curiosity. I.e. on my last boat trip I had a relatively small blob in 750 feet depth in a lake ... it was pretty much round/square. I wonder what the heck is down there? Maybe it was just a glitch or noise... - What effect has frequencey on the echo and return. MY finder has 50 and 200 khz, why does certain frequencies get used and how does frequency correlate with echo angle? - 200khz being pretty fast how does boat speed change the return? - up to what speed is the finder useful for identifying objects in the water? - etc. etc. :) Matt |
"Matt Lang" wrote in message om... - Does the transduce just have to touch the water with the its bottom or does it have to be submerged? The transducer doesn't even have to be wet! It is possible to install the transducer by glueing it on the inside of the hull. Such a technique generally cuts down the effective range of the sounder, but it can sure make installation a lot easier. - for the sonar part I need to know things like: - what makes the return big? is it object size or density? The "ping" is not a laser sharp beam, it is more of a floodlight. The beam spreads as it goes down, and by the time it reaches the bottom it can be covering a fair amount of area. If the bottom is perfectly flat, smooth and hard the returning echo will be fairly consistant and sharp. If the bottom is jagged and rocky you will get early returns from the closest objects and later returns from the farther away objects. The type of bottom can also cause the return to get wide. hard rock will provide a clear, crisp return. The ping can penetrate soft mud and bounce off a harder layer underneath. A layer of grass growing on the bottom can also provide an early return. - what shape of object yields what kind of return? apparently fish is archs but thats rarely the case in real life it seems ... The depth sounder makes a guess that it is a fish when it gets an early weak return. A fish will only reflect a small amount of the energy, so the returning signal will be weak. If it occurs significantly before a strong return it makes the assumption that it was some sort of object suspended in the water. Since most things either float or sink, something half way in between should be a fish. The stronger the echo, the bigger the fish. - I often have all sorts of returns and speckles and want to know what it is that creeps under my boat ;) It isn't necessarialy a fish. It is possible to get a reflection off of a thermal layer in the water. The fishfinder can sometimes be fooled by noise or vibration coming from other sources, like the engine or turbulent water. - What effect has frequencey on the echo and return. MY finder has 50 and 200 khz, why does certain frequencies get used and how does frequency correlate with echo angle? A higher frequency is easier to focus and will have better resolution on depth. Unfortunately, the higher frequencies also get absorbed faster so they tend to not be as far reaching. - 200khz being pretty fast how does boat speed change the return? - up to what speed is the finder useful for identifying objects in the water? The ping frequency doesn't determine how fast the sound travels, that remains the same for all frequencies. You would have to be going pretty darn fast and have a very narrow beam to to move out of the beam width before the echo can come back, sound moves pretty darn fast, especially in water. What is more significant is the interference that the speed might cause. What really messes up a depthsounder is getting pockets of air in the path. If your boat "porpoises" and causes air to get trapped under the hull then the depthsounder will go nuts. Obviously, if the spot in the hull where the transducer is located comes out of the water you will have trouble. At certain speeds vibration from the engine, shaft or rudder can cause problems. If the transducer is mounted behind a thru hull, strut, or similar irregularity in the hull the eddy currents and possible cavitation can wreck havoc on the transducer. Rod |
On Fri, 24 Sep 2004 22:20:25 -0700, "rmcinnis"
wrote: "Matt Lang" wrote in message . com... ~~ snippage ~~ - I often have all sorts of returns and speckles and want to know what it is that creeps under my boat ;) It isn't necessarialy a fish. It is possible to get a reflection off of a thermal layer in the water. The fishfinder can sometimes be fooled by noise or vibration coming from other sources, like the engine or turbulent water. You can also get interference from other sonars in proximity to yours. I've seen that happen on lakes with heavy fishing pressure. - What effect has frequencey on the echo and return. MY finder has 50 and 200 khz, why does certain frequencies get used and how does frequency correlate with echo angle? A higher frequency is easier to focus and will have better resolution on depth. Unfortunately, the higher frequencies also get absorbed faster so they tend to not be as far reaching. - 200khz being pretty fast how does boat speed change the return? - up to what speed is the finder useful for identifying objects in the water? The ping frequency doesn't determine how fast the sound travels, that remains the same for all frequencies. You would have to be going pretty darn fast and have a very narrow beam to to move out of the beam width before the echo can come back, sound moves pretty darn fast, especially in water. What is more significant is the interference that the speed might cause. What really messes up a depthsounder is getting pockets of air in the path. If your boat "porpoises" and causes air to get trapped under the hull then the depthsounder will go nuts. Obviously, if the spot in the hull where the transducer is located comes out of the water you will have trouble. At certain speeds vibration from the engine, shaft or rudder can cause problems. If the transducer is mounted behind a thru hull, strut, or similar irregularity in the hull the eddy currents and possible cavitation can wreck havoc on the transducer. Nice post Rod. Although I defy you to desbribe putting a through hull transducer in the Ranger as easy. The only other "issue" I would include is water density and speed. As water density changes, the actual speed and quality of the echo can be affected. Some finders use an algorithym to deal with that - that's why there's a temp sensor on most of the newer models. On other models, there are additional algorithyms to adjust for SOG (meaning the Speed Over Bottom rather than Ground in this case). The newer digital finders can do all sorts of interesting tricks with signal processing where you can filter out noise, interference and such, but you really have to be knowledgable about sonar to make the translation from fishing guyese to technicalese. Once you get the hang of it, you would be amazed at what you can see on the bottom. I have a new Raymarine color finder that I just installed on the Ranger with all the new DSP goodies - it's pretty amazing, I'll tell you what. :) But again, interpretating the results is the real trick. Depending on where the transducer is mounted, you are looking pretty much back in time rather than current time - what was rather than what is. Once you get the hang of how your target species relates to what you see on the finder, then it all starts to come together. Good luck. Later, Tom |
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