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Boat Forum / Electronics / January 2004Questions on fish finder
Can anyone tell me how beneficial a "dual beam 24/60 would be vs. a single 24deg? Also, any opinion on the Hummingbird Matrix 17/20/25 finders? Thanks, LD ì Depends exactly what you use your sounder for. The narrower the cone the more detail you'll read of the bottom. If you are looking for "holes" to place cray pots etc then you need a narrow beam. On the other hand to look for fish maybe a wide beam will give you more info of what is "around" the boat & not just under it. Some of the wide ones will even let you know if the fish is on the right or left side. Therefore if you want both then get a "dual" beam one for sure. Imagine a flat bottom with a 100 ft deep hole in the middle of it that is 10 ft across. If a "ping" from your sounder won't fit "inside" the hole then you won't see it at all. The echo will return from the edge of the hole. Now if you have (say) a one degree cone & it fits inside, then you'll see it. A bit clearer? BruceM > Can anyone tell me how beneficial a "dual beam 24/60 would be vs. a single > 24deg? > Also, any opinion on the Hummingbird Matrix 17/20/25 finders? > Thanks, > LD > ì Good explanation - Could you explain why if I have a 240 Blue 200/50/dual, why I would use it on anything but dual - if this apparently gives the best of both worlds - or is there an advantage to one of the specific freq. thanks > Depends exactly what you use your sounder for. > The narrower the cone the more detail you'll read of the bottom. If you are [quoted text clipped - 16 lines] > > LD > > ì Do you want me to repeat all I wrote? 200 (ithink) is narrow for better bottom reading. 50 is wider & better for reading fish in area. Both together will not be much dif that 50 on it's own. On some sounders 50 will be limited in ability to go DEEP & read bottom. So in deep water using both (dual) might increase bottom echo. The main dif is your ability to use & read the sounder. For the few bucks more, I reckon you should maybe get it & learn how to get the maximum out of it. BruceM > Good explanation - > Could you explain why if I have a 240 Blue 200/50/dual, why I would use it [quoted text clipped - 27 lines] > > > LD > > > ì > Do you want me to repeat all I wrote? > 200 (ithink) is narrow for better bottom reading. [quoted text clipped - 6 lines] > the maximum out of it. > BruceM Actually your conclusions above are a bit missleading. 200 Khz will actually deliniate individual targets much better than 50Khz due to it's higher frequency and shorter wavelength. The Rule of Thumb for sonar is: The higher the frequency the better resolution of targets. The lower the frequency the deeper the signal can go. 200 Khz machines can't see down farther than 100 Fathoms in most cases, but can resolve individual fish easily. 50 Khz machines can see down to 1000 fathoms but can't resolve anything smaller than a cabin. North Pacific Crab fisherman use 28 Khz machines so as to get excellent bottom resolution at extreme depth, but they don't expect to actually see anything other than the profile of the bottom. Bruce in alaska  Signatureadd a <2> before @ Woops.......... knew I'd get it the wrong way. BruceM > > Do you want me to repeat all I wrote? > > 200 (ithink) is narrow for better bottom reading. [quoted text clipped - 24 lines] > -- > add a <2> before @ OK, I see the differences but I'm unlikely to need a finder to look deeper than 100' (in the Gulf of Mexico). Out of Pensacola, you have to go 15 to 20 miles out to get over 100' and I wouldn't do that very often in my 20' runabout. SO, is a dual beam, 24/60deg for example, needed or useful at these depths? thanks, LD > Woops.......... knew I'd get it the wrong way. > BruceM [quoted text clipped - 29 lines] > > -- > > add a <2> before @ > OK, I see the differences but I'm unlikely to need a finder to look deeper > than 100' (in the Gulf of Mexico). Out of Pensacola, you have to go 15 to > 20 miles out to get over 100' and I wouldn't do that very often in my 20' > runabout. SO, is a dual beam, 24/60deg for example, needed or useful at > these depths? > thanks, LD Ok, now we have enough information to expound on the question at hand. If you never expect to look below 100 Ft the a nice 200Khz sounder/fishfinder will work great in your application. 200Khz will give you excellent small target definition, and good target discrimination, if you use a very narrow tranducer like maybe 12 degrees or better. Most of the small sounder outfits don't spec the transducer's beamwidth, and just sell a generic transducer with an average 25 degree beamwidth. This will work ok for most applications , but will tend to not provide individual fish discrimination, that can be obtained with a narrower beamwidth. Power output for depths of less than 100 Ft at 200 Khz doesn't need to be more than 50 watts PEP. More will tend to fill the area with reverberations that just fog up the return signals, and reduce system clarity. Bruce in alaska Signatureadd a <2> before @ |
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