Resolution on fishfinders

[CTD]

I am planning on getting a fishfinder, I have narrowed it down to the furuno ls4100, Eagle fishmark 320 or Eagle fishmark 480. The Eagle 480 has 480x320 res, the ls4100 has 240x320 the 320 has 320x320. Is there a noticible difference in actual operation between 240,320, or 480 pixels. In theory I should be able to see a much more clear picture on the Eagle 480 than the Furuno 4100 but my last finder was a heathkit 60ft 60 fathom flasher so I am well out of touch with how these new things work. One last thing do shoot through the hull transducers preform as well as a transom mount.<br />Thanks for your opinions

 

[PAkev]

Re: Resolution on fishfinders

CTD,<br /><br />Resolution has a lot to do with the expectations of your electronics. Most quality fishfinders will identify fish and structure but higher resolution enables you to go above and beyond that. Such circumstances can be monitoring your rigs while trolling or discriminating between targeted species; Things competitive fishermen and guides often take seriously in order to maintain their success. Even then it takes some experience to understand the information the fishfinder is displaying. Higher resolution also comes with a considerablly higher price tag which the casual fisherman does not always justify. I personaly have a 240 X 320 display and am content with the resolution.<br /><br />Your two questions are directly related and as far as the transducer goes, anything impairing the sonar signal can diminish the resolution on your screen. Installation position of thru hull transducers and hull material are critical for satisfactory sonar performance. <br /><br />My .02 worth<br />Kevin

 

[Boatist]

Re: Resolution on fishfinders

CTD<br />In general if you use the unit in deep water then resolution becomes important. The vertical resolution is the only thing that really maters. The vertical affects what you can see. The horzional only affects how long before it scrolls off the screen. The Furuno LS4100 is a very good unit for deeper water and saltwater because in is a dual frequency. Also the dual frequency with the 50khz transducer very good if you use down riggers and want to see your downrigger ball. The 50khz transducer has a 45 degree cone angle. All the 200khz units usually 20 degrees or less. <br /><br />An example of what difference vertical resoultion makes. Your fishing 400 feet deep. With a vertical resolution of 320 like the Furuno and eagle 320. Fishing 400 feet or 4800 inches with a resolution of 320 means each pixel equals 15 inches. Normaly it takes two pixels to pop up before you will detect the mark. So fish would have to be 30 inches high before your would see it. With 4 times zoom fish would still need to be 7.5 inches high before you would detect it. With the 480 resolution fish would need to be 20 inches high before you would see it, with 4 times zoom fish would need to be 5 inches.<br /><br />Fishing 100 feet or 1200 inches with a 320 resultion fish would need to be 7.5 inches high before you are likely to see him. With 4 times zoom fish would need to be 1.875 inches high for you to see him. The 480 resolution at 100 feet fish would need to be 5 inches high to see it or with 4 times zoom 1.25 inches. <br /><br />At 50 feet 320 vertical fish must be 3.825 inches and with 4 times zoom .956 inches. The 480 vertical resolution 2.5 inches and .625 inches with 4 times zoom. <br /><br />So you can see if fish in less than 50 feet of water all will probably work ok with out zoom.<br /><br />With zoom you only see 1/4 of the water under the boat. In 100 feet and a 4 times zoom you will see water between 75 and 100 feet, so if your fishing for salmon and fish are in the 30 to 35 foot depth like normal you will never see the Salmon.<br /><br />I hope I have made this easy to understand.<br />I guess another way to say it is if plan to fish water under 50 feet then all the units you listed will work fine. In water over 50 feet I would buy the higher resolution.<br /> <br />I will add one more thing, before you buy take a look at a color unit. They cost a lot more and give you the same information but eaiser to veiw from any angle and I think worth the difference. They last a long time if you take good care of them and take them inside out of the sun and heat when not in use it will last a very long time. My 1981 unit looks and works like new. I also like Lowrance fish finders for water under 400 feet.

 

[CTD]

Re: Resolution on fishfinders

Thanks for the info guys. Boatist, I never thought about resolution that way, makes a lot of sense and I realise I neet to be sure one I get has zoom and selectable scanning areas. Is the first number height and the second number width on the screen? I think most trolling is done in under a hundred feet and most bottom fishing in less than 200 so I'll not put a lot of money into seeing down 500 ft or so. I used to fish for salmon out of Bodega 20 yrs ago and hope to get back out there next year. I've never looked at color ones, thought they were too expensive.

 

[ThomWV]

Re: Resolution on fishfinders

Well, actually what Boatist said is just slightly off, but not by much. Actually I'm pretty sure he just mis spoke, because I've seen him explain it before and the little thing I'll mention was right on the mark.<br /><br />Yes, divide the depth by the vertical resolution and you get the size of target that a pixel represents, but that doesn't mean that the smallest thing that can be detected and shown will have to be at least that size, not at all. What that means is the smallest size that can be displayed is equal to that mathmatical result. The fish finder can still accept returns from smaller objects, of they are strong engough, its just that it will only light up that single, or double, pixel to show it on the screen.<br /><br />Here, think about it for just a second. How does the fish finder know how big a target is? I'm not talking about how long the mark is shown on the screen, because that's just a matter of advance rate and how long a usable return was being echoed back from the target. No, what I mean to ask you is how does it know how thick a target is? It should occur to you pretty quickly that its the strength of the return and the rate of decay of the echo that do it and once that registers it quickly becomes clear that it is the strength of the return signal, not the actual size of the target that determines if a pixel is to be lit up or not. Of course its all dependent on the sensitivity of the transducer and the hard- and soft-ware in the fish finder display unit to both be able to discern noise from usable signal, particularly faint ones, and then to be able to segregate and amplify the returns to a point where they are suitable for the display unit. <br /><br />By the way, have you ever passed over a Tarpon in the boat and seen its signature on the fish finder screen? They light up the screen even brighter than a Rockfish, but curiously enough the fish always look sort of flat. I believe its because of the large scales that give a sharp return with an almost immediate decay of the echo so it appears there is no fuzziness under the fish.<br /><br />Anyway I just wanted to point that out. Just because your screen resolution restricts you to being able to show a target no smaller that 5 or 6 inches doesn't mean that a smaller target can't be detected and displayed, it can. Its just that it will be displaybed as if it were 6 or 7 inches, when in fact it might only be an inch or two.<br /><br />Thom

 

[Boatist]

Re: Resolution on fishfinders

CTD<br />I fish out of Bodega every year. Trolling for Salmon on overcast or foggy days unually will find Salmon at 35 feet or less. On bright sunny days can be down to 50 feet. Mouching normal is 20 to 60 feet.<br /><br />Rock fish out of Bodega bay can only fish to 120 feet or 20 fatoms for the last 2 years. Cordel banks is closed to rock fishing. Rock fish only open Aug, Sept, and Oct. Lingcod must be 30 inches. Three types of rockfish you can not keep at all. Many botom fish now have size limits. Last two year Fish and Game has wrote more tickets for illegal bottom fish than Salmon. We went first week of Rockfish this year and was shocked how many people have no idea of the rockfish regs. Even Rick on new Sea Angler talking with 3 other party boats while on the way to Fort Ross area trying to figure out the regulations. I think between the four of them all party boat Captain's they finally got it right except they did not know that this year the sub limits were eliminated.<br /><br /> http://www.dfg.ca.gov/mrd/bfregs2004.html#northcentral <br /><br />What Thomwv said has some merit but signal strength will determine if you turn on a pixel not how many you turn on. It really a timing thing as to which pixel you light up and it is true if you get a fish on the edge of the pixel time you can light up two pixels. A fish like a Salmon you can actually see the fishes cavity with a good unit. <br /><br />Vertical and Horizontal resolution can be listed in different orders. Click on the spec and it should tell you or look at the screen and the wider direction will be the higher number.<br /><br />I have not purchased a color unit either but next unit I get will be color weather it is a fish finder or gps. I had a chance to ride and see some of the color units and they are great. You can see the display from anywhere on the boat not just right in front of the unit. I really like some of the Lowrance units. Problem I have is my old 1981 unit works great. Also being an older unit has many more controls. When everyone went to the menu systems to make it simple for people who will not read the manual they did away with a lot of the features I loved. Anyway to me a color unit is worth the money but then that is just me. I have a Garmin Gps also that is hard to read in certain light condition like rideing in a car. Color unit eaiser to see. Also I expect any unit I buy to last me 25 years and over time I rather get a unit that is easy see and get information off of. <br /><br />Good luck in your search. When you find your unit make sure you check the internet for a better price (not Ebay) or rebates from the manufacture. Iboats has some good prices.

 

[ThomWV]

Re: Resolution on fishfinders

Boatist,<br /><br />This is off subject but I think it will be of interest to you, and others too.<br /><br />I have a Garmin 2006, the gray scale version, and a Garmin GPSMap-76 that I use as a backup. I use the 76 in the truck as well as in the boat. In the truck its up on the dash, next to the window pillar, held in place with two small velcro tabs. The 76 is a pretty good GPS but its visability leaves a bit to be desired at dawn and dusk and its backlighting leaves a lot to be desired. Last weekend I got a brief chance to use one of the new GPSMap-76C color units. I was really amazed by how much better the viewability of the color unit was. I put on my fishing glasses, polorized of course, and very very much to my surprise the screen's viewabiltiy got better. Both my wife and I agreed immediately that our current 76 was headed to E-Bay and that before our next fishing trip we'd have that color unit up at the helm.<br /><br />Oh, and you are doing the right thing going to color on the fish finder. I'm on my third color machine now (Furuno 582L) and it would be hard to go back to a gray-scale machine.<br /><br />Thom

 

[Boatist]

Re: Resolution on fishfinders

Thom<br />Thanks for your report. I agree 100 percent. I also have a Garmin GPSMAP 76 and looked at the GPSMAP 76CS less than two weeks ago. I liked the display but was a little disapointed that the actual display was a little smaller. I am glad that the 76C base unit still comes with a ok base map and navigation aids. I was suprized that the spec say battery last 30 hours when the MAP76 is only 16 hours. Even when I get a color unit I think I will keep the Map76. I use it as a backup now on the boat, hiking, in the car to give a advanced warning for next turn to Ski resort or turn off. also I use it when I go on a party boat or someone elses boat to record fishing spots and where we went. When I get a color unit on the boat I will probally put it in our survival bag with the raft, flares and waterproof handheld radio.<br /><br />I love Furuno. I still use my old LC90 Furuno Loran C. I just like the way you get info, Range and Bearing, time to go. I have looked at the 582L and the GP1850WDF. Great looking units but also like the Lowrance LCX-19C. The Lowrance I got to see out on a party boat. I was impressed how even from the back of the boat could still see the fish and depth reading.