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Thread: Structures

  1. #1

    Default Structures

    So the oft-repeated mantra is to find structures on nautical chart if you're looking for butts. I would love to know how you are doing this when soundings are usually hundreds of yards apart. E.g. at the compass rose area in KBay, it is flat bottom for miles. Are you really finding pinnacles using a chart??

  2. #2

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    Quote Originally Posted by HomerJack View Post
    So the oft-repeated mantra is to find structures on nautical chart if you're looking for butts. I would love to know how you are doing this when soundings are usually hundreds of yards apart. E.g. at the compass rose area in KBay, it is flat bottom for miles. Are you really finding pinnacles using a chart??
    Clearly, you did not purchase the optional and much sought after K Bay decoder ring...me neither...but I keep watching CL and Ebay. Seriously, though, I've wondered the same thing. Thanks for asking.

  3. #3
    Sponsor potbuilder's Avatar
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    ride around the area with your fishfinder on and look for any changes in depth, a tiny "gutter" can be quite a fish holder on flat bottom, learning which way the gutter runs takes some work, fish will pile up eyeballs to tails in a little depression. Same goes for a little "knuckle" sticking up.

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    Member Jack in Alaska's Avatar
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    I did that very thing yesterday off of Stariski Creek in the Cook Inlet. I found an unusual feature on the chart, criss-crossed it from several directions, picked the center and threw the hook in 70' of water.
    The 1st line down hooked up and it was great fishing for 4 rods through out the tide. Going back again tomorrow. It will probably suck this time but usually 2 trips to a hole and then it needs a rest.

  5. #5
    Premium Member kasilofchrisn's Avatar
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    If I study a chart carefully I often find structure or areas prone to it.
    Say a shallower depth surrounded by deeper areas or vice versa.
    Some charts also list the known bottom type in some areas. Sand,rock,etc.
    I usually pick a likely area and then cruise around once there to dial it in.
    If the fishing is lousy I head to another likely area I have picked out.
    Of course after several years I have several good spots marked that produce regularly.
    If you look carefully in well known areas you can often find good spots using your charts.
    "The closer I get to nature the farther I am from idiots"

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  6. #6

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    Quote Originally Posted by potbuilder View Post
    ride around the area with your fishfinder on and look for any changes in depth, a tiny "gutter" can be quite a fish holder on flat bottom, learning which way the gutter runs takes some work, fish will pile up eyeballs to tails in a little depression. Same goes for a little "knuckle" sticking up.


    Exactly. Though I don't have knowledge of Kbay's structure, it's pretty universal that the larger and flatter the area is, the less structure it takes to hold fish. Don't look for pinnicles where there aren't any...look for small rises, gutters, etc...fish use whats available.

  7. #7

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    Can't say if this will work worth a darn over there, but it works so well here I'll toss it in the mix.

    We've found another form of "structure" that's really productive on flat bottom. It's the point at which one bottom type transitions to another. You can see that by watching what's happening below the bottom line on your fathometer. Basically the more black below the line and the closer it gets up toward the bottom, the harder the bottom. With very little experience you can spot the differences between muck, sand, gravel and hard bottom. Probably don't even need to know that, if you at least watch for changes. Around here muck bottom is worth avoiding, but it's really worth finding the place where muck turns to sand or gravel. It's a guess without eyes on the bottom, but from what we see the halibut seem to move along those margins at various phases of the tide, kinda like highways. If the fish aren't there when you arrive, wait a bit.

  8. #8

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    Potbuilder nailed it. A good sounder is worth it's weight in gold, when looking for bottom structure. A chart will only get you so far, and even then you are fishing the same spots everybody else with a chart is. When fishing a new area, I'll spin around 10 or so times to get a read of what's going on with the bottom. I've spent lots of time cruising around on flats looking for structure that ain't on the chart. My furuno nav net reads bottom when I'm running offshore, and I'm always hitting "mark" when I hit a bump in a relatively flat area. Sometimes it'll be a few weeks before I get back to fish it, but i've found 95% of my structure that way. I like bumps, dips, benches, and plateaus.

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    Quote Originally Posted by 270ti View Post
    Potbuilder nailed it. A good sounder is worth it's weight in gold, when looking for bottom structure. A chart will only get you so far, and even then you are fishing the same spots everybody else with a chart is. When fishing a new area, I'll spin around 10 or so times to get a read of what's going on with the bottom. I've spent lots of time cruising around on flats looking for structure that ain't on the chart. My furuno nav net reads bottom when I'm running offshore, and I'm always hitting "mark" when I hit a bump in a relatively flat area. Sometimes it'll be a few weeks before I get back to fish it, but i've found 95% of my structure that way. I like bumps, dips, benches, and plateaus.
    Well the secret is out now !!

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  10. #10

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    Great info. At least now I have better idea what is meant by "structures". Just loaded the g2 bluechart software on my Garmin and it has ability to render 3d view of sea bottom. That should come in handy.

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    Member JR2's Avatar
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    A buddy was telling me that the 3d view from Garmin is like cheating. He claims he has been catching halibut in places that he would have never even tried to fish before because he did not know there was a decent place to fish from the regular charts. Wish my plotter had that feature, just a year or two to old.
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    Member Anythingalaska's Avatar
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    Quote Originally Posted by JR2 View Post
    A buddy was telling me that the 3d view from Garmin is like cheating. He claims he has been catching halibut in places that he would have never even tried to fish before because he did not know there was a decent place to fish from the regular charts. Wish my plotter had that feature, just a year or two to old.
    I have that feature on my Garmin, and I don't count it as cheating. If anything, I think the 'fishing chart' on my Garmin that shows topographic contour lines of the ocean floor to be much more helpful for fishing than the 3D underwater view. Although it is pretty neat.

  13. #13

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    Quote Originally Posted by JR2 View Post
    A buddy was telling me that the 3d view from Garmin is like cheating. He claims he has been catching halibut in places that he would have never even tried to fish before because he did not know there was a decent place to fish from the regular charts. Wish my plotter had that feature, just a year or two to old.
    Anyone have any idea how accurate the Garmin g2 bluechart is? How does Garmin know what the bottom contours are for a piece of water? Is it all just extrapolated from our standard nautical charts, or do they have another source of data? I'm considering buying the upgrade myself. Thanks!
    "Miss Mary"
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  14. #14

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    There's a mountain of "interpolation" in all of them. Heck, you go back to the original "smooth sheets" or survey maps used by USGS while doing the charting surveys, and there are gaps all over the place. Anything between their actual measure points is "interpolated." Someone, somewhere, or some computer program, in USGS sits down and makes best guesses about what's going on in between the measure points and draws a pretty little line for all of us to enjoy on their charts. Then the independent chart and GPS folks use them to put out their own charts, adding more pretty little lines and great colors.

    But the bottom line is no one has any info about the huge gaps between the original spots measured by USGS. Good thing is, I haven't found too many navigation hazards they've missed such as rocks not on the charts (at least until you get inside 30' of water). In my experience they're more likely to add submerged rocks where they aren't than to miss them. Got a couple of nasty looking wash rocks out in front of my house, according to the charts and GPS. Nada. Zip. The water is 30-40' right there. Got another spot where the chart "interpolates" a channel through some reefs. Oops. Missed it by about 150'. Creep through the actual channel following the deepest water with your sounder, and your GPS sezz you're hard aground 150' from the channel.

    Whole lot of SWAG involved in charts, as in "Scientific Wild Assed Guessing." The smooth sheets and USGS charts are a nice foundation for all the GPS and chart companies to use for adding pretty lines and colors, though.

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    Member tzieli22's Avatar
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    Quote Originally Posted by healerf18 View Post
    Anyone have any idea how accurate the Garmin g2 bluechart is? How does Garmin know what the bottom contours are for a piece of water? Is it all just extrapolated from our standard nautical charts, or do they have another source of data? I'm considering buying the upgrade myself. Thanks!
    As best as I can tell, my new Garmin 1040xs is pretty accurate. I wish it was giving me my 3d view based on current sonar but I believe it's based on the maps and data on hand.

    is it accurate? From what I can see, pretty darn close in my book. I've been going around Seward to check my marks to remark on my new sonar and it gives some great insight I didn't have before. And the DownVu/SideVu part is actually the best to use to find your spots.

    is it cheating? No way, I figure after all the money I've spent going blind and helping the local fuel barges etc I'm due.... If you want to see it in action, go to youtube and search my name, I show the DownVu/SideVu in action. For me, I really like the new technology...
    Last edited by tzieli22; 07-06-2014 at 09:41. Reason: Typo
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  16. #16

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    I know that about 5 years ago they did extensive cabling and survey in KBay and Inlet. Assuming that a lot of the new 3D imagery comes from that but who knows.

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    Member Jack in Alaska's Avatar
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    Quote Originally Posted by Jack in Alaska View Post
    I did that very thing yesterday off of Stariski Creek in the Cook Inlet. I found an unusual feature on the chart, criss-crossed it from several directions, picked the center and threw the hook in 70' of water.
    The 1st line down hooked up and it was great fishing for 4 rods through out the tide. Going back again tomorrow. It will probably suck this time but usually 2 trips to a hole and then it needs a rest.
    Went back again today. Same result. Had another load of halibut.

    I am liking that bottom type idea by looking at the 2nd line on the depth finder. Makes sense to me.

  18. #18
    Member joebut1985's Avatar
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    If you go to the navionics Web page you can turn on the sonar structure it is real helpful

  19. #19

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    This is great info guys. Thanks. BrownBear - just as I figgered, but like tzieli22 said, I'm finding that the SWAG lines are fairly accurate and quite helpful.
    "Miss Mary"
    Kingfisher 2725, twin Yamaha 150's

  20. #20
    Member Bullelkklr's Avatar
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    I can't seem to get an underwater 3d view with my garmin and the g2 chip. sounds like I better look at it more carefully. It is a 496S model - so a bit old, but still has the g2 chip.

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