Topic: navigating a contour

[fishnfry]

What is the best way to follow a contour? I have a 998C and when I try to follow a contour I always seem to be up in shallow water before I see it on the screen. Any incite would be greatly appreciated!

[ITGEEK]

I guess, before you start following a contour, start off in deep water, and make
sure your boat icon on the map page matches where you are on the water.

On your map page, you will have to zoom in to follow the
contour precisely, then zoom out, so that you can see
the big picture.

If you zoom in too far and keep the map screen there, you won't be able to get
your bearings as to where the boat is in relation to the shoreline.

I guess as with anything, it will require practice.

[Gattlin]

  If I,m have a hard time with boat control I'll try and maneuver the boat INTO the wind, not with the wind. If you have the map card that you can change depth contours color,, change the target area to green and areas shallower than you intend to fish "Normally eight feet or less unless I,m casting for bass" to red also set the depth alarm to a couple feet shallower than you intent to fish. And Zoom Gps navigation to close not the closest setting but the next one up or there abouts.

Good Luck and good fishing:)

[sonar2000]

I am not sure of the accuracy of the map, due to lake changes or time since the map was made.
Or even depth changes if on a corps lake. Or tidal areas.

Chuck

[ITGEEK]

Also,
Are you getting the best out of your GPS accuracy?
Does your GPS receiver have a clear view of the sky.
The more satellites it can map, the more accurate your fix.

[Moose1am]

It depends on which lake maps you are using and from what company.  Also the contour lines can vary for each lake on some Companies Digital Lake Maps.

For example the Lake Master IN/OH version 1 map has 1 ft contours on two of the lakes I fish in Warrick County, IN but only 10 ft contour lines on Patoka Lake in IN. However the Monroe reservoir  up by Bloomington, IN has High Defination contour lines.

Accuracy of each map can vary depending on how the depth and position data was colllected and how it was processed. 

Some digital lake maps allow you to offset your position or to raise or lower lakes water levels.

Once you get the right map it may be a lot easier to follow a contour line.  For example with the new Lakemaster Maps you can high light a certain contour line and then make that line a different color so that it's easier to follow that depth contour line.  You can even as a plus or minus value to the contour to high light.  For example you can high light the 10 ft contour line in Green on a blue lake background and then also highlight the 11 ft and the 9 ft contour lines on each side of the 10 ft contour line. This makes the green part of the map wider and easier to follow.

And as mentioned in the other posts above the GPS accuracy and speed of the map update will help you follow the contour line better.  The accuracy of the GPS on these units can vary by plus or minu 3 meter even when WAAS is used.  So the more accurate your gps is the easier it is to see where your boat is on the map.

I've got the Navionics East Platinum Digital Map card and just got the Lakemaster IN/OH ver 1 digital Map card and I'm comparing the two digtal maps and the lakes on them.  I was pretty disappointed in the Lake Master Map of Patoka Lake. I was expecting that lake to be in high def but it's not.  That's a shame and really is a disappointment to me.

What is the best way to follow a contour? I have a 998C and when I try to follow a contour I always seem to be up in shallow water before I see it on the screen. Any incite would be greatly appreciated!

[Drifter]

F&F,

If you're asking about a contour on the navigation display, all I'd add to the above replies is to mark waypoint at the areas your tend to over shoot for future reference. If you're referring to physical contours and trying to follow them using the SI sonar display, it helps to have the transducer at the front of the boat. If it's mounted on a trolling motor (or a similar mount that can be rotated), you can turn it slightly to "peak ahead". Again, marking turns with waypoints will help for future use. In general I get a better reading of a contour on the SI display by "shooting" (running it) from the shallow side when I am "mapping it out" using the towfish.

Dog Leg ...


< click to enlarge >

Darrell

[fishnfry]

Thanks for the info . I think by marking way points along the contour may help. It just seem by the time I see the shallow water coming on the screen I am already up into it.

[Moose1am]

The new humminbird 360 will help you follow the contours easier as you can look out ahead of the boat and see what's out there before you get there.  Although it will cost 2 grand to do that.  Pretty expensive transducer.

[sonar2000]

Yes it is expensive especially since you can put a transducer on a trolling motor or a pole and at the front of the boat (if you turn it slightly sideways) it will look ahead for a short space..
I would suggest not to go very fast also..
Chuck

[Bob B]

Thanks for the info . I think by marking way points along the contour may help. It just seem by the time I see the shallow water coming on the screen I am already up into it.

Are you using your GPS and mapping to help determine where you are, or are you just watching the depth on your sonar?

[fishnfry]

I am just using the sonar. I'm trolling no more than 1.4mph

[rnvinc]

My primary crappie fishing method is, also following contours as crappie are very depth oriented...

Before SI.....my most advantageous tool for following a contour...was a contour map of the lake I fish.....(now I just study my maps on my 1197 chart view)....

This beforehand knowledge (of a hard copy topo map) is handy in that it allowed me to study the basic contour I wanted to target before I ever put my boat in the water....so before I even lauched, I knew basically where the creek channel should be and what direction it ran.....I knew where deep water was close to the bank...I knew where the open flats should be...

Whether it be early spring and following creek ledge contours...or spawning season following shoreline contours..it is important to know the basic direction the contour is traversing in relation to the other lake observations...(shoreline, points, bays, inlets, etc)

Get a good topo map of the lake you fish (or study the maps in the DF unit if it has maps) and study it for the lake bottom topography contour that you would expect your target species to be relating to at the time of year you are planning to fish......

Rickie

[Bob B]

I am just using the sonar. I'm trolling no more than 1.4mph

Why aren't you using your GPS to help you keep track of where you are?

[fishnfry]

I am using my GPS but by the time the screen updates I am already in shallow water

[Bob B]

Guess I'm confused.....in your previous post, you said you were just using the sonar to determine where you are on the breakline.

If you are using the GPS in split screen, you should be able to see where the boat is relative to the breakling before you get to it.

[fishnfry]

Thats what I am saying . By the time I am see my position on the screen and the depth. I have already came up into the shallow water

[fishnfry]

I guess I should say as I see it coming up I am already in the shallow water. It is a relatively steep contour but not a straight bluff

[Moose1am]

Fishing a ledge huh?  Those can be tough to fish as I know that the GPS screen doesn't update fast enough sometimes.  You can sometimes change the display settings on some gps units to make them update the screen faster.  Turning down the amount of information shown on the screen can do this. I do this with my Garmin eTrex Visa GPS handheld.  My Humminbird 898 screen updates faster as they used a faster processor in this unit. 
Are you using auto zoom or zoomed in really tight? 
Again I think that in a few more years when the prices of the new Humminbird 360 comes down and you and I can afford to buy one of these it will change the way we fish.  We can have more real time information on whats out in front of or to the side of the boat.  It's like a Radar for above water but it sees under the water all around us.    They just have to lower the price a lot and figure out a better way of making sure that the transducer doesn't get damaged when the boat starts to move or you go over some standing timber in the lake that's only 2 ft below the water's surface. That would tear the new 360 up pretty quickly. Perhaps an automatic retraction when the unit senses an object getting to close to the transducer.
Until then I'd use a series of waypoints to mark the ledge and then go to map view and use that to navigate the underwater ledge.  That's how I'm doing ledges right now.

[fishnfry]

I sure would be nice to have a 360 but I'm like you it's a little steep for me. Thanks for the info!

[Moose1am]

Why aren't you using your GPS to help you keep track of where you are?

One that that I noted (We all noted this some time ago) was that GPS is not that Accurate.  They claim it's plus or minu 10 meter or 3 meters.  That's about plus or minus ten feet.   If you are following a 10 ft contour and the next contour line is 0 ft or dry land you can easily end up on dry land when following the 10 ft contour line.   This is just the best we can do with the current GPS accuracy for the general public.   And if you are going very slow  the GPS/SI/Depth/map won't even see you are moving and can put your boat icon on the map anywhere within a 10 ft diameter circle.  That is just the inherent inaccuracy of the current GPS system.   

Satellites orbiting the earth send out very weak radio signals that are date/time stamped in the radio signal and are timed by the GPS receiver in order to calculate your position on earth.  The more different GPS satellites your GPS receiver gets signals from the more accurate your position is calculated and shown on the digital maps.  IE YOUR BOAT ICON shown on the map on the screen.

I'm constantly getting into shallow water when my map boat icon shows me still in 15 ft of water depth.   And the better the lake is surveyed the more accurate the contour map.   I learned to make contour maps when I was in College Physical Geology Class and we drew them by hand using simple data points of Depth & Position data.  Today these maps are drawn using a computer program such as AutoCAD or other similar programs.  Programs like AUTOCHART PRO do this as well.  But the program can only draw an accurate map if it has accurate data for each point in the grid along with the correct depth at that point on the map. 

If your data points are all only accurate to plus or minus ten ft. at best then you can see how the map might have some inaccuracies.  We see these inaccuracies when we try to follow the depth contours of our digital maps and run aground from time to time.  This happens to me more when the contour line is jagged and not straight. 

Which is why I recommended above to use the 360 devise so that you can actually see the bottom in real time and make corrections to your line of travel before you run into these shallow areas. Remember that shallow areas will show up as "lighter colored" area or Brighter areas on the screen's display.  If you go really slow you can actually see what's ahead of your boat and drive around the shallow areas and truly follow the actual contours on the lake bottom in real time. 

I wish that the GPS system were more accurate.  But atmospheric disturbances in the earth's space between the satellite and your position on the ground can vary and effect the accuracy of the signals.  The signals are weak remember and their timing varies as the atmosphere conditions change with time. 

Now there are very expensive surveying type GPS receivers and Military satellites signals (frequencies that are encropyted) that the military uses during war time and these are more accurate.  Plus or minus several inches or feet instead of tens of feed.  They would give us better accuracy if we could afford to buy them and were allowed to use these military satellite signals and receivers. 

Civil Engineers and Surveyors use very expensive GPS receivers that can average the GPS satellite signals over time and get more accuracy.  I'm not sure exactly how they do that but I've read that they can get accuracy in the centimeter ranges.

Remember that my grandfather used to use a rock tied to a long rope for his depth finders and they still caught plenty of fish back in the day.  They would love to have what we have today.