finding structure with a finder

[procraftmark]

posted 02-22-2003 11:02 AM <br />--------------------------------------------------------------------------------<br />This is something that i wondered about for a long time and there is little info on it.<br />when trying to define the area of submerged structure such as humps and creek channels when reading a locator the screen moves right to left and shows the terrain change ,like it rising up as in a hump ,but how do you know you are 90deg to the hump, isn't it possible you are just clipping the hump to your side a little ,my question is this how can you define the actual size and perimenter of the structure?<br /><br />thnx<br />mark

 

[roscoe]

Re: finding structure with a finder

The way I do it is to make multiple passes over the area, with some passes being perpendicular to the original direction. This way you get an idea on size . You might find it to be a long ridge, with a hole or a log pile on one end. Throwing out a few small bouy markers can help you to get a good idea of size and shape. Then store that away in your brain, or GPS for future use.

 

[JB]

Re: finding structure with a finder

You can probably get a Fishing Hotspots map for the lake. They will show you what structure is there and your sonar can confirm it.<br /><br />An alternate approach is to get a Garmin chartplotting GPS and the Mapsource Fishing Hotspots firmware for the lake you are fishing. <br /><br />Then you have double confirmation of where you are and what's down there.<br /><br />Good luck.

 

[procraftmark]

Re: finding structure with a finder

yea but without maps how can you tell that the hump you see is actuallyperpendicular to the direction you are going, it might be going up or down on your side <br /><br />thnx, <br />mark

 

[JB]

Re: finding structure with a finder

You don't. Looking down with sonar is like looking at the world through a tube. <br /><br />The only way you know whats outside your view is to move the tube, like Roscoe suggests.<br /><br />Good luck.

 

[Boatist]

Re: finding structure with a finder

Procraftmark<br />Several things you can do to find exact center of a rock pile or stump. First when you find the structure turn down your sensitivite, this helps to make cone angle less. Remenber that structure is just like a fish and will also arch, so if off to the side or in front or behind the distance to the object will be farther. So knowing this set your zoom to it highest setting and criss cross the object until you find the shallowest distant, at that point your transducer will be directly over object. Ofcourse this does not work with fish as they can and will move. Another thing you can do if you have a dual frequency unit is make sure you use the 200khz as it will have a much narrower cone angle. Like the Lowrance units 50 khz has a 37 degree cone angle while the 200khz has a 12 degree cone angle. Run it in split screen dual frequency mode and you will see target first on 50khz screen as you get more over it will show on the 200khz screen. If really want to get even closer can buy a 200khz tranducer with a 8 degree cone angle really anything you see will be right under tranducer.<br /><br />Finding a cut or hole is harder, best way we have found is to take the unit out of auto range mode and run in manual. Next set the depth to about 3 time the depth, Slow down you transmit speed or chart speed. Now turn the sensitivy way up until you see the second echo of the bottom. This will make channels or holes really stand out as it doubles the difference. Here you are not looking for the first bottom signal but the second. What you are seeing is signal sent down and bounce back up first bottom then signal travel up to water surface back down and back up, second echo. This is why you need to turn sensitivy way up so you can see second weak echo, also must slow down transmitt speed or chart speed way down to give signal time to make second trip before transmit again. also to see must not be in auto mode and must have set depth to at least 3 time normal depth. Now just look for deepest water, will show up good. Some low power unit this may not work except in shallow water. Hope this makes since. It works well.