# Sounder Readins...two bottoms?



## Dan A (Aug 29, 2005)

Hi,

Wondering if anyone can tell me if this sounder screen looks correct, what would be causing the 2 lines, bottoms? is it normal.


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## Guest (Jan 14, 2007)

I cant tell if its in feet or metres but I'm thinking by that fish your in a bass dam, so I will say maybe it's a thermocline if it's in 35 feet ?? :wink:

Cheers, Allan


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## Dan A (Aug 29, 2005)

The reading is in metres, and is only 20 deg transducer as well, was fishing in a Freshwater river.

Dan


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## Guest (Jan 14, 2007)

OK I'm with Hi Yo then, try backing sensitivity off a bit.

Cheers, Allan


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## Dan A (Aug 29, 2005)

Funda said:


> OK I'm with Hi Yo then, try backing sensitivity off a bit.
> 
> Cheers, Allan


Ok thanks, will do that next time I get these results.

Dan


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## deano (Nov 26, 2006)

Hi Dan,

There is absolutely nothing wrong with the sounder - a second bottom is caused by the relay bounce of the sonar. A ping is sent from the transducer which bounces off the bottom and is received by the transducer again. The time taken for the return allows calculation of the depth.

On hard bottoms and/or shallow water, there is a lot of 'energy' left in the ping after its return to the surface, so the ping bounces off the bottom of the boat/yak/water surface and goes back to the bottom for a second time and bounces (off again) before returning to the transducer for a second reading. This second reading is the second bottom that you can see. You will notice that the second bottom is exactly twice the depth as the real bottom - this is because the distance for two round trips is exactly twice the original distance to the bottom.

Backing off the sensitivity will only reduce the amount of information you will see - that is not a good thing IMHO.

Try (if your sounder has this feature) to set the minimum and maximum depths to exclude the false bottom. Alternatively use the manual zoom.


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## Guest (Jan 14, 2007)

Deano that all makes a lot of sense, some great advise there.

I have a wide beam sounder (Lowrance trifinder 2) on my yak and occasionally get this double layer, I've usually just backed off the sensitivity a little but as you say you do lose a lot of definition.

Having looked at the pic again theres very little if any surface clutter (or is that the surface clutter, it's hard to tell not knowing the H'birds display) from sensitivity being too high so I guess that cant be the reason.

Cheers, Allan


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## Russ (Feb 24, 2006)

Some excellent information and advice there deano, I will put that in the memory bank, as I too have experienced this.

 fishing Russ


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