Humminbird 580 erratic depth problem

Zee, sorry to hear of the problems.

My Hummingbird sounder jumps around when I first launch in really shallow (1-2 ft) but settles down whether I turn it on before launch or not

My suggestions (how I troubleshoot these things by process of elimination):

1) drop the transducer over the side of the kayak to eliminate the mount issue (if it persists it might be the cable or the connection or the transducer)

2) if it works fine in #1, then it is the mount--either water leakage or mount corruption

3) Make sure you don't have a leak under the foam with the water draining out--had that once during a tourney first time I used a new foam mount--sonar was useless. If water is leaking out into the kayak, you got it nailed--the air pockets that creates will make the depth readings go haywire.

4) If the water is staying in, then it is a corrupted mount--probably air bubble in the glue. You want only dense material (far denser than water--glue, kayak HD-PE, etc.) between the "puck" and the bottom of the kayak. Air bubbles are major issues as they are a material far less dense than water. You might need to re-seat the foam.

Geek Alert! Proceed with caution
-------------------------------------
Sonar uses sound waves and uses the calculated speed of sound waves in a particular medium (water) to time their round trip and hence calculate the depth. If the medium is different in density to water ( the expected medium) then the timing is off since the waves travel faster or slower than expected and the constants in the formula are wrong. That is why, BTW, sonar units have an adjustment for salt versus fresh water--different densities--subtle but it's a percentage factor (linear equation constant multiplier) and the error increases linearly with the variable--the depth. But when the density change is radical (like air to water) some of the waves are reflected and refracted (like light is refracted at the air-water boundary distorting our sense of distance looking down in water at an angle). A little density difference between water an glue or kayak hull is no big deal but air is so different it makes a big difference--some of the waves reflect on the air-to-kayak boundary and some of the signal returns early and then the other signals (staying true to course) return much later--hence the bad and early readings. The sonar unit is confused and fooled. But maybe intermittently--hence the seeming "flakey" readings. Also, lube your contacts with a grease made to protect electrical contacts in water and particularly salt water--contact corrosion can add electrical resistance and therefore throw off timings (the electrical resistance of the length of transducer wire is part of the timing formula and variations cause problems whcih is why you are never supposed to cut or otherwise alter the length of the wire because it will throw off the readings). I bought a tube of contact grease at West Marine years ago--still plenty left--one tube is a nearly lifetime supply.

Damn, I am a geek aren't I? If the fish find out it's all over they'll just laugh me off the water--shhh- quiet everyone

I have the H-Bird 383....

On my last outing to Paradice is hit the skids, the depth started jumping all over the place.....total FUBAR.... I had my t-ducer glued to the hull a few months ago and everything was working fine. Now I got problems.

Thanks to everyone for the info and advice. I'm gonna check the ducer, then check the connections...then the air bubble glue down....Hopefully I get it worked out...

As for the F.F. Class, that sounds great.

Jack