Have you got your gain too high for your depth or maybe your tranny position is wrong ( pic would be good ) .. auto settings is a default , you would have to switch it off to make manual settings I think . Usually would be a tranny alignment problem try adjusting it according to manual .Good luck , tranny's can be a headache setting up .

Either gain or may be getting turbulence (air bubbles) across the face of the transducer,  What hull and a pic of tanny position from behind would help.

The Transducer looks to be ok, installed the correct length away from motor, and vertical to the bottom of the boat (will get a pic though tonight) - i thought it was more the settings as when i manually adjusted the depth, the snow storm had stopped and looked to be working ok, moy original transducer (in the same spot) worked perfectly automatically.

i have a humminbird - where would the gain option be, im guessing i would need to reduce this?

thanks for the feedback gents

Mines Lowrance but at a guess gain may be named sensitivity.  You're probably right as if it was turbulance it adjustments would probably not alter it (or certianly not much anway).

no problems i will play around with the sensitivity settings, was a bit hard to adjust on saturday due to my Corona continuously getting in the way.

Thanks again.

And only look at the bottom 10 metres - this avoids any surface clutter

http://www.fishwrecked-reeltime.com/Gallery1/albums/userpics/10352/IMG_0001.jpg

thanks Scuba fish - gives me a good idea.

Is it a shoot through or transom mounted transducer (as per scubafish's link).  If through hull shooting through air bubbles in the resin used for the mount could still be a problem even though previous one was mounted in same posistion.  I thinking transom mounted (hanging off the back rather than in hull).. ...

Re-read your original post given its speed/movement related i'm back to thinking turbulence.  If picture is all right at rest shouldn't need to back off sensitivity when underway (at least until higher speeds when tranny is leaving the water).

Sorry for the questions but I've been down this path before with a few boats and now have them pretty sorted. 

Cheers

Paul

 thanks for asking the questions, its hanging of the back - looks like the boat has had one on the iside of the hull before, which one will give me the best reading?

could it just be the section of the river, seems to always go haywire around mayland, i really need to get it back out on the ocean again.

also i used to have a strong signal of blue and red for the bottom, now i have a weak light green signal.

i thin i should be apologising for all the questions, thanks again

Its almost always the tranny. Start there first. Depth, angle. Transom mount must angle slightly down at the back, critical to work at speed.

http://www.fishwrecked-reeltime.com/Gallery1/index.php?cat=10352 Three photos ,not shore if you saw all.

Thanks Scubafish for the info, i think i will keep the tranny on the back, just need to fiddle with the settings again to see if there is any issues again.

Im guessings its a bit of trial and error - good to know its not the system itself but more the position of the tranducer.

do your readings differ between ocean and river?