When it does this on my garmin unit it means it has lost the ability to track the bottom possibly due to turbulance you will probbably find when you slow down it goes back to normal...you may say it has been good since it was installed but mine started doing it at about 14 knots after being in the same location (the transducer)for about 5 years, no anomolies on the hull but culdnt correct it till I moved the transducer.

that sucks mine has been good for 18months

mine is doing it almost all the time it will settle for 5 mins then it goes again 

even at rest or speed its got its own mind 

did you move it lower or higher?

I tried it left right up and down from it's original position but it wasnt untill I moved it to the other side of the boat it came good again...check your hull in front of the transducer for the whole length of the boat for any chips etc or anything that could immpede the smooth flow of water over the transducer. like I said mine was perfect for 5 years I could track the bottom at nearly 30 knots then one day it just didn't want to play. also check it hasnt changed it's angle even a smidgen. try going at say 5 knots for a while and gradually increase the speed to see where it starts to play up and look over the back to see what the water looks like and if it changes when the unit reads correctly again....you'll need someone to drive though.

Check and see if the unit is in automatic or manual gain and range settings.  They work much better in manual settings. Good luck

ok after much playing today and readinfg 1000000 pages in the manuel worked out the sounder will work fine on 200hz

but will not work on 50hz it just flashes the depth that is what  ive always used the 50hz

is it possible that the trans ducer 50hz partt is broken?

or is it controled from the sounder?

you will need to check the sounder settings and see if the unit will send 50 hz ( deep water soundings ) if the unit works on 200 hz and not 50 the flashing is indicationg its nit reading the bottom signal, so you need to look at dual freq transducer setting ? and that the unit can simply change over to the other HZ , 200 hz should go up to 100 + mts before needing 50 hz

this was running fine on 50hz since new untill last week

i was told its better in water under 70mtrs after that then use 200hz

just dont understand why it suddenly stopped working???????????

try taking your sounder to All Boats in Kingsley and they should be able to test your sounder amd then you will know if its the sounder or transducer, you will probably find its a setting thats changed by accident

Try not to run your sounder with the transducer out of water. Apparently it damages it.