false reading on depth finder

[ted]

This is my first experience with depth finders since I bought my boat about a year ago. I notice that I get a lot of false readings on my Hummingbird depth finder. I can be in deep water but the depth finder is reading 3-5 feet deep. It seems that the false reading is at the 15 ft range. As the finder moves on to 30, 60 and then 120 range the depths are accurate. The transducer is mounted thru hull in front of the keel. The bottom of the boat is clean and the finders setting is in feet not fathoms. Any ideas?thanks..Ted

 

[Tom Wootton]

Some possibilities

I couldn't tell from your post whether there is a hole in the hull or the transducer is glued to the inside and "shoots thru". If the latter, it's possible a bubble in the hull material (or the glue) is causing false readings. Turbulence can also cause false readings, especially near the bow; so can floating debris like weeds, etc. I often find a line on the viewfinder about halfway up when I'm in the river. The line vanishes in the Gulf. Couldn't figure it out until I went for a swim in the river one day; diving down with my mouth open, I discovered saltwater about five feet down. The freshwater on top, having a different density, shows up on the display as a distinct line. That's my story, and I'm stickin' to it ('til somebody shoots it down!)

 

[LaDonna Bubak - CatalinaOwners.com]

Stuff

Fish, seaweed, gunk can all cause blips. You can turn down the sensitivity of the FF - on the river, mine is set at -2 and I still get the occasional bleep. Just the things we have to deal with by owning modern technology!LaDonna