Funky depth return-Garmin 740S

localboy · Posted: Fri Jul 05, 2013 8:59 pm Post subject: Funky depth return-Garmin 740S

On the way back from Poulsbo I noticed the depth readout on our Garmin 740S flashing 95.3 feet. Weird since I was in about 500-600 feet of water. Powered the unit down and restarted. Now the depth showed no return; Nothing. Blank lines. After a few minutes it started returning 73.5 feet? WTH? Confused

I was in over 250 feet of water. Funky reading lasted 10-15 minutes. Then, suddenly as it all started..it began reading accurately. Confused

hardee · Posted: Fri Jul 05, 2013 9:47 pm Post subject:

HI Mark,

Sorry I can't speak directly about Garmin, but there are a lot of things that will affect your depth readout. Water surface, like little ripples can get air under the hull and have them (air bubbles) crossing under the transponder causing it to loose bottom lock. Any kind of seaweed caught where it will move under the t-ducer too, will have an effect. I have also noticed that sometimes crossing a tide line will cause bottom loss for a bit. I think that might have to do with temperature change. Also, if my stbd trim tab is all the way down and I make a medium to hard turn to stbd that I will loose depth readings for a bit. Once in really deep water (1500ft plus) it would not hold the bottom either, but with some sensitivity adjustment we were able to get that back. Now I usually run depth on auto to avoid that little glitch.

Is this a first time thing for you? Anything about conditions that may apply?

Harvey
SleepyC Moon

T.R. Bauer · Posted: Fri Jul 05, 2013 10:39 pm Post subject:

I have one too and on occasion it does basically what you described. I have found mine to be fouled with kelp, or is because the seas really suck and there's cavitation of some kind. I have also found they like full voltage (and do goofy stuff when they don't have it) to really work correctly when drifting around. It hasn't done it yet without some logical reason for doing it. Are you certain your wasn't fouled somehow?

DuckDogTitus · Posted: Fri Jul 05, 2013 10:49 pm Post subject:

I dont have that particular model, but I have experienced the same issue a number of times. It seems to only be in the salt or in areas of a lake which seem to have more grass growing below.

The other thing I notice it it very often shows fish at exactly the same location as my downrigger ball. Rolling Eyes

Larry Patrick · Posted: Sat Jul 06, 2013 7:43 am Post subject:

I had this happen several times in 150ft of water then reading 28ft, looked at chart and realized still in deep water,changed screens a few times and it fixed itself.

colobear · Posted: Sat Jul 06, 2013 11:20 am Post subject:

We have had the same thing on our Raymarine system. Went to the Fishfinder menu and played with the dual frequency scan (50 or 200), that usually fixed it. Seems to be just a fact of life for these small inexpensive systems.

starcrafttom · Posted: Sat Jul 06, 2013 2:26 pm Post subject:

large school of pinks ???

localboy · Posted: Sun Jul 07, 2013 9:34 am Post subject:

Wasn't fouled and I stopped and drifted in neutral to see if it would correct; it didn't. Oh, well. Barry's probably correct. It's not the end of the world and it seemed to work fine again on it's own.

dave · Posted: Wed Jul 10, 2013 1:46 pm Post subject:

Mine goes haywire sometimes, too. Sometimes for no reason. If I stop the boat, it will usually reset. Other times it is seaweed that I have to remove.

C-Dawg · Posted: Wed Jul 10, 2013 1:53 pm Post subject:

Might have been an uncharted pinnacle. Shoulda stopped and dropped a couple jigs to pick up some sea bass or lings. Very Happy

redbaronace · Posted: Wed Jul 10, 2013 3:11 pm Post subject:

We have the same unit. Ours does the same thing somewhat regularly and it drives me nuts. Overall given that my unit was purchased used, I have no way of knowing how a new one would be different. Our transducer P66 was new.

Overall, not very impressed with the unit, but an upgrade to more $$$ gear was not an option at the time.

For whatever reason, it just comes and goes. If you discover a solution to the problem, please post it. I will do the same.

dave · Posted: Fri Jul 12, 2013 12:40 am Post subject:

DuckDogTitus · Posted: Tue Jul 23, 2013 12:01 am Post subject:

imagine this, we did some research on how to use a fishfinder this weekend because I was frustrated by the 40ft reading in water I suspected was 200ft. down riggers were pushing 70ft and clearly not dragging bottom so I knew things were wrong.

I experimented with the GAIN settings on the depth sounder/fish finder. I tuned them WAY back to 50%, then every few minutes I turned the gain up about 5%. I think at 90% I found that it would read weird again, but around 87% it was suddenly consistently accurate with no weird settings.

so just another tool for the tool box. if you're sounder if giving you weird depth settings, maybe turn off the auto gain and try turning it down (70% is probably a low enough starting point from my limited experience) and then turn it up a little at a time. when the gain was very very low my depth was very accurate but it shared NO other objects, no fish, etc. I'd rather have an accurate depth reading and no fish reading, personally. I dont even believe what it says about the fish anyways.... Rolling Eyes

Aurelia · Posted: Tue Jul 23, 2013 12:53 am Post subject:

Mark, I have installed and used a couple of Garmin systems and I regularly see misreadings of depth. I however, have always been able to at least loosely link the occurrences to fouling of some kind, water turbulance from wave patterns, loading or boat lean and if the transducer has changed angle slightly, that will have an affect of course. A piece of debris has re-angled mine a few times and that made it act strange until I could eyeball and adjust it properly. A reboot can always help a software error but I would really look for a physical cause first.

Also, as you have been out lately, you no doubt have seen all the green mats of algae floating around. They send my transducer into fits as well.

Greg