Losing depth readings when I go fast

[Teach13]

Hey guys.

I bought a used boat last June that came with a Humminbird 998 with side imaging. All last summer everything worked perfect. But starting last fall I noticed that every once in a while my depth readings would go to 1.5 ft when I opened it up a little. But it was kinda off and on.

This spring I went up to the rainy river and as soon as I went master than 13 mph I would lose the depth reading.

A few things to maybe shed some more light:

It does have the high speed ducer and the SI ducer

It reads well at slow speeds.

Side imaging and gps still work fine

I did check the ducer and it really didn't appear to have been knocked...and it's not loose

Am I just looking at a bad transducer? One of my buddies thought it was a cold water thing?

Thanks guys.

[Walleyehooker]

Sure it didn't get tilted up or down? Sounds like its out of place to me.

[Teach13]

I guess I'm not totally for sure. But looking at it it sure looked fine.

[jentz]

Down load the tuning a transducer instructions from HB.If its reading slow but not higher speeds its not adjusted correctly,set in a bad position,Motor interference,tilt onit got to be there somewhere

[JeffB]

I agree that your transducer is probably slightly off, it doesn't take much. I had that problem with mine. I had to adjust it several times till I got it right.

[Teach13]

OK...how do I check that?

It was weird to me that it worked then didn't. I didn't hit anything. There really isn't much movement on the ducer itself (if any). When I look at it it looks to be level.

Maybe I have to have a buddy drive the boat and I can try to toy with it to see if I can get a reading...but that sounds so unsafe!

How can I check that safely?

[TruthWalleyes]

Your transducer is most likely mounted too low and you are getting cavitation above 13mph causing the problem. Sonar doesn't work well through aired water. You've probably got a nice rooster tail going on as well. Read through the HBird instructions on mounting a transducer...There's only about 14 pages or so

Tilting the ducer up or down will also cause the problem. The transducer should be level WHEN THE BOAT IS FLOATING, not necessarily when it is on the trailer.

[Teach13]

OK...thanks guys.

I will take a look at the manual. I will also look to see if its too low. Doesn't it seem weird, though, that it worked perfectly fine in the summer (including trips to LOW)?

To me it seems like...if the ducer was indeed mounted too low...that it would never have worked?

Why the change? I guess maybe it got knocked or something?

[jentz]

I found the main problem is where the black ducer rings on the mount arent set for the correct transom angle.Thats the main starting point,Then while the boat is in the water the ducer has to be level with thhe water and bottom not the boats bottom.The next step is the line on the ducer set level with the boats transom crosswise.

The instructions NEED to be read.Then go through it step by step from the beginning.Of where it should be set to transom angle with the black rings in the proper peg for the angle of transon.

[TruthWalleyes]

Did you change props? Different trim on motor? Added any tabs to the rear end of the boat? Increased weight or weight distribution changing boat angle?

Cavitation or not level are the two things that can cause your problem.

[PerchJerker]

We work on a lot of transducers and there's two common problems that could be causing what you're experiencing .....

1. The tilt angle on the transducer might have changed, or might have been wrong to start with. Try tilting the back of the transducer down slightly .... this put the face of the transducer in a smoother, cleaner flow of water, and solves A LOT of problems reading at high speed. Most of the illustrations in the manuals show the transducer tilted up in the back ..... in theory this gives you the best fish arches while ON PLANE (but not while not on plane) .... and in reality it can cause cavitation on the face of the transducer and that will cause you to lose your bottom reading.

2. You might need a new transducer. They wear out. And while they're wearing out they get weaker and less sensitive. This happens to all transducers eventually, it might have happened to yours now.

One other thing that might be going on, although is not as likely to cause this problem .... did you change the load in the boat or the way the boat runs .... ie. different prop, raise or lower your motor's mounted height, add/remove/relocate batteries, add/remove/relocate passengers while running on plane, etc. Weight and load in a boat might affect the reading.

Good luck getting it figured out.

[Teach13]

Thanks guys for the help. A guy a cabelas also said to make sure it has updated on the computer. I will look at all of these and hopefully I can figure it out.

Thanks again!

[TruthWalleyes]

UPdates will have nothing to do with it.

[thatoneguy]

I have the same issue occasionally with my 898cSI.

[TruthWalleyes]

This will be a good page for you guys with hi speed problems:

http://www.sternmate.com/Where.html