Topic: Incorrect Water Depth at 40 MPH

[KickSomeBass]

  I have a new 798 ci HD SI that I just installed.  I ran out to my favorite river to test it out.  Ran the boat at about 40 MPH and while running at this speed the water depth read 1 foot.  I know I was in at least 5 foot of water.  Have I done something wrong or this normal?  The unit I previously had (Garmin) showed what I think the actual depth was.  Any help out there???

KsB

 

[mt72916]

some questions to help determine your situation.
are you running the original (SI) transducer that came with the 798?
is it mounted on the transom or jack plate?
are you running a regular 2d transducer in the bilge with a Y cable along with the original (SI) 798 transducer?

[KickSomeBass]

This is a brand new unit (2011 model).  This is the only transducer I am running, except for on my trolling motor and these unit are not connected.  I have the 798 transducer attached to the transom--not to the jackplate.

KsB

[sonar2000]

It sounds like cavitation or air introduction. If the unit works at slow speed then you probably have something disturebing the water around the transducer. This is especially when using the HDSI transducer.
Or a large puck...
chuck

[KickSomeBass]

Any fix for this situation?

KsB

[Trytoofish]

Lower it and make sure the front is a tiny bit higher than the rear. Most poor high speed readings are from out of adjustment transducers. They need to have a clean stream of water in contact at all times. row of rivets will cause turbulence's.avoid them.

[KickSomeBass]

  I'll take it out on the water tomorrow and see if I still get the same reading.  If I do, I'll lower it.  Thanks.

KsB

[sonar2000]

KSB....these large transducer are very sensitive to location for each boat. A lot to take into consideration for the mount location.

Go to the search tab at the top of the main menu and do some forum searching on transducers, mounting, etc.  You will find a lot of hits.

Also you can go into the image gallery and look at pictures dealing with mounts and location..

Chuck

[Humminbird_Greg]

KsB,
Is this on a fiberglass or aluminum boat?

[KickSomeBass]

Fiberglass.  I have a Stratos Bass Boat.  I didn't run the boat motor today because there were too many fish to be caught. 

KsB

[Roddy]

KSB; Post some pix of your instal.

Enjoy Roddy

[billius]

I have always had that problem with the HB's on my last two boats. I had a 797 on my Baycat and have a 997 on my CougarFTD. Both units lose the bottom around 45-50 mph. In both cases the SI transducer was on the transom and the other one is fiberglassed into the hull in the bilge. It's not a big deal except when I'm on a strange lake. I have to be sure to run around 40mph so I can keep an eye on the bottom depth.

[RGecy]

Definitely post some picts of your install so we can see whats going on.  Straight on from the rear and from the side also.

There is a fine line with getting good depth readings at higher speeds with the SI transducers, depending on your hull type.  I have a deep V with no steps and had the same issue initially, but solved it by dropping the transducer down lower in the water.  However, now I have a rooster tail.  But I rarely lose bottom lock.

A lot of the bass boats have a step at the rear that when on plane will keep the transducer out of the water.  So you have to either mount a second in hull 2d transducer or put the SI transducer down on the lower part of the step.  Of course now this leaves it exposed to stumps, etc.  But solves the problem.

Hope this helps.  Post us some picts and we'll see if we cant get you fixed up!

Robert

[KickSomeBass]

I'll post some pics next week.  Got rear-ended on HWY 98 in Navarre yesterday and got a concussion and jacked up my neck.  Need to see the chiro first to make sure their isn't any long term damage...

KsB