Topic: 798 SI imaging while moving

[hgv]

I have a 798 SI DI HD ........ I have the transducer mounted on the transom, dead center of the boat. Works great where it is (see picture). Of course when I start moving and get on plane it does not due to being out of the water.

I would like to be able to at least use the DI while moving so I see if I run over a school of fish. The boat came with a in dash Lowrance thru hole system. Towards the back of the boat, inside the boat, in the bilge area is a transducer that appears glued to the bottom of the hull and looking from the outside under the boat you can see well something. But it is a old circle (??) display.

So questions:
1. Can the 798 be setup so that DI works while moving? If so how?
2. At what speeds will the DI work?

Thanks in advance

[Humminbird_Greg]

In the 798 units (and all of the Side Imaging units that Humminbird makes), the Di sonar comes from the Si sonar beams.  The Si/Di sonar will work at any boat speed but only as long as you can keep a steady supply of water flowing around the transducer.  Any air bubbles that flow across the sides or bottom of the transducer will disrupt this.  Now each boat is unique in its construction, set-up and loading so there is no one answer as to what speed the Si/Di or even 2D sonar will work up to.

On your boat to get Di sonar at faster boat speeds you will need to move the transducer down to the lowest step (if there is room for it).  Hard to see in the picture that you posted but it looks like the drain plug and livewell intake screen covers are in the way, so you would have to end up offsetting it to one side or the other.  If it is offset too far the hull itself may start blocking one side of the Si sonar.  In this location it could possibly cause an air cavitation pocket to form which would disrupt the water flow through the propeller and possibly into the cooling water intake of your motor.

Most usually mount the Si transducer where it works well at low speeds and then install an inside-the-hull DualBeam transducer for 2D sonar readings at high-speeds.  Doing so also requires the use of either the AS-Si-DB-Y cable (this is what most use) or the TS3 Transducer Switch.

[hgv]

Yes I believe your recomendation about putting a through the hull transducer is the way to go. I do not want to lower the transducer anymore on the transom and plus as you saw the drain plug and screened intakes are in the way


Thanks for the advise and for responding, I will go look up that cable at humminbird's website.

[hgv]

How does the Y cable work? If both transducers are connected which signal will it use? How would it know to use the rear mounted transom for SI vs the thru hull

[hgv]

Correct me if I am wrong ........

If I get a Y cable to use with my 798 SI HD then I also need to get a dual beam transducer for my thru the hull mount so I can read the bottom while moving. So the SI would come from hte transducer on hte transom while the DI will come from the thru hull

[hgv]

this transducer ........ XFM 9 20

[hgv]

although the 798 is not listed as a device to use it with ??

[hgv]

As mentioned above I have a thru hull mount now but it is a Lowrance. I believe I can remove it and replace it with the XFM 9 20 then use a Y cable (AS-Si-DB-Y) to connect the transducer that came with my 798 SI HD presto DI while moving.

How fast can you go and still get a good reading of what is under the boat with the thru hull mount?

[Humminbird_Greg]

Slow down there hgv…

As I explained above: the Di sonar comes from the Si sonar on the 798 Si units.  So at whatever speed you lose the Si readings at will be the same speed that you lose the Di sonar readings at as well.

[We make DI model units that have a different type of DI sonar which can be mounted inside-the-hull of a fiberglass boat and could work at a higher speed due to where the transducer can be mounted.]

The XFM-9-20 can work with the 798 Si units and would only provide the DualBeam 200/83kHz 2D sonar for it.  However, the XFM-9-20 is a Flush Mount transducer which requires a 2-inch hole to be drilled through the bottom of the hull of your boat.  You instead need to look at the XP-9-20 “shoot thru hull” (I like the term “inside-the-hull”) transducer.  It installs inside of the hull of your boat using epoxy – no holes needed.

The AS-Si-DB-Y transducer splitter cable works by connecting only to the Side Imaging and Temperature Sensor connections of the Si transducer.  It also connects to the 2D sonar of the DualBeam transducer (in most cases the XP-9-20 I mentioned above).  Both combine to bring the 2D, Si/Di and temperature into your 798 Si unit.  The 2D sonar will always come from the inside-the-hull XP-9-20 transducer (if that is the one you install).  The Si/Di sonar and water temperature readings will always come from your Si transducer.

[hgv]

Thanks for the input.

The shoot thru the hull, does sound better than drilling a hole in hte boat. There is already a thru hull Lowrance transducer installed from the previous owner. I could try and remove it and install the thru hull but I measured the hole and its a little shy of 2".

Can a boats fiberglass be too thick as to prevent the "shoot" thru (inside) the hull transducer?

[Rickard]

Remember,
 
There are Lowrance (actually Airmar) to Humminbird adapters for some transducers. Perhaps the existing thru-hull transducer can be connected to a Humminbird unit.
 
Rickard

[hgv]

Hmmm but I would have to know what brand transducer it is not sure I can find out that info from the part

[Rickard]

Also several other sonar brands use, or can use, Airmar transducers. Here one can find out: http://www.airmartechnology.com/2009/marine/product-search.asp?Type=FF
 
Rickard

[Humminbird_Greg]

Yes to your question about the fiberglass being too thick.  I think we say (in general here) less than 1-inch of solid fiberglass.  Any other material, like a foam core, wood or other reinforcing or air containing material, may block the sonar signal.

Check the cable of that transducer for a label that may have some ID numbers on it.

[hgv]

The cable to the thru hull transducer that is attached to a lowrance flasher has a M0007 written on the cable at the transducer end. Up under the dash is a label on the cable labeled TH-FWBK wide angle.

There is also a connector whre you can uploug this cable fronm the flasher, it is a 2 pin connection

[Rickard]

This must be the Lowrance TH-FWBK #000-0090-75 transducer. This is a single frequency transducer that should be fed with 192 kHz. It can probably be operated at 200 kHz too and all circular transducer elements (all traditional transducers have circular elements) have two frequencies even if that´s not stated in the specs. The second frequency is always lower and use to be 50 kHz. If this was my project I would try with connecting the unit using the middle and the upper sockets in the unit (ground and 200/83/50 kHz). It does'nt matter which socket one connects to which pin in the transducer connector. I don't know if there is an appropriate transducer/frequency select option in the 798, but I would search for something that makes the unit operate at 200 kHz and 50 kHz and see if the system works.
 
Rickard

[hgv]

Here is the exact unit .................

http://www.ebay.com/itm/LOWRANCE-THRU-HULL-WIDE-ANGLE-TRANSDUCER-19-000-0090-75-TH-FWBK-MARINE-BOAT-/230823222559

[hgv]

thought I would update the forum with the process. So I purchased the humminbird thru hull transducer  (XFM-9-20) and Y cable. I knew I had to get the old Lowrance thru hull transducer out which was 1 3/4" diameter and replace / enlarge the hole for the 2" humminbird. Purchased a 2" hole saw and assuming I could use the installed lowrance thru hull as a guide I proceeded to try and drill thru the installed tranducer. Well, that did not work not sure what is in a transducer but it is very hard. Seeing that I could not use the tranducer as a guide a small amount of nausea did set in. (other words oh crap) The sealant that was used to install this original tranducer (in 1996) was pliable on the inside of the hull and I was able to scrap it all out up to the threads on the existing thru hull transducer. Now with the realization that the old thransducer had to come out I took a 1" PVC pipe which fit down in the transducer from the inside of the hull perfectly. Then using a rubber hammer I gently tapped on the 1" pipe, with very little force I was able to drive the old tranducer stright down thru the hull. Now I have a nice hole in the hull   I then went to Lowes with the old plastic nut from the old transducer where I found a wooden dowl that fit the cap perfectly. Back at the house I cut about 4" off of this 4' dowl. Then I drilled a hole dead center of this 4" piece so it would fit down onto the drill guide bit in the hole saw. Pushing the 4" dowl into the hole of the boat and using this as a guide I was able to drill a perfect 2" hole in the boat. The thru hull Humminbird tranducer fits perfectly. Using 3M 4200 sealant I then proceeded to install and tighten down the transducer. Looks great! Now I just have to route the cable to the front of the boat which I believe is a bigger pain.

[Humminbird_Greg]

Wow!  I was worried how your post was going to end there for a few lines or so…
Glad you got them changed out and I will have to remember how you did this.  I appreciate you sharing this with all of us.

[hgv]

Upgrade complete, routing a cable up the side of a bass boat is a real pain in the you know what!

Anyway leak test comes tomorrow, will try to get some pictures too.

[Humminbird_Greg]

Upgrade complete, routing a cable up the side of a bass boat is a real pain in the you know what!

Arm?
(Thinking of all the fiberglass I have picked out of my arm over the years…)
 

[hgv]

That stuff is nassssty

[hgv]

I have attached a picture although hard to make out. I get a good reading up to around 35 mph then apparently there is too much distrubance above that speed.