Topic: New member - Ducer location input appreciated please

[Coach62]

Hello all, well my Lowrance just crapped out for the second time, of course just out of warranty again.  No problems as I've been wanting an excuse to buy another HB with SI.

I'm planning on putting the new ducer in the same location as the existing screw holes as shown in the photos.  My unit is a 998C HD SI Combo.

I do a lot of bay fishing in the 4-6' depth range, and go offshore in the gulf to 50' deep or so.  I typically cruise around 35 mph and of course want it to work well at least at that speed, up to 50 mph would be great.

I'm looking forward to the down imaging feature also.  One more question, has there been any improvements in the speed in which the SI works?  With my old unit it only worked up to around 5 mph or so.

As you can see the ducer would be about 12" from the center of the hull.  The motor is about 10" from the hull at the bottom with 0 trim.  I typically don't run a ton of trim as the Verado is a great motor, but heavy as you all know.  I typically run it at trim position 2 or 3, which may be another inch or so, but that's an estimate.

My question is, does this look like an acceptable place for it?

Thanks in advance for the help.

[ITGEEK]

From what I can see, that looks to be about
the best spot for the transducer.

Of course, you won't know until you test it.

Chuck suggests that you use double sided tape
to test before permanently mounting.  This is a very
good idea.

You may not be happy with high speed readings from your
SI transducer.  Most users aren't.

So, you may have to add a shoot through the hull second transducer
to get good depth readings at high speed.

Again, you won't know until you test  it.

I think SI still requires speeds below 10mph to work well.

[Humminbird_Greg]

I would be very cautious about any high-speed testing with a transducer that is held on with double-sided tape!  It may not hold and you certainly don’t want that big monster to take a trip through your propeller let alone have to buy a replacement!

That does look like your best location though.  Once you are happy testing it with double-sided tape at low speed; permanently mount it with screws and test it at high-speeds.  It may or may not read at high-speeds.  If it does not you can try lowering the transducer and adding a little angle on the transducer (drop the back end down – no more than a few degrees). If that does not help enough your best option is the AS-Si-DB-Y cable and XP-9-20 transducer that ITG was referring to.

[Coach62]

Thank you, that's what I thought.  The trim tab is the limiting factor here as I can't move it too much more to the starboard.

Question regarding the shoot thru hull ducers please.   How much detail / resolution do you lose with those?  Do you gain a significant amount going with the full blown thru-hull units?  I would never personally install one of those, I'd rather pay a pro for that.

Thanks again. 

[ITGEEK]

As far as the shoot-thru transducers, I have never
used one, but I can imagine if you are shooting through
fiberglass, then the signal hitting the bottom, then going back through
the fiberglass, back up to the transducer, that you are going to be
losing something.  I think the shoot-thru the hull transducers are mainly to
get a depth reading at high speed.  They CANNOT be used
for side-imaging.

Now, if you are using 2-d or DI (with true DI crystals), on the
shoot-thru transducer, I would think the image would be much
weaker than say a transom mounted transducer, where nothing
is blocking the signal.  Again, I have no personal experience using
one.

I hear that the thru-the-hull transducers give the best readings
because that are mounted mid-way, or a little aft of mid-way on the
boat, where there is less turbulence than on the transom.
Again, I have no personal experience using thru-the-hull transducers.
I have also heard that high-speed readings are good, because the
transducer is still in the water even if the boat is on plane.  I guess it
depends on how heavy your boat is, and how powerful an engine
you have.

And yes, If I needed a hole drilled all the way through my boat,
I'd let a professional do it too.

The main problem with a thru-the-hull transducer (as I see it), is if you hit
something hard enough to completely break off the transducer,
you may sink your boat.

[sonar2000]

The hdsi transducers do not work well at speed so we are only suggesting tape to find a spot where they will work best at trolling speeds..
for speed reading it is best at thru the hull or a 2d transducer..
Chuck

[Gator]

This is somthing I've been wondering about. I have a 2d transducer, if I mount it how do I hook it up to my 998c SI??? and still keep my SI transducer hooked up. Do I have to plug in one than unplug it and plug in the other? Do i have to buy a "Y" adapter? I hope this isn't a stupid question.

[Bob B]

There is a Y cable.  part # AS SIDB Y.

[sonar2000]

Y cable or a TS3 switch.. In our situation we prefer the TS3 switch..

Chuck

[Humminbird_Greg]

When using a shoot-thru (I like the term “inside-the-hull”) transducer, there is some signal loss.  How much depends on the hull construction and how good of an installation was done.  This is why I always recommend on-water testing of the mounting location.  I have heard from far too many people who have taken their boats to a “professional” who installed an inside-the-hull transducer that gave poor results only to find out that they looked in the back of the boat and decided to just put it there… without having any on-water testing of the mounting location.  Even on the same make/model boat there can be variances in the hull construction from one boat to another that would require the transducer to be mounted slightly more to one side than the other.  Once I helped install inside-the-hull transducers on 30 identical boats for a tournament.  We had to test each boat to make sure that the location would work for each boat.  There was up to a four inch difference in mounting locations on some boats due to differences in the hull construction.  With a good installation I have heard that you can have up to a 20% signal loss.  Sounds like a lot but many would never notice this loss.  For those that do you can often just bump up the sensitivity setting on the unit to make up for this.

Not sure of the boat that you have but a true Thru-Hull transducer can also cause problems when you are on or trying to get on-plane.  It does stick down into the water and will change the characteristics of your boat’s hull and how it moves through or over the water.  Anything you hit that will shear one of these transducers from its bronze or steel reinforced shafts will probably also hit your boat’s motor and the result will not be pretty.

[Coach62]

Thanks Greg, you raise some good points, and raise another question at the same time.

If you are looking at a 20% or greater signal loss in a shoot-thru-hull ducer, how is that better than a transom mount ducer?  Maybe I'm just not understanding the limitations of the T.D. that comes with my unit???  Is the transom mount unit really that bad?

[sonar2000]

The signal loss is the shoot thru the hull transducer.  The transom external mount does not have the loss. It is however subject to cavitation, reflection and or side blockage.

Chuck

[Humminbird_Greg]

Coach62,
Its better due to its location in that it will give better high-speed depth readings.  On some boats it is impossible to find a transom mount location that will allow for high-speed water depth readings.  It also protects the transducer from being hit by stumps, rocks and debris.  The only limitations with the HDSi transducer that came with your boat is that due to its size and the direction of the Si sonar beams; it is harder to find a location on the transom that would allow for both high-speed depth readings and unblocked left and right Si sonar.  Many will instead install the HDSi transducer where it is more protected and yet can perform the Si sonar function with no blockage to the Si sonar beams and install an XP-9-20 transducer and AS-Si-DB-Y cable for better high-speed depth readings.

[freezerfiller]

 I'm interested in the shoot thru transducer as well.   How does the Y cable work? Does the unit default to the SI transducer and only switch to the 2D ducer when the signal fails?  Which shoot thru part# is recommended?  Coach,  rather than risk drilling holes in my transom trying to find the right spot, I put a small piece of King starboard in that area with some 3M 5200 sealant.  then I can screw into that without putting holes in my transom where water can get in one day.  5200  takes a long time to set up, but once it does it's there. 

[Humminbird_Greg]

We recommend the XP-9-20 transducer for this.

The Y-cable (AS-Si-DB-Y) is nothing more than wiring and connectors. There is no switching from one transducer to another.  Within the HDSi transducer you have are the elements for the Si/Di sonar, the element for the 2D sonar and the temperature sensor.  The cable has connections for all of these.  All the AS-Si-DB-Y cable does is connect only to the Si/Di elements and the temperature sensor.  All of the 2D sonar will always come from the XP-9-20 DualBeam transducer.

If you want to be able to select which source of 2D sonar you want to use (from the HDSi transducer or the XP-9-20 transducer) you will have to instead us the TS3 Transducer Switch.