I currently have a HDS-7 and a HDS-5.

The HDS-7 in the back of the boat uses a thru-hull transducer and works great for showing me the depth even at full speed, but it is very poor for showing any structure or fish arcs.

My question is, is there a way to have my HDS-7 use the thru-hull transducer when driving, then switch over to trolling motor transducer that the HDS-5 uses while fishing?

What would I need to buy in order to do this?

Would the LSS-1 structure scan allow me to do this?

Or would the Navico expansion port do it?

Is there any reason someone would have both the expansion port and the structure scan? It looks like the structure scan does everything that the expansion port does plus the structure scan?

One last thing, does anyone use the broadband sounder? is it any good for bass fishing?

Regarding your HDS 7 and the returns you are getting, it could be due to the quality of the shoot-thru mount. Instructions (page 13 of link below) must be followed to ensure maximum performance and highest-quality returns.

http://www.lowrance.com/upload/Lowrance/Documents/Manuals/Skimmer_xdcr_0147-582_041703.pdf

Also be sure to have the current software (3.5), check at Menu, Menu, System, About.

Here are some sonar settings that may improve returns. First, under Sonar Settings, select Shallow Water (for our purposes this is water < 100 feet deep) (the default is General Use) and set scroll speed to normal. Also, under Installation select your appropriate transducer. Under Sonar Menu, I run Ping Speed at 18. Colorline I like at 85.

For shallow water, especially around grass, I prefer color palette 1. For deep water or with lakes void of grass, I like palette 13 (bottom color tracking in the older units, helps separate fish from the bottom/cover).

To share 2D ducers between units (network sonar), all you need to do is Ethernet-link them (yellow cable). Then, you select ducer source in the sonar menu.  You can do this directly from unit to unit, or link them thru an LSS box or Ethernet expansion port. Your LSS has three Ethernet ports, so it will link three devices. You would only need the expansion port if you were linking 4 or more devices.

The broadband 2D sonar is built-in to the HDS units.

Thanks for the tips on what setting to use, I could never find any that I liked, I will try those.

I did follow those instructions when I mounted a skimmer type transducer the same ones you linked.

I have never seen a fish arc on this locator tho.

Are you saying all I need to share the transducers is buy a yellow cable and connect the 2 units?

Is there a way to have the shoot-thru hull transducer always show the depth on the map overlay, and use the other transducer to show sonar, without changing settings all the time?

Yes, you can share 2D sonar ducers by directly connecting the units with an Ethernet cable.  The depth overlay will change with the corresponding 2D ducer you select.