legend,
The TS2W Transducer switch will allow you to switch (manually) between two transducers. Most common application, you could have an SI transducer on one side and a in-hull transducer (2d) on the other and be able to switch over to the in-hull at higher speeds for better 2d depth readings. Or even have two SI transducers. I have a switch where I can switch over to a second SI transducer mounted on a towfish without having to disconnect the cables.
From Humminbird Site:
Transducer Switch
This switch allows you to use two transducers on one depth sounder. The cable going to the depth finder is approximately 5 feet long and the two cables going to the transducers are approximately 20 inches long.
The SIDB Y Splitter cable is mainly used for the first example above. It will split off the DualBeam "2d" portion from the SI transducer and hook into another transducer to take the dual beam from it. Again, usually for better depth readings at higher speeds. The 2d depth is taken from the second Dual Beam transducer only and the 83/200khz on the SI transducer is no longer used.
From Humminbird Site:
Side Imaging Splitter Cable
Y Cable - Side Imaging and Dual Beam - allows you to use two transducers on one unit without the use of a transducer switch. For use with Side Imaging products only, in conjunction with a dual beam transducer only. For improved high speed performance for bottom tracking.
Robert