There is a different Y connector to run two SI transducers to deal with obstructions. I’ve seen that primarily on inboards.
I’d guess that the vast majority of users, particularly those with tin boats, do NOT run two transducers. It’s really not necessary, as a good SI transducer placement will provide all of the sonar data you need well into the 40 mph range. Here’s a screen capture from my Ranger 1860, running a single transducer, and collecting sonar data at 41.5 mph.