It's important to realize (and you probably already do) that the 2d sonar beams are cone shaped and the DI sonar beams are thin slices....



A discernible DI image is plotted onto the display by pinging a "new" slice of water at each ping of the sonar and then stacking those pings onto the display to "build" the DI image....therefore moving would be the optimum use of DI...

(this is not to say that DI cannot be used stationary but the DI image would be more of target echoes stretched across the screen because the the unit would be pinging the exact same slice of water each time...)

A lot of vertical jiggers use the DI to travel completely over the structure to "paint" a discernible DI image, and then reposition the boat to vertical jig with 2d or a buoy marker tossed over the structure...

Rickie