A depth sounder is a good piloting tool in that it reads the depth and changes giving you one more confirmation (from soundings on chart) of your location.Giro,
How helpful is a depth sounder in that situation? How far ahead does it scan? Is it enough to stop or steer away from such an obstruction or are you looking for the clearance start dropping as the bottom is approaching? I am not familiar with depth sounders or their operation, but I figured they wouldn't protect against sudden obstacles, only upcoming clearance limits.
Snoopy
Plus as an anchoring tool it helps us gunkholers to find the best spots, on the fringes. You go real slow though, it doesn't tell you about the ledge just under your bow.