Understand that the DSI sonar ping is a narrow fan shaped deal, that is shooting at a 45deg angle @ 800kHz setting or 75deg angle @ 455kHz.

In 12 fow ... that brush could have been anywhere in the signal ... and the 800kHz signal would be about 10ft wide - the 455kHz signal would be around 18ft wide.

Without the unit having GPS capability, you're stuck with having to drop markers. And like Catfan says ... you want to be dropping them as soon as the image comes on the screen. To which I would add .... have more than one marker ready to drop/throw, and drop/throw them off each side of the boat so that you have more than one point of reference to come back to.

Here's where I got the angle/distance references : (thanks to Kosmo)





... cp