[TG] [TG11] Odd readings from an ST800 on an ST70

[Tom - Raymarine - Moderator]

Hello RKonGB,

What that sounds like to me is an echo off the keel. We've run across a few cases. The attached extracts from our Dealer training give a little background. This is, in my experience, the usual cause for a consistent, false, shallow depth reading on instrument systems and happens because the beam on these transducers is so wide that it can easily reflect off boat structure. Backing the boat up directs aerated water across the transducer, blocking the echo and breaking the 'bottom lock' on that false shallow depth. When the aerated water goes away, the system can then reacquire a true bottom lock afresh.

Regards,
Tom