Just installed a Raymarine ST40 depthfinder this spring and find it unreliable. I ran aground in what the depthfinder assured me was 8 feet of water beneath the keel, which draws 3 and a half feet.
Or it steadily displays a tenth of a foot of water below the keel in a channel that the charts say is 5-8 feet deep.
Can turbulent, choppy water confuse a depth finder? That hasn''t always been the case when a reading was clearly wrong, but it is usually what I get when I cross the bar outside my canal into the shallow bay.
2 possibilities? The manual recommends that the depth finder get wired to the house battery instead of the engine battery, but I don''t have a house battery and there''s no place to put one, so its on the engine battery. Manual says that the settings can be lost when the engine is turned on, but so far the settings I programmed are still there.
Other possibility may be that air is trapped in the silicone caulking I used to stick the transponder to the hull. There''s a level place in the hull with no core that was intended for an inboard transducer. But if it worked fine initially, how would air have been introduced?
Any thoughts? I haven''t called Raymarine service yet.