I don’t think that’s exactly what was said; here, at least. I think Don’s point was that if your depth sounder fails, you can know the depth under you from your chart, if you have your chart position. If you are coming toward shore and your sounder goes out, but you have a chart track, position, you’d know how close to approach, etc., if it’s all charted correctly. With fog, it’s the same except that there is no evaluating the situation further looking toward shore for changes in water hues, or other indicators. Without the sounder in fog, you‘d have ONLY the plotted position on which to rely, although possibly with fog signals. Everyone here voicing an opinion agree that relying on a sole source of “input” while piloting is not best seamanship. Lacking sounding you would have no confirmation of your depth. Breakout the lead line (or digital) before coming closer. We’re talking here about a fm or more of variance, not a foot or two.I've heard before about how you could supposedly determine your position from depth soundings. What am I missing - looking at a chart I don't see how that works.
Here's a position from a recent trip I took. I was inside the red circle, reading 14' of depth. It was an incoming tide supposedly 1' above MLLW, so I should be looking for places charted as 13'. So I could've been anywhere along the green line, which is not a very precise position, and not correctly where I was -
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