My depth sounder is set to display the depth of the water. Over here in the UK, it seems most are set to depth under the keel. Both seem to have some logic to them - but I can't see how depth under the keel is helpful except when in very shallow water... in which case, I just have to subtract 2M from whatever it displays.

When anchoring, I want to know depth - not depth under the keel. When following a contour line, I want to know what depth it is - and even then I have to work out tide heights, etc....

Why the prominence of depth under the keel over here??

Bill Balme