Originally Posted by doug86
Obviously, this is a personal choice, ...............
To me, it seems to make the most sense to be able to compare the actual depth
as reported on my depth sounder
to the charted depths. I think one should be in the habit of thinking of the actual depths rather than how much is under one's keel
Originally Posted by wolfaroo
exactly! whichever method you use will either involve a quick sum to get total depth
or a quick sum to get clearance under keel
As many have said before it is purely personal preference... I prefer clearance under keel too because that's the most important number!
If you hate 'math'(well, sums!)... When you are using for navigation
you have to add datum+current tide regardless
of how your sounder is calibrated so you might as well chuck all the 'math' in together (datum+tide-draft = sounder, and sounder=clearance)
It can be a useful fix line (contour) and is VERY useful in heavy fog
Yes, of course it is personal choice but those who say they want to compare the indicated to the charted depth always have (as wolfaroo and some others point out) to do the maths of charted depth plus current
tidal stage. Calculating the state of the tide can be difficult in some areas so having to add your draft
into the equation surely is not that difficult.
Personally I use depth under the keel as this is the most important number for me and the one that should be crystal clear in an instant. A quick glance at the sounder tells me right away what I need to know.
If I am navigating by charted depths, I always have some time up my sleeve to do the sums of charted depth, datum, current
stage of tide and observed depth.