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Old 08-05-2011, 04:35   #46
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Re: True Depth or Depth Under the Hull ?

Originally Posted by doug86 View Post
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.

my .02
Originally Posted by wolfaroo View Post
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.

Happy sailing
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.
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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Old 08-05-2011, 08:50   #47

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Re: True Depth or Depth Under the Hull ?

If you're gunkholing or running shallows that frequently shift, depth under the keel is probably what counts because the charted depth is obsolete before the ink dries on the chart.

Of course if you're trying to run a contour or use depth for piloting, depth under the keel isn't as useful as total depth, but if you're in tidal waters, you're going to have to do some simple path to offset your depth from the chart, according to tide state, anyhow. Six of one, half dozen of the other, makes no difference as long as you know just what the numbers are reflecting.
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Old 09-05-2011, 14:12   #48
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Re: True Depth or Depth Under the Hull ?

Thanks everyone for your thoughts. Sounds like the "bottom" (sorry couldn't resist) line is know how the equipment is set. A good point was made regarding anchoring and the amount of rode needed particularly since the more shallow the area the more variance you would have and potentially less holding power.
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Old 10-05-2011, 13:10   #49
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Re: True Depth or Depth Under the Hull ?

I have the original depth sounder that just spews the depth from the transducer which i need to add my keel, and I just installed a new one that is hooked to my chartplotter which I set to my keel plus one foot I draw 4'3" so it goes off when I am in water shallower then 5'3", so I know my safe limit at a shoreline lunch.
This way If someone reads the number to me while I am on the bow it will be exact depth under the keel.
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