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Old 06-05-2011, 15:46   #31
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Re: True Depth or Depth Under the Hull ?

Oh, come on you guys... surely you can remember what your draft is, even under duress!

Comparing the depth reading to your known draft isn't really "doing math", even by current educational standards.

But, I agree that one should do it whichever way is most intuitive for YOU... even if it disagrees with my way. Of course, then it would be wrong...

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Old 06-05-2011, 16:52   #32
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Re: True Depth or Depth Under the Hull ?

I have other reasons to use under the keel, I have the transducer stuck to the inside of the hull on a side, so it is not pointing straight down but at an angle, maybe 30* and about 1 1/2 below waterline, so if I just set it for 0 offset it's still less then surface,
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Old 06-05-2011, 17:11   #33
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Re: True Depth or Depth Under the Hull ?

I go with the water under the keel, so I know when I am going to hit. So I Don't have to do the math...
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Old 06-05-2011, 17:12   #34
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Re: True Depth or Depth Under the Hull ?

Quote:
Originally Posted by Jim Cate View Post
Oh, come on you guys... surely you can remember what your draft is, even under duress!

Comparing the depth reading to your known draft isn't really "doing math", even by current educational standards.

But, I agree that one should do it whichever way is most intuitive for YOU... even if it disagrees with my way. Of course, then it would be wrong...

Cheers,

Jim
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Old 06-05-2011, 17:20   #35
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Re: True Depth or Depth Under the Hull ?

Total depth for us. I agree with the inferences of one of the posters above who suggests that you put a label on the instrument to inform users of the calibration.
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Old 06-05-2011, 19:36   #36
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Re: True Depth or Depth Under the Hull ?

If math was the deciding factor, wouldn't be just as easy to add the draft? For me, I like under the keel as when I tell someone to watch the depth, its "When it drops less the 5' let me know. If it's at 2' - start yelling. Also, when we dive off the boat, its the depth plus the draft = safe. I personally can't see where I'd be actually navigating using draft comparisons to a chart but just add it together.
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Old 06-05-2011, 19:52   #37
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Re: True Depth or Depth Under the Hull ?

I have two depth sounders on board being set by previous owners and yes they had them set for both conditions! One read true depth the other read under the keel - why?

I use my DS to confirm or reference my location on charts at times - to add or subtract, why?

As these instruments fade away in time I will upgrade and set both units to true depth.
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Old 07-05-2011, 06:02   #38
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Re: True Depth or Depth Under the Hull ?

Well put Palarran
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Old 07-05-2011, 07:14   #39
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Re: True Depth or Depth Under the Hull ?

It seems like the "right" answer is less important than being clear with anyone driving the boat what the number means. Since it's going to be the admiral or me driving when there's any realistic prospect of the depth and the draft lines crossing, it's not a major problem. FWIW, we use true depth and set the alarm for two feet below our 5' keel.
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Old 07-05-2011, 09:35   #40
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Re: True Depth or Depth Under the Hull ?

Keep in mind that the fathometer on a charter boat may not be set to either actual depth or depth under keel. It could be set to any random depth between or even below the keel. It may be due to intent on the part of the charter company or indifference.

I have seen this before.

Only way to know is to check.
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Old 07-05-2011, 12:06   #41
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Re: True Depth or Depth Under the Hull ?

Obviously, this is a personal choice, but I had a friend who used the "under my keel" method, and his boat draws 4'. When we cruised together, he would tell me "I just saw a 2' depth"... and of course I would freak out! So, then I would remind him to tell me the water's depth and he would say "oh, I have 2' under my keel, not a depth of 2'"....

and I would go "grrrr"

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
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Old 07-05-2011, 12:54   #42
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Re: True Depth or Depth Under the Hull ?

I honestly dont care what the depth is as long as my keel is not hitting the bottom. I draw 5'8", my sounder is set to read what is under my keel...If I really want to know what the depth is I can add the 5"8" to get total depth.
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Old 07-05-2011, 16:34   #43
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Re: True Depth or Depth Under the Hull ?

Actual Depth - with a dymo label above the sounder indicating that depth is waterline depth.
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Old 07-05-2011, 18:12   #44
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Re: True Depth or Depth Under the Hull ?

Lifejacket, how far are you willing to trust the calibration on an unkown piece of equipment that any number of charterers may have diddled with? <G>

If you're going to go rockhopping, I'd suggest turning on the depthmeter while still docked, and dropping an improvised lead line over the side to give it a fast reality check.

Otherwise? If you give yourself generous clearance, no problem. If you want to try pulling a 6' draft through a 7' channel in coral...that's your option too.
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Old 08-05-2011, 04:49   #45
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Re: True Depth or Depth Under the Hull ?

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Originally Posted by Palarran View Post
If math was the deciding factor, wouldn't be just as easy to add the draft?
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)

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Originally Posted by Palarran View Post
I personally can't see where I'd be actually navigating using draft comparisons to a chart but just add it together.
It can be a useful fix line (contour) and is VERY useful in heavy fog.

Happy sailing
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