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stevemac00 06-12-2010 07:59 AM

Reading Charts
 
I switched from NOAA ENC to Navionics and I'm confused on the little subscript depths. The software units are set to feet. It seems absurd they can be inches or fractional feet. I might think fractional fathoms but again, we're in feet as you can see around Sandy Cay in the Bahamas. So, what is going on?
http://i208.photobucket.com/albums/b...ac00/chart.png

sailingdog 06-12-2010 08:37 AM

Those are in decimal feet IIRC. The subscript is how many tenths of a foot deep it is...

stevemac00 06-12-2010 08:48 AM

Thanks dog. That's what it appeared to be but I had difficulty imagining that kind of resolution - especially in deeper water. You can see a 78.7 there.

Boasun 06-12-2010 08:59 AM

Quote:

Originally Posted by stevemac00 (Post 612376)
I switched from NOAA ENC to Navionics and I'm confused on the little subscript depths. The software units are set to feet. It seems absurd they can be inches or fractional feet. I might think fractional fathoms but again, we're in feet as you can see around Sandy Cay in the Bahamas. So, what is going on?
http://i208.photobucket.com/albums/b...ac00/chart.png

Actually those charts are in METERS. Not fathoms & feet.
So if you are using charts that the depths are in Meters you will need to change your depthfinder to meters and know the draft of your vessel in meters.
Charts pending on the country are either in Metric or Fathoms/feet. And you need to be aware of which it is and think in those measurements.

sailingdog 06-12-2010 09:11 AM

I'd point out that using decimal feet to indicate depths is less than useful and more wishful thinking than anything else. Given all the variables involved in bottom sounding, water level, tides, and such, the idea that 1.2" of distance is actually measurable in any significant way is just ridiculous.

sailingdog 06-12-2010 09:14 AM

Boasun—

i don't think so, given the depths on the NOAA ENC charts I have for the same area. If those are meters or fathoms, then the depths of the ENC charts are off by a factor of 3 or 6... which I tend to doubt.

http://adriftatsea.com/files/sandycay.png


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