Chart Numbering??
Submitted by One Eyed Phil on Thu, 2011-08-11 16:45
I'm trying to read a map/chart book and the figures for the ocean have me baffled. The book "Fish Finder" must have an explanation in it but I cannot find it
I am not a boatie so have no knowledge of marine naviigation. So I had a look at some examples of charts on the net and they do not match what is in the book.
Instead of having a single number (depth I assume), they have a number with a 'subscript' number or letter.
I don't know if I can insert subscripts here but the second number or letter is one.
Eg, 4g, 62, 95 etc
Can anyone enlighten me please
Phil
Starbug
Posts: 563
Date Joined: 27/08/09
The larger number is the
The larger number is the depth in meters, the subscript is the decimal. 6 subscript 2 is 6.2m.
Leters are often used near the depth soundings but not as subscripts, to denite the bottom type. G would denote gravel, M mud.....
One Eyed Phil
Posts: 45
Date Joined: 27/01/09
Thank You
Thanks, that makes sense
just as an aside, does the 'point' mean that much? A matter of a few mm??
Curious, that's all
Phil
Have to add a problem with your response
The letter g IS subscript and i cannot find any other leters. Perhaps some other meaning in this publication???
Lucky Tim
Posts: 2536
Date Joined: 28/11/07
I think they only do the
I think they only do the decimal in soundings shallower than 10m. Doesn't mean much, those soundings are taken at the lowest astronomical tide so rarely will you ever see it at that depth. Usually chuck a few metres for tide etc on top of the sounding.
I guess if you nearly go aground then those few cm's might be very handy to have under the hull....
Lucky Tim
Posts: 2536
Date Joined: 28/11/07
send a photo mate, might be
send a photo mate, might be easier to explain
Feral
Posts: 1508
Date Joined: 01/11/06
depends on how old the chart
depends on how old the chart is ... ive got an old one here in fathoms .. and that tells me the general bottom type too .. but i cant say ive seen it on a new chart
Lucky Tim
Posts: 2536
Date Joined: 28/11/07
all charts, both metric and
all charts, both metric and imperial show bottom type eg, Co, S, M, Sh etc.