Beginner Chart Reading Question

zboss · #1 (**permalink**) 03-24-2011

Folks,

I have a basic question regarding depths on paper charts.

My maptech paper charts sound in meters. However, on some readings there is a small number down and to the right of the the sounding.

I have no idea what that number is... I have searched chart 1 for that information but I cannot find a clear reference to it. The numbers will vary greatly even if the depth remains the same between two points.

I was suspecting that they were alternative soundings but I want to make sure. So - what are they?

- z

jackdale · #2 (**permalink**) 03-24-2011

Quote:

Originally Posted by zboss

Folks,

I have a basic question regarding depths on paper charts.

My maptech paper charts sound in meters. However, on some readings there is a small number down and to the right of the the sounding.

I have no idea what that number is... I have searched chart 1 for that information but I cannot find a clear reference to it. The numbers will vary greatly even if the depth remains the same between two points.

I was suspecting that they were alternative soundings but I want to make sure. So - what are they?

- z

That would be 10ths of a meter.

zboss · #3 (**permalink**) 03-24-2011

Quote:

Originally Posted by jackdale

That would be 10ths of a meter.

OK! so... 15 with a little 2 next to it means 15.2 meters/49.8 feet.

Thanks.

TQA · #4 (**permalink**) 03-24-2011

This is something to be REAL careful with when you switch charts and pilots.

Some give the depth in metres some in fathoms with the small numbers being feet and some in feet.

Something I triple check always.

jackdale · #5 (**permalink**) 03-24-2011

An easy check: if the small number is larger than 5, it is probably metric.

Always read the title block of a chart. It has essential information.

Even though Canadian charts are usually metric, we still have some that are in fathoms and feet.

capttb · #6 (**permalink**) 03-24-2011

They are making charts with the metric system in the US now? Drat! Anyone know how many meters in a fathom ?

jackdale · #7 (**permalink**) 03-24-2011

Quote:

Originally Posted by capttb

They are making charts with the metric system in the US now? Drat! Anyone know how many meters in a fathom ?

2 meter = 1 fathom approximately

or more precisely 1 fathom = 1.8288 meters

knuterikt · #8 (**permalink**) 03-25-2011

Quote:

Originally Posted by capttb

They are making charts with the metric system in the US now? Drat! Anyone know how many meters in a fathom ?

If you use digital charts you set the unit of measure on the chart plotter (I can on my Furuno at least

jackdale · #9 (**permalink**) 03-25-2011

Quote:

Originally Posted by knuterikt

If you use digital charts you set the unit of measure on the chart plotter (I can on my Furuno at least

The OP is using paper charts. The depth can be set on vector charts, but not on raster charts. Some of my Canadian rasters are in fathoms and feet, but the vast majority are metric.