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Post by Canucks on Jul 18, 2008 20:55:12 GMT -8
I have a question about the markings on the depth charts. Are they in metres or feet? I am tracking some ships on Siitech and I am a bit confused. The depth at Race point is 7 but the draught of the boat is 8.3 m. I hope you can bear with me because I am really confused.
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Nick
Voyager
Chief Engineer - Queen of Richmond
Posts: 2,078
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Post by Nick on Jul 18, 2008 21:12:19 GMT -8
DENelson might be able to answer this better, but I'll try.
You can get charts in a variety of measurements. While metric is one of the most common, it could be that the charts on Siitech are in fathoms. One fathom is equal to 6 feet, so in your case, 7 fathoms would be 42 feet. 8.3m is about 27 feet, so that scenario seems plausible to me.
This is my take on it.
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Post by Canucks on Jul 18, 2008 21:14:25 GMT -8
Thanks for clearing that up Nick. Just to be clear the draught is how much the hull is under the water.
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Nick
Voyager
Chief Engineer - Queen of Richmond
Posts: 2,078
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Post by Nick on Jul 18, 2008 21:15:31 GMT -8
yes, the depth from waterline to keel.
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Post by DENelson83 on Jul 19, 2008 15:23:20 GMT -8
Where's Race Point?
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Post by Canucks on Jul 19, 2008 17:12:52 GMT -8
Race Point is just before Seymour Narrows. It is on Vancouver Island and there is a road going around it called Race Point Road.
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Post by DENelson83 on Jul 19, 2008 18:40:24 GMT -8
Here's the E-chart around Race Point.
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Post by Canucks on Jul 19, 2008 18:56:22 GMT -8
The chart on Siitech is showing that the area around race point is 7.3 fathoms which is 13m. Which one is more accurate E-chart or BSB charts?
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Post by DENelson83 on Jul 19, 2008 19:01:49 GMT -8
Whenever you see a depth at a point on a chart, that's known as a "spot sounding," which means the water is that deep only at that one infinitely small point.
The chart that Siitech is using in that area is CHS chart 3001.
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Post by Canucks on Jul 19, 2008 19:02:29 GMT -8
I'm not sure what that means but there is a dark blue circle that says 7.3.
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Post by DENelson83 on Jul 19, 2008 19:05:19 GMT -8
The dark blue on chart 3001 means that the water is less than 10 fathoms or 18 metres deep, and the 73 means that just one point in that area has been measured to be 7.5 fathoms deep.
The accuracy of a chart is affected by its scale. The smaller the scale, the more detailed and accurate the chart.
By scrolling the Siitech map northeast, I get the following text which is printed on the upper-right corner of chart 3001, which I believe answers the OP's question:
"DEPTHS are in fathoms and feet and are reduced to Chart Datum(Lowest Normal Tide)."
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