Dodging the Thin Spots

The US Army Corps of Engineers constantly surveys channels and inlets and after validating data, may publish depth surveys and waypoints long before they reach the NOS for chart inclusion and distribution. If you have a laptop and a charting program that allows you to load images and calibrate them as “charts” you can take advantage of this early data.

Usually the Corps (USACE) data is made available via pdf. If your chart program can upload a pdf as an image. Skip down.

If not, convert the pdf file to the image type specified by your charting program. Most expect files with a minimum of 256 colors. So select that or more when creating the image. There are several freeware programs which allow this.

Now follow the charting program instructions for upload and calibration. Most allow waypoints to be used for calibration. The USACE usually provides these in the pdf. They are usually in the DD-MM.mmmm format. Most programs will look for DD.dddddd input, but hey, you know how to input waypoints.

Once the chart is calibrated it will be saved in the proprietary format used by the software. From then on it can be treated as a chart. It will quilt, zoom, look-up just like any other chart.

As you might expect, the USACE is using survey quality GPS. so you if you don’t have WAAS or DGPS modes you might want to buy a “puck” style GPS just to get those modes for the tight spots.

Clearly this is handy on the AICW. But it can also be important if there has been a sinking in or near an inlet and the USACE has plotted safe passage.

One particular advantage of this method is color depth information grading from blue is best to red is rotten.

For preparing to transit a difficult area I have also loaded the USACE images as “overlays” in Google Earth to get a sense of what I should be seeing on the various legs.

For my global friends, I will continue to research similar sources on other shores, but so far I have come up dry.

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