Thursday, February 24, 2011

Navigating in Mexican waters (David)

In US waters we trust the charts, both paper and electronic. With the help of GPS plotters, you know your position within a few feet. In Mexico, however, many of the charts, generated from survey data taken in the 19th century, are off by one or two miles! For example, it is disconcerting (to say the least) to find Isla Isabela more than a mile to the south east of its charted position. Furthermore, the electronic charts, at least those supplied by Nobeltec, show no detail whatsoever. 

While in La Paz, we met Bill Stockton on board True Love, a beautiful Waterline 53. Bill has written a program called ChartAid that captures a Google Earth photo of any location you choose and geo-references it to the chart on the Nobeltec screen, thus placing the photo in exactly the correct position and scale on the display. One can zoom in to whatever resolution is available from Google Earth. Wow -- what a difference this makes to navigating in Mexico! I can thoroughly recommend this $99 program.

This Nobeltec screen shot shows the charted position of Isla Isabela, compared with the actual position shown by the Google Earth photo.

Zooming in for more detail, you can even see the fishermen's shacks on the beach (click on the photo for an enlarged view).

Mystic is anchored just south of the rocks on the east side. Although the south bight is more protected, it has a reputation as an 'anchor-eater' because of underwater boulders.