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... a logical conclusion
430 Posts
Discussion Starter · #1 · (Edited)
We spent a few idyllic days on Isla Isabel last week on our way southward from Mazatlan to Puerto Vallarta. The Mexican charts show the island only 1.5 miles out of position, and its chart rendering approximates the actual shape of the island, so it is easy to find and identify, even although the chart calls it Isla Isabela. :D

Before we left Mazatlan, I had printed an image of Isla Isabel from Google Earth, and had marked on it the latitude and longitude of a small islet in the anchorage on the island's south side.

I placed a waypoint on the chartplotter corresponding to the position of the islet, and used it as a point of reference to tie the radar overlay to the Google Earth print-out. This combination and a close eye on the depth sounder led us confidently and safely into the anchorage.

At 0745 we came to 35 metres on the Rocna in 10 metres of water about a cable off the rocks to the west, north and east of us. On the chartplotter we were 1.5 miles southeast of its interpretation of the anchorage, but exactly the correct range and bearing from the Google Earth waypoint.

Isla Isabel is a major breeding site for frigate birds, and it appears we had arrived during the mating, incubating and chick rearing time. The males inflate a bright red neck pouch to attract the females.

We spent the first day wandering through the nesting area, amazed at the tameness of the birds. The nests are in low trees, mostly less than two metres high, and we were able to walk within a metre of nesting chicks, and have their parents look on with no apparent concern.

This young frigate bird seems to be dreaming of flying away.

Isla Isabel is also a major breeding site for brown boobies and blue-footed boobies. This pale green-footed brown booby welcomed us to its nesting area on the barren windward edge of the island.

Here a brown booby chick is as unconcerned about our presence as is its green-footed mother.

The wing control sessions of basic flying training under the watchful eye of a male yellow-footed brown booby.

We left a pink-footed brown boobie watching over Sequitur.

Then we went looking for the elusive blue-footed booby, and found them on the island's east coast.

As we walked along, in many places it was difficult not to come close to the nesting boobies; there were often half a dozen and more, spaced within a metre or two of each other. The males and females take turns incubating.

Also, we had to be careful not to step on untended eggs; we saw a rather casual attitude to incubating, with the boobies stepping back to look at their egg from time-to-time, and some wandering off for a while, and then coming back. This one seems to be saying to its egg: "I know I haven't been using an egg-timer, but you must be ready by now".

We could almost hear this one saying: "OK, you kids be good, I've got to get away from this booby hatch for a bit"

The boobies seemed very friendly and inquisitive, and seemed as interested in us as we were in them.

We also spotted some red-beaked tropicbirds in the hollows of the porous lava cliffs.

There is a lot more about our experiences on Isla Isabel, and other places we have been the past five months of our cruise on Sequitur's blog

... a logical conclusion
430 Posts
Discussion Starter · #4 ·
Great stuff, Michael

Please keep an eye out for a Passport 40 out of Vancouver, called Naida. Say hello to Barb and John if you have the time.. great folks. There are in the general area now.
We'll keep our eyes peeled, but bear in mind there are many dozens of Canadian flagged sailboats here, and finding them without further information would be a tad serendipitous. We'll say hi for you. :D

... a logical conclusion
430 Posts
Discussion Starter · #13 ·
Beautiful! I am curious about where you think the error was? 1.5 miles is a long way off when 10 meters is considered satisfactory for a GPS. Do you think it was the Mexioan charts (many older charts are not accurate), the chartplotter or Goggle Earth? I am asking because there have been reports of grossly inaccurate position date from GPS.
The Mexican charts are notoriously inaccurate. We commonly found uncharted islands, misplaced islands, charted islands that didn't exist, points, rocks and shoals way out of position and many very crude representations of coastlines. In our blog we have often commented on this, sometimes with illustrations, such as: Bahia Concepcion, Baja

Paper charts and chart plotter renderings of the Mexican coast are to be used as rough guides only. To navigate safely there, it is essential that you not trust them, but rely instead on the basics: your eyes, your depth sounder and your common sense. The radar helps jig the chart to the GPS, but from there you use the chart as only a very old, rough sketch.

Sequitur is now in Patagonia, and we have been finding the charts of the Chilean coast very accurate.
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