Wednesday 18th July - French Polynesian Charting; the Good News

Jon & Carol Dutton
Thu 19 Jul 2012 05:38

Wednesday 18th July –  French Polynesian Charting; the Good News

We should have mentioned this in the blog entry posted a little earlier but were prevented from so doing by innate incompetence and the incidence of a senior moment – again.

Most, if not all, pilot books we own (three covering French Polynesia) do two things:

  1. Warn you that GPS is an evil modern invention whose idealised view of the world may not be reflected in the available charting.  Hence, if you follow whither it beckons you may find you and your keel parting company on less than amicable terms.  Particular emphasis seems to be placed on the Tuomotos.
  2. Produce diagrams and/or extracts of French charts together with clear advice that these should not be used for navigation.  Quite what other function they might usefully perform is not clear.

All of that is liable to create something of a ‘Hm’ moment or two for Polynesian virgins (No; before you start, don’t go there) such as us.   Our chart-plotter uses Navionics digital charting (based on official French hydrographic authority data).  We also have access to some C-Map data and, whilst we haven’t done an extensive check of this, it appears to correlate with the Navionics charting. 

Whilst we have experienced no issues with the accuracy of our digital charting in the Marquesas (we found ourselves unable to say the same of the San Blas Islands’ data) this morning produced a very assuring revelation.  We turned on the radar and got it to paint over the chart.  The result was a purple paint precisely where it ought to be, overlying exactly the visible outline of the Kauehi atoll (and its near neighbour to the south) as depicted on the chart.  So, at least the atoll’s in the right place according to GPS which is a bit of a relief if you are navigating about at night between atolls (notwithstanding that radar is also probably a pretty good idea if you are doing that).  As for the detail within the atolls, it’s all a bit early to say.  But given the industrious way in which coral goes about attempting to frustrate the best intentions of hydrographers I guess we’d all accept that our eyeballs are the best authority once we get down to the really fine detail.

If we discover any anomalies in our further travels in French Polynesia we’ll let you know.