...using C-Maps...

Sounds like an incredibly powerful tool, requiring great processing speed, etc, and light-years distant from the sort of stuff most of us might be using... here's an excerpt from a post on SA that gives a hint of the complexity of this sort of tool (emphasis mine):

Navigating/Weather Routing skills with the opportunities and constraints of short-crewed offshore/ocean racing boats (particularly where wind speed and boat speed are the nearly constantly the same), simply cannot be compared with other norms people may be familiar with. By way of example:

Modern racing navigation programs like Expedition, Adrena etc are extremely powerful and sophisticated. In fact only those at the very top of the game use these programs to their full potential. At any one time a navigator may be manipulating dozens or more weather/current orientated routes including their own and those of other competitors. Overlaying this are the tactical route options that may not be weather related.

Putting aside covering competitors, a Navigators numerous route options will possible cover more than a thousand square miles for just the next 24 hours and tens of thousand of square miles beyond that. To add to the complexity these routes will all change many times a day due to onboard peer review, outside weather updates, onboard weather analysis, real time over the deck weather and observations, competitor route changes etc, This is all being done while doing around 400 - 500 mile a day!!! This offshore environment should not be confused with coastal racing where landforms and short races of say 600 mile or so reduce course options and therefore reduce workload let alone compare it with cruising navigation techniques.

As a consequence of this complex and exhausting process it is literally impossible to "zoom in" every time on a selected route and check it out for say obstructions, then drag out updated paper charts and other references to spot discrepancies which are an accepted shortfall in modern electronic charting.

To counter this problem a race navigator does as much planning as possible before leaving the dock where there is more time to make appropriate race notes and external information is readily to hand. For instance once this race is underway the internet and say Google Earth is off-limits. As Wouter attested to he followed these normal practises of pre-race planning for Leg 2 to the letter using the Sailing Instructions as issued.

In short, the navigators on these boats have a LOT going on beyond simple 'navigation'... Particularly, with the racing having turned out to be as close as it's been among the fleet, in what has essentially become a One Design Race. The guy quoted above makes a good point that had never occurred to me - that these guys are likely to be often assessing the optimal routing OF THEIR COMPETITORS, as well, in an effort to assess their next move. And in this particular instance, with the added work load of having to route around the periphery of a tropical storm that was creating a very unstable and complex weather situation... There was likely a shitload of other information and graphic display being overlaid on their charts of the Indian Ocean...

As you say, how some of the other competitors dealt with this situation will also be critical to understanding how this happened... Particularly DONGFENG, who passed incredibly close to the reef after a last minute gybe, and had the good fortune to arrive there in daylight... Hopefully, others will be candid in their debriefs in assessing their own "There but for the grace of..." moments as they approached this hazard...