We showed in our previous GeoGarage blog article that the grounding of the Vestas had no relationship with some positional discrepancy in the nautical charts, contrary to a similar grounding such as the USS Guardian in the Tubbataha reefs (Philippines) which occurred last year (see GeoGarage blog)
A spokesman for the Volvo Ocean race said that it would be reasonable to assume a large reef formation would be easily detected early on and avoided by changing course as 4 other boats did before Vestas grounding but during the day time not in the darkness.
(Joint Typhoon Warning Center)
MTOTEC) 29-11-2014 09:00Z
“Wouter’s reply was that the depths went from 3000m to 40m, (which) were the extremes of the depths, the current was negligible and we would monitor the wave state as we approached...”
“In hindsight we would’ve continued to zoom in on the area much more, on the electronic charts. Not doing so is the big mistake that I made, but the good thing is that we didn’t make any more.”
Racing navigation isn't ordinary navigation.
Before they left Cape Town in 40 knots of wind, the teams had already been warned of a possible cyclone. They then skirted an iceberg exclusion zone in the Southern Ocean, dodged a tropical depression and had to keep clear of a new Indian Ocean exclusion zone (released one day before the start of the leg) in case of pirates, which lead to set the Cargados shoas in the direction of the Abu Dhabi final destination.
Note that an independent report into the grounding of Team Vestas Wind's boat has been set up by the Volvo Ocean race.
David Burch in his own blog writes some interesting articles 'How a big, well-run, high-tech race boat, can go aground... almost' & 'Don't blame eCharts for anything' completing our first article.
showing a continuous vision of the Cargados Carajos shoals,
with 'exaggerated' shallow (land) parts on zoomed out views
Other example : same continuous vision of raster charts zooming from general to detail
with British Admiralty charts :
see zooming animation on the Marine GeoGarage with UKHO raster charts layer
- GB104702 Indian Ocean - Seychelles group to Nazareth Bank and Agalega Islands (overview) scale 1:3,500,000 (updated 31-05-2012)
- FR274880 Ile de la Reunion to Rodrigues island and Ile Tromelin (general) scale 1:1,700,000 (updated 21-03-2014)
- IN42503A Cargados Carajos shoals (approach) scale 1:45,000 (updated 25-03-2014)
showing that the shoals are not correctly displayed on one of the chart levels.
Note : the same behavior occurs on other commercial nautical vector charts : Navionics / Transas
showing at high scale depth soundings (on the South East part of the shoals)
whose source are probably coming from the Indian official IN42503A ENC
These above behaviors -with commercial electronic charts- underlines the issues in matter of cartographic generalization of vector-based data especially with computer automation.
Extract from NOAA document (1988) :
All charts are reductions of some part of the environment.
The reduction of the environment to a more comprehensible scale concomitantly yields a variety of undesirable consequences.
- a decrease in the distances separating features on the chart;
- a loss of visual clarity due to overcrowding; and
- a shift of visual importance from the specific to the general.
Also, entire features might have to be eliminated, enlarged, combined, and or displaced to fit within the graphic constraints of a typical chart.
To this end, the cartographer must apply a series of manipulations to the chart data in order to depict the important information at the reduced chart scale.
showing how the chart accuracy and display of a coastal area
will be varied related to the selected scale range.
The establishment of rigid guidelines for generalization has heretofore been a cartographic enigma.
Well known cartographic expert M. Eckert (1921) considered cartographic generalization as an subjective process dependable only on cartographers skill.
Today with the some advanced computer aid tools, automated algorithms are used to help the cartographer in the generalization processes especially for the coastline and bathymetry (soundings and isobaths).
The ENC data creation is the process to design and plan an ENC database, taking into account digital generalization factors.
Multiple representation of ENC data is controlled by SCAMIN attributes in the s-57 norm.
The SCAMIN (abbreviation of Scale Minimum) value of an object determines the display scale below which the object is no longer visible on an ECDIS, in order to reduce the amount of clutter displayed and to assign priority to the display of the different objects.
e.g SOUNDG objects -depth soundings- with SCAMIN=10,000 are not be displayed when viewed at smaller scales (>10,000)
So when presented in shipboard compatible Electronic Chart Systems (ECS) or Electronic Chart Display and Information Systems (ECDIS), the user can zoom in to the ENC and be presented with an increasing number of features, which only become visible once an assigned scaling minimum is reached, the SCAMIN s-57 attribut.
Note that in the next version of the ENC norm (s-101), an ENC should ideally be displayed between two scales: Minimum Display Scale and Maximum Display Scale. (see IHO)
But some spatial objects in the usual s-57 norm such as natural coastlines (COALNE) may not be included within SCAMIN.
For example, a lower scale coastline is a generalized version of a higher scale coastline achieved by automated line simplification and smoothing techniques.
Following to some Email discussion with Nick White (navigator and Expedition software developer), it must be remembered that the 3 navigation software used in the Volvo Ocean Race (Expedition, Adrena or B&G Deckman for Windows) are ECS dedicated at first to weather routing, each using commercial electronic charts (C-Map MAX in this case, but are not compatible with raster ARCS from UKHO) and not ECDIS systems (with ENC charts) fulfilling the requirement under SOLAS regulation so they can not be used to replace official paper nautical charts which are available onboard (Use of private produced charts is not officially approved for navigation).
As ECS are at first dedicated to routing (weather optimization function for racing and performance), so usually displayed at low scale charts and are not really related to navigation as such : they might be only used as additional navigation aids to complement the usual job with the paper maps.
But it's also true that today, modern race boats have rudimentary room for A0 paper charts : so it's not obvious to always get all the relevant charts accessible on the chart table.
GSHHS World Vector Shorelines file (WVS) in black spots (general & detailed) + the one from Google in yellow
By the way, routing software on the markets offer the possibility to launch routing calculations with land avoidance for a performance point of view, so really used for large land masses as sailing can be done quite close to land/reefs.
Generally, the land avoidance routing algorithm uses high resolution shoreline files in order to check the route does not cross the land, or any shallow areas (via depth/hazard avoidance).
see zoom in the South of the Cargados
(courtesy of Volodia)
In conclusion, it's quite common nowadays -especially with the newer generation of sailors using electronics as a primary means of navigation-, to see that all these charting systems (plotters, software and mobile applications) lull people into an excessive sense of security, with the risk of encouraging them to rely too much on these tools they have come to trust, but which can't be the only key for safety of life at sea.
- NOAA : Behind the accuracy of electronic charts--What every mariner should know about electronic and paper charts / Differences Between RNCs and ENCs
- NGA : Electronic charts
- ESRI : MapGen (1996)
- Cartographic generalization and contributions to its automation
- Specifying requirements for automatic generalization of ENC
- Panbo : Lessons of Vestas Volvo wreck but what about the C-Map grounding alarm similar
- Vimeo : Team Vestas Wind skipper Chris Nicholson and Sailing Anarchy's Alan Block after shipwreck - First video interview