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Routing 6 of 7 : A Chart by any other name...

Most sailors are well aware of the difference between Raster and Vector charts. I have access to both on board plus of course real paper – albeit gradually getting out of date 🙁 I think we are all past having long debates about which format is better. You will probably have huge amounts of storage on your laptop or various USB drives – so long as you archive and backup all those terribly interesting digital photos and videos!.

If you are like me you will just download and store all the charts that you can get your hands on for the waters that you sail. If you are in N American waters then the process is easy. At the very least you can just download the free (vector)  NOAA ENCs charts – latest edition notices for paper charts are here

NOAA Raster Navigational Charts® (NOAA RNCs) are full-color digital images of NOAA’s entire suite of paper charts. NOAA provides weekly updates to the RNCs, which are available for free. NOAA RNCs are official data that can be used in many types of electronic charting systems, including Raster Chart Display Systems (RCDS) and Electronic Chart Display and Information Systems (ECDIS)

Vector charts are more suitable for manipulation by software programs attempting to calculate optimal routing – especially if it comes to manipulating stored data about obstacles; charted dangers or merging charted data with data that you yourself may have stored using the PBG type functionality.


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Routing 5 of 7 : Algorithms

At last we come to the heart of the issue at hand, the optimal routing algorithm.

This is where the software must now manipulate:

  • The planning criteria such as waypoints, arrival time, departure times and so on
  • Real time instrument data, and any fine tuning parameters stored by the user eg. True wind adjustments
  • Boat characteristics and polars either general or specific to the boat
  • Tidal stream data both general from charts and specific based on local knowledge or higher quality data from the supplier
  • Weather data both actual and forecast
  • Collision avoidance such as AIS, MARPA, charted obstacles, user defined areas.

Not to mention the job of outputing data to instruments and to the user via a suitable user interface that makes understanding as well as user response easy and relevant.

Quite a feat of programming !


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Routing 4 of 7 : Boat characteristics & learning to Wally!

This is part 4 of the quest for the best optimal routing calculations within ECS/ECDIS systems today. In this posting I wanted to consider the use of polar diagrams and data that represents the performance of the boat in a variety of wind conditions.

Catalina30-Polar Of course wind cannot be taken in isolation when comparing your actual boat performance against any given polar diagram. The manufacturers polar diagram will tend to be an idealised version of what your boat will do at its design weight and under good sea conditions. The most likely source of polar table information is a velocity prediction program, or VPP: a computer program that uses information about the boat’s design—the hull lines, rig plan and so forth—to predict the yacht’s performance.

The image to the left for example, shows a pretty good polar diagram supplied for a Catalina 30 – and here you can see it notes that this was with a 150% genoa and the boat had a folding propeller.

Software designers sometimes incorporate other factors at this stage that will either automatically or manually take into account wave height, and other boat performance characteristics such as surfing down large waves for example. For a glimpse of the maths involved in calculating polar diagrams have a glance at this presentation from Pau Herrero, Luc Jaulin, Josep Vehi, & Miguel A. Sainz


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Routing 3 of 7: Data Inputs (wind, pressure, tide, streams, wave heights etc..)

There is a famous saying with computer software GIGO – garbage in garbage out.

So this review of software based routing calculations starts with the data that is being input.

There are 5 main sources of “data”:

  1. The expert assessments and factors stored in the software by the authors, and their expert consultants such as Michel Desjoyeaux
  2. The instruments on the boat itself feeding data in real – time
  3. The behaviour of the boat – its specific sailing characteristics – especially as represented by a polar diagram(s)
  4. The adjustments made by the skipper/navigator based on experience, or experiment.
  5. Data from external sources especially GRIB data.

It is this GRIB data that I will look at first.


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Routing 2b of 7 : Routing planning and optimisation an extra brain as well as a pair of hands...

In my previous posting I listed those systems which were clearly aimed at the racing sailor. This is not meant to be a drawback – it depends what your objectives are as a sailor as well as your capability and skill level. They very accomplished pieces of software and provide at the very least a source of information to the cruising sailor about the higher art of race tactics, tuning and performance.

The next group are NOT inferior to the the first (TableA) in any way –  but I feel that they are less likely to be underutilised by the normal cruising sailor than the ones in the racing stable above. I feel that they may be operated in more of an amateur manner with less fine tuning than the top racing packages. This is a backhanded complmemnt to SeaPro and MaxSea – systems which are very well accomplished on the racing circuit !

It may seem strange to put MaxSea in this table since there are dozens of race wins attributed to it… but it is included as testament to the ease of use of its interface that I believe makes it more intuitive than the race packages above. It is truly a race class piece of software but it can easily be used by a cruising sailor with its elegant “TimeZero” interface.


Routing 2b of 7 : Routing planning and optimisation an extra brain as well as a pair of hands… → Click here to continue reading →

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