Router, race modelling software


1.  Introduction

Router is a program which uses yacht polars from a velocity prediction program VPP (in our case we use Windesign VPP) or polars developed onboard an existing design and historical weather data in the form of GRIB files to model the outcomes of races. The output data from running the program is primarily the distance sailed and the time spent sailing by the yacht in a matrix of true wind angles and true wind speeds for any given race. In short, the yacht designer, is able to take any number of candidate designs with different characteristics and race them against each other in any yacht race for which there is historical weather data.

Owen Clarke Design have been using a weather routing service since the Kingfisher program in 1999 and have used Windesign VPP to design all our Class 40 and Open 60 designs using transatlantic and round the world race modelling since that time. The weather modelling and routing were conducted by Pierre Lasnier and his company MeteoMer using their own proprietary software and weather library. It was necessary in the past to send the yacht polar files and specific courses over which one wished to model the candidate designs to MeteoMer or another specialist company who would then create the race matrix. The data file/matrix was then imported into the designer’s VPP program. Elapsed times could then be calculated for different design candidates over these specific courses using actual measured, but averaged weather data. It was also possible to create one’s own spreadsheets to evaluate sail usage for example but this was a laborious and time-consuming process.

Owen Clarke Design has invested in Router, software that was used by most teams in the last Volvo Race. We are the first design office to run Router with weather files in GRIB format which improves the speed of input and the quality of the output data from the program. A major advantage now compared to the past is that we have complete control of the race modelling process from start to finish and are no longer reliant on a third party. All the work can be carried out in-house which makes the system far more flexible and transparent.

2.  How does Router work?

For the design of a new yacht we could for example create three (typically many more in an actual project) candidate yacht designs of different waterline beams, bulb weights etc, which obviously have three different polar files of boat speed against TWS and TWA. These polars are then imported as Excel.CSV files by Router so that it knows the performance of the three different boats in different wind conditions.

For an existing yacht which was changing its mast we could create polar files in WindesignVPP for three different rig configurations, double spreader, three spreader, rotating and so on. As part of ongoing development or to target a specific event such as the Transat Anglais, TJV or a record attempt we can work with sailmakers/teams and optimise a yacht’s sail wardrobe, since different sail wardrobes will produce unique VPP files and so different results using Router.

After discussions with individual skippers regarding their sailing style sails can be selected and de-selected from the sail wardrobe at different points in a race. This is useful for events such as the Vendee in so far as we can alter the boat’s polars between the Atlantic and Southern Ocean legs thus mimicking the actions of the short-handed sailor.

We are also able to introduce a base boat VPP file that cuts in and routes all boats using the same polars for very low and very high wind speeds. This is obviously used to create a more level playing field where boats are either in ‘survival mode’ or performance has more to do with a degree of luck and local conditions rather than performance characteristics of a certain design, sailplan etc. This file can be switched on and off, the results analysed and a judgement made with respect to the results.

Router also requires access to weather data for whichever course/race the candidate yachts are being raced over. We have twenty years of data covering the route and timetable of the next Volvo Ocean Race and similarly for the Vendee Globe we have historical GRIB files dating from 1990 to 2009 for the months of October to March.

Not only is Router able to predict the ‘winning’ design/sail configuration in any virtual yacht race, if one also inputs Excel.CSV format tables of sail crossovers or ballast crossovers for instance then the output data will show for what distance and % of time any particular sail or ballast configuration is used. So, crossover data be it for sails, ballast, daggerboards or keel cant is another type of input that Router can use.

Once the external data has been set up in folders that can be read by the program there are a number of inputs required by Router itself to run correctly. The main requirement is for the designer, sometimes in consultation with the project team to create geographical boundaries to the courses that the virtual yacht will sail. These can be seen on the next page outlined in white on the sphere that represents the globe. This is a representation of Vendee Globe route model with the ITCZ near the top of the sphere where one can see that the courses are constrained at the equator. The outward and return leg course boundaries that are considered by the program along with the route around Antarctica are clearly visible.

These boundaries are defined by waypoints, turning marks or gates as published in a Notice of Race. Also land, coastline/headlands and areas or distances from the great circle that from experience the skipper might feel are ‘practical no go areas’ can be included as limits of the available routes. The narrower the boundary the less options available for routing away from the average course.

To set up the ‘right boundaries’ for a given race initially requires a number of runs to fine tune the model, in some cases allowing greater freedom and in other instances reducing the boundaries to allow the program to run quicker because it becomes obvious that candidates are not being routed in that area.

To illustrate other features of Router we will continue to use the Vendee as an example, although most of the same inputs/outputs and features apply to races such as the Fastnet, Sydney-Hobart (additional access is required to high resolution inshore weather data for races run close to the coast) as well as trans-oceanic and round the world events.

With the candidate models (defined by their polars/sail crossovers etc) ready to run, GRIB files available and the boundaries of the race course defined Router is now ready to run. For the Vendee Globe we typically select every year of weather data available and run the yachts in those years starting on the actual race start day and also for such a long race selecting race starts three days ahead and three days before. This increases the data available for averaging statistics and again helps to highlight and smooth out data where there may be anomalous weather systems over the course.

Each candidate yacht’s performance can be reviewed at any point in the virtual race by ending the course at a waypoint. Typically as we have done previously we split the Vendee Globe up into ‘legs’, in this case six. The Atlantics going south, crossing the Indian and Pacific Oceans, then from Cape Horn the two Atlantics heading north. The data produced then for a small sample Vendee Globe simulation such as might be required to look at a downwind sail program would consist of: three models, six race sectors, twenty four waypoints, and seven different start and finish dates. This creates a good deal of data which is output in the form of multiple Excel spreadsheets.

3. Output data and how is it used?

The Excel spreadsheets produced are processed and reviewed manually, summarised and then reported upon. For new boat programs the results are normally then reviewed with the client, sail makers, spar makers and other members of the team during a project meeting.

Graphic outputs can be circulated to the sailing team or reviewed real time as a reality check for courses that should be removed from the data set. For instance, although in some cases the computer might look at the polars and send the yacht on the fastest course, the sailor/navigator might never make such a selection because it would take them too close/too far away from land, rhumb line or great circle. In general what we’re looking for as designers is the ’mean average’ of conditions that a yacht/sailplan/appendage configuration is likely to hit upon in any given series of years. At the same time, without compromising the overall performance it would be usual to ensure that a yacht is not overly ‘type formed’ and that there is some leeway when faced with uncharacteristic conditions on long courses. Such anomalies can be caused by cyclic events such as El Nino, or being a day ahead or a day behind a weather system. Router picks up and displays this kind of deviation from average routes very clearly.

The previous graphic shows the fastest courses selected by Router for two different Open 60’s during a simulation of the 2004 Vendee Globe. Each yacht started on the same day and time as the actual event and for clarity so the routes can be seen we added just two additional starts, a day ahead and a day before. These graphic outputs help to provide more understanding of what is happening when reviewing data in spreadsheet format.

Elapsed time over the different elements of the course are of primary interest to everyone. However, as mentioned in the introduction, if sail crossovers or ballast tank crossovers are available then output tables such as the one below indicating the time/distance covered in various ballast tank configurations can be produced.

From this table it can be seen that this candidate Open 60 in this particular year sailed the Vendee course without ballast for @ 50% of the race in terms of time, and 40% in terms of distance. The ballast/tank configurations themselves are greyed out.

Similar outputs can be created for keel cant, sail usage and daggerboard positions as well as wind angle data that allows a port/starboard bias evaluation for any course to be made.

M1A LCB Fwd 5.5
Ballast Miles Miles-% Hours Hours-%
10713 0.41 804 0.47
651 0.02 59 0.03
996 0.04 86 0.05
364 0.01 30 0.02
1851 0.07 123 0.07
2280 0.09 126 0.07
215 0.01 9 0.01
4921 0.19 230 0.14
4401 0.17 229 0.14
Sub Total 26393 1697

4. Advantages over previous weather modelling

Having used Router for the design of OCD 175 our latest Open 60 we can clearly see among the advantages there are:

  • Rather than designers/sailors selecting a course down which to compare different designs Router selects the fastest routes from a range of courses within selected boundaries and based on the polars of the different boats. Navigators/skippers will recognise the way that Router does this in practice because it’s very similar to onboard packages such as Expedition and MaxSea.
  • The graphical interface allows the designer/sailing team to reality check the courses selected by router.
  • Anomalous runs can be filtered out or turning the approach around potential spikes outside mean weather conditions are highlighted for different years/start times.
  • Designs can be reviewed using average weather data over a narrow or wide range of years and specific years can be selected.
  • The average for mean statistical analysis is far greater since runs can be made with starts any number of days either side of a datum race start.
  • Teams can select their own ‘no go areas’ based on their experience and routes can be changed, designs/sail wardrobes re-evaluated from race to race as waypoints, starts, stopover or finish ports change.
  • File input and output times are reduced allowing more runs in a given time frame and so more statistical data is available for project teams and designers to make decisions.

5. Uses for Router

  • New and existing yachts: Hull, ballast, appendage, rig and sailplan design and to facilitate project choices in these areas for new builds and before modifications/refits.
  • New sails: Reviewing sails before they are built and optimisation of upwind/downwind sails for specific races. Also, particularly but not exclusively for short-handed boats the maximisation of crossovers between sails to improve range/overlap and so reduce number of time/effort costly sail changes.
  • Sail wardrobe damage control: Minimising performance loss due to damage to sails in classes with sail inventory maximums. What spares to take on long races (if any)?
  • Sail usage review:  Likely flying duration in long races and importance of sails if lost through damage which may influence choices of sail material, weight or construction.
  • Appendage review:   Optimisation of appendages for specific races.

6.            Higher resolution weather data and current files

For trans-oceanic and trans-global races standard resolution weather data is used because it is sufficiently accurate for the purpose and reduces processing time.

For events closer to land such as the Fastnet, Middle Sea Race and for starts/finishes of races such as the Barcelona World Race where local topography, as well as land and sea breezes have a significant effect, higher resolution files need to be used to achieve the necessary accuracy.

For events significantly affected by current such as the Sydney-Hobart race current data can also be imported into Router.

7.            Summary

Router combined with WindesignVPP is a cutting edge powerful program originally developed for the Volvo Ocean Race and now available to OCD clients for the design of new and the modification of existing racing sail boats.

For the fraction of a cost of a new sail OCD even at the most basic level (without wind tunnel or cfd derived sail force coefficients) can work with a sail-maker to review the suitability of sail designs within an existing or new wardrobe in order to improve the overall performance and help prevent the occasional ‘lemon’ sail that many programs come across during the life of a project.

Router is a performance enhancing, cost effective practical yacht design tool with a user interface that is not a black box and allows input and review from the sailor, sail maker and project team.

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