Using BWR to Route the Shetland – Lerwick to Bergen Race

While testing the course file before making it available here on the 2012 Races page, I ran into a curious situation with the routing parameters.

Basically, if you try to route the whole race as one route, you need to set grid size at about 2nm (and a corresponding max dist.). But because the first leg is so short, that results in routing error ‘Unable to reach endpoint’. This happens because BWR cannot create a routing tree using a grid of 2nm and actually hit the first mark – it needs a smaller grid size.

One possible solution is to just delete the mark and route from start to finish, but that makes it possible for BWR to optimise a route that sails North of the island between start and finish (depending on the wind of course), but the mark forces us to sail South of the island for the actual race.

So the best solution is to split the route up into 2, one for each leg of the race and specify smaller routing parameter values for leg 1 – which is what I have done, and what you will find in the race file posted here.

Leg 1 being so short, a very high resolution grid is possible for it (grid=0.25/max=2.0).

Note: As it is not possible to accutately predict when you will start leg 2 (and many will round at different times anyway), for the start time I have used the ‘@now’ time specifier (which means ‘Whenever you start the optimisation’ for those who ore not aware of this feature) – which will work ok if you optimise just as you round the mark – but you may want to enter a specific time – for example you know you are going to round the mark in 5 minutes, so you set the Leg 2 start time to be 5 minutes in the future.

For this reason, I chose to ‘split’ the 2 legs approximately along the ‘scoring line’ – the line extending from the mark where scores your rounding.

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