The Boat Timer app works out corrected times for any rating system. But not all rating systems use the same method to do the calculation, so a club in New Zealand using the Weymouth system got in touch to ask if it could be used with Boat Timer.
The Weymouth rating numbers are ratios, so a Laser has a Weymouth number of 0.91 and a slower boat such as a Laser 4.7 has a Weymouth number of 0.87. This makes calculating a corrected time simple as you can multiply the Weymouth number by the time the boat took to complete the race to get a corrected time.
As Boat Timer uses a different method based on UK ratings systems to calculate the corrected time, the Weymouth number has to be converted. Fortunately this is not hard; dividing 1000 by the Weymouth number gives you a rating number that works in the app.
But why 1000?
UK Rating Numbers
In the UK, most races use the Portsmouth Yardstick (PY) though there are others in use; the Great Lakes system for example. These two use a baseline of 1000, by which I mean boats are given a number that is above 1000 for slower boats and below 1000 for faster ones and that number is used to calculate a change to the boat’s finish time.
The formula for these baseline 1000 systems is:
e / r * 1000 = c
e is elapsed time in seconds (the time a boat took to complete the race)
r is the rating number
c is the corrected time in seconds (the time you use for scoring the race)
American Rating Numbers
In the USA, the US Sailing D-PN system was based on the UK PY system but modified for their own racing conditions and classes. It is a baseline 100 system so rating numbers typically range from 80 for a fast boat to 120 for a slow one. Interestingly the USA system has the option of using different ratings for different wind strengths. It is fair to say some types of boat are better in lighter winds and some better in stronger, so the D-PN table has a general D-PN number similar to PY but also has D-PN1, D-PN2 D-PN3 and D-PN4 for the different wind strengths. So you can choose whether to use the all-weather number or go for a fairer number for the race conditions.
As Boat Timer assumes a baseline 1000 system and D-PN is a baseline 100 system, using a D-PN number in Boat Timer requires converting it by multiplying the D-PN rating by 10.
Creating Rating Systems In Boat Timer
At present, Boat Timer has the PY and Great Lakes rating systems in the app, though more will be added in the future. But it is possible to add your own system.
In the Options – Classes menu you can open a class document (for example, the Laser class) like this:
To add a new system, fill in the name of the system (eg. Weymouth or D-PN) in the New Rating Type box, add the Laser number in the Rating Value box and press the Update Class button.
When you open other classes, you will see the new system in the options for Rating Type. Initially, any class you have not edited will have a rating value of 1000 so it is necessary to add values for the classes in your races. Don’t forget to convert the rating number to a value that works in Boat Timer.
And finally in your race, select the new Rating System for each start and your rating system will be used to produce results on corrected time: