Monday, February 17, 2014

IRC time versus distance handicap correction

Time handicap correction
Lets consider two sailing boats A and B. We assume that they both sail at the same speed of 6 knots.
Under IRC A rates better (0.900) then B (1.100). The race course is 10nm, the results will look like this:
A elapsed time is 10 / 6 * 3600 = 6000 seconds * 0.900 = 5400 seconds corrected
B elapsed time is 10/6 * 3600 = 6000 seconds * 1.100 = 6600 seconds corrected
A wins over B as expected.

Distance handicap correction (Flexboy)
A and B sail now a Flex race. A is set to sail 0.900 * 10 Nm = 9 Nm, B is set to sail 1.100 * 10 Nm = 11 nm.
A elapsed time is 9 Nm / 6 Knots * 3600 = 5400 seconds.
B elapsed time is 11 Nm / 6 Knots * 3600 = 6600 seconds.
Again A wins and we herewith prove that distance correction is equivalent to time correction using TCC in both case as correction factor.

Flexboy has the advantage of having all the boats sailing at the same time on the race course and makes the racing more interesting as all finish together at the same time. Flexboy has the disadvantage of a less accurate mark rounding. Experience shows that the differences between boats is 20 to 50 meters navigational error arround Flexboy.
The position of all the marks on the Flex course must also be as precise as possible, the accuracy of the geographical position of the marks must be in the same order as the precision of time calculation meaning a precision of at least 1 in 3600 or half a meter over one nautical mile. 

Marc Brugger
ADCA Racing Secretary
Abu Dhabi, 17 February 2014


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