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Oct112010

## “Are we winning?

“Are we winning?”

You’re ahead, but is it enough? Mike Urwin explains how to calculate your position on the race course.

Originally printed in 2005 IRC Yearbook

Simplistically, each 0.001 of rating difference between two boats represents a corrected time difference of approximately 3.6 seconds per hour. This will however only be absolutely correct for boats rating very close to 1.000. So how can you be certain whether you are beating your rivals on the race course?

Starting with boat A rating 1.010 and boat B rating 0.995, if Boat A sails for one hour, her corrected time will be 1.010 hours which is 1:00:36 (1 hour 0 minutes 36 seconds). Boat B will beat Boat A if her corrected time is less than that. To find out what this means in terms of time, we want to find Boat B’s maximum elapsed time. To do this divide Boat A’s corrected time by Boat B’s rating - 1:0:36 / 0.995 = 1:00:54. In other words Boat B can sail for up to an extra 54 seconds before her corrected time is more than boat A's. An easier way of doing the same thing is to divide the rating of boat A by the rating of boat B – ie 1.010/0.995 = 1.015 and 1.015 hours is 1:00:54.

Notably, boats A and B have a rating difference of 0.015, thus confirming (54/15 = 3.6) the 3.6 seconds per 0.001 noted above. But if the boats are faster or slower, while the maths remains the same, the answer starts to vary from 3.6. If boat C rates 1.110 and boat D rates 1.095 (the same rating difference of 0.015 as A and B) the time difference for an hour’s racing is 1.110/1.095 = 1.0137 which is 1:00:49 – equivalent to 3.27 seconds for each 0.001.

Similarly, boat E rates 0.910 and boat F rates 0.895 (again 0.015 less). The time difference for an hour’s racing by Boat E is 0.910/0.895 = 1.0168 which is 1:01:00 – equivalent to 4.0 seconds for each 0.001.

For a given fleet of boats, this can then be dealt with by creating a table of time allowances for the fleet. The table above is the ideal way to deal with this. For occasions when you do not have this for whatever reason, another simple way of dealing with it is to divide 3.6 by your TCC. eg, 3.6/1.100 = 3.3 seconds or 3.6/0.900 = 4.0 seconds. The answer in each case will then be closer to the correct time allowance per 0.001 rating difference between your boat and a reasonably closely rated competitor. The answer will still be approximate, but rather better than just using 3.6!

Mike Urwin