I am frequently asked questions about progressive handicapping, where the results of each race are used to update the handicaps for the next race. HalSail has two such schemes: NHC from the RYA and ECHO from Irish Sailing.
A frequent question is: "What about races where there is a major wind shift, or boats delayed due to breakages? The results are not a reliable indication of each boat's performance and should not be used to update handicaps."
That is true, but unfortunately there is no provision in either the NHC or ECHO schemes for excluding individual races from the handicap-updating procedure. The NHC algorithm does limit the handicap changes for individual boats if their corrected times are very far from the average, but the race is still included in the calculations. Details of how the calculations are done are on the HalSail website, here for NHC and here for ECHO. If you are mathematically inclined, you can click through from these links to the detailed definition of the algorithms.
If you are keen to exclude some races from the calculations there is a work around, but it is rather laborious. You need two racing classes, one with plain TCF handicaps and one with progressive handicaps (NHC or ECHO). You put all your boats into both classes and set up your main series for the plain TCF class and a tandem series for the progressive class. You use the tandem series to work out new handicaps after each race and manually transfer them to the TCF class with starting times just before the next race. If the results of any race are deemed unreliable, you exclude that race from the tandem series.