Wolstenholme Models for Portsmouth Numbers

Handicap Models Supplementary Note 8 April 2013

1. The models I am currently using are shown in Model Note 130408
   
2. The practice of using a separate formula for bilge keel boats is likely to continue. A satisfactory way of combining fin and bilge in one formula is so far elusive.
   More work will be done to develop the bilge formula based on expanding the base data with as much reliable information as possible. The current model does actually work quite well but I am not satisfied that it is sufficiently robust as yet.
   
3. In terms of model development in general, I am waiting to some extent on the general reaction to the RYA’s NHC system. I have already done some analysis of their figures and I am not impressed. Plus, I believe the process of ‘correcting’ after each race to be cumbersome, often inappropriate and subject to manipulation. Someone described it to me as a ‘drive towards mediocrity’. All of this aside, what is of fundamental interest is whether clubs will want to stick with a time correction factor of PN form, i.e. a divisor, or would prefer a multiplier form, as in the NHC (and others). From a modelling point of view, a multiplier is a better structure than a divisor. If there is a general desire to move to multiplier form, I will produce models for it.
   
4. One thing I am looking at this year are the adjustments. For engine propeller type, we have so far stuck to the RYA former guidelines. However, there is a view that a 1% difference between IBF and IB2 is too little, that the effect of replacing IB2 by IBF is more significant. Most of the ESSC fin-keelers are IBF these days and I am thinking of adjusting the formula to make IBF the ‘standard’, then adjusting for IB2 etc. We will keep the numbers for IBF boats as they are now and those with IB2 would get a more generous handicap number. I am thinking of 2% relative to IBF. I will experiment with this over the season.
   
5. At ESSC, the handicaps for the season are described as HN = FN + CA. FN is the ‘base’ handicap derived from the formula. CA is a ‘club adjustment’. CA is partly a personal handicap based on the previous season’s results in order to make it a little harder for the last year’s ‘winners’. CA might also be used to allow for such things as someone getting used to a new boat, or for some reason a feeling that the formula is slightly under or over generous.
   
6. All formulae assume a downwind sail capability. In the interests of simplicity, details of spinnakers, chutes etc are not included in the formulae. For certain of our races which are known to be predominantly downwind, a handicap number is adjusted by +4% if a boat does not use a downwind sail.
   
7. Some clubs may wish to adjust their numbers for factors not included in my model specifications, e.g. age of boat, age of sails, boat construction – these are all a matter of local judgement. It is recommended that most adjustments be done on a percentage multiplier basis, as for those shown in my notes.
   

Linda Wolstenholme