VMG

Originally posted by iGRF

Originally posted by iGRF

So, are these 'polars' available for different boats, when was that one issued for the RS100? Where can I order one for the Alto and the EPS?

Then the next question (blindingly obvious even to an idiot) if there are such things, that are calculated on fact rather than anarchic fiction like club returns, why is it so difficult to have a given boat a permanent handicap calculated for it? 

Hi Graeme,

I generated that one for the 100.  To create theoretical polars you need three things:

1. The drag of the hull

2. The power from the rig

3. Other stuff

The drag of a dinghy hull is severly impacted by incorrect trim, waves etc.  I used the measured values from a towed 59er and tweaked it by crude judgement to suit the shorter, lighter 100.  

The power from the rig can be estimated using standard aero calcs, provided you have reasonable lift and drag coefficent estimates.  There are a number of ways of getting these, but getting accurate numbers requires money.

The other stuff covers things like crew weight, mast height, sail roach, daggerboard length etc, which affect the righting moment and hence power available.

So there are quite a few inputs, which you can either guess, estimate, measure or calculate.  The more precise these numbers, the better the answer.  To get numbers good enough to calculate a PY (becasue yes, you could, in theory use polars to calculate PY) would require a decent level of accuracy. Nice job though!

Having said that, PYs to 4 decimal places is overkill anyway.   