Stuart Cresswell wrote in message ...
The message
from (Joakim Majander) contains these words:
I've been trying to find some information about the accuracy of the
time allowances in a IMS certificate.
All handicaps are spot on accurate - you accept that when you are rated
and when you enter a race under the appropriate conditions.
My objective was not to complain about ratings. I just would like to
know how close they typically are to real life. If you are going 0,5
knots slower than you "should", you would like to know is that due to
poor sailing, poor trim of mast etc or is it just an normal variation
in IMS VPP.
I know that it may be possible to say that in a particular condition
your boat is faster/slower than the rating you have... but I say again
you accept the rating when you enter an event under those conditions.
Everybody seems to know that, but I would like to see some figures.
Remember that unlike other rating systems, IMS is able to take into
account different wind directions and speeds.
It is your objective to sail round the course more faster than your
ratings than the other competitors (or less slower) regardless of the
accuracy of the ratings.
Of course. Does this mean it is useless to discuss the accuracy of
ratings???
What may be of interest is that is a rating results in a TCF
corrected/rounded to three decimal places then a change of 1 in the
lowest place requires the boat to be 3.6 seconds faster for each
corrected hour that she sails. In other words if two boats have
corrected times less than 3.6 seconds/corrected hour apart (eg 18
seconds for a five hour race or 259.2 seconds for a 72 hour race) then
if the TCF of the slower (on corrected time) boat was incorrect by 1 too
low in the last decimal place she should have won.
I a agree, that 3 or even 2 decimals on a time-on-time rating is very
accurate. In my example we were slower on the last legs by 40
sec/mile. This would transate to ~250 seconds (= half a mile) in an
hour in those conditions. On a time-on-time correction (which IMS is
not), this would be a disprepancy of 7%.
Joakim