The default IMS rating you are referring to is the General
Performance Handicap (GPH) which is one of the various "Simplified
Scoring Options" that can be used in IMS. They can be found at the
bottom left of the IMS certificate. They are all based on the GPH
and International Level Class (ILC) ratings.
Basically, the ILC rating is for use on normal races and the GPH is
for offshore races.
Just to clarify, here are a couple of excerpts from the Ocean Racing
Club (ORC) minutes:
ORC Annual General Meeting -
"...the Inshore handicap, which is based on ILC with no wind
averaging, should be used for short, inshore races. GPH, which
incorporates the existing wind-averaging spread suitable for long
races, should be used for the scoring of offshore races only, and not
IMS International Technical Committee (ITC) -
"The ITC recommends promoting the use of the ILC average when typical
day races are scored with a single number, although advises that GPH
remains suitable for coastal or offshore races without a predominance
of beating or with unpredictable wind direction."
The simplified scoring options can be used for TOD and TOT so are
extremely easy to use with Sailwave.
The ultimate level of IMS race scoring is to use Performance Curve
Scoring. At this stage, to use this you have to use the ORC's race
scoring package, Altura which is available for the ORC's website:
Basically, you can construct a course based on the true wind angles
and the windspeed. The software then uses the predicted time
allowances from the IMS certificate to calculate a Performance Curve
for each boat.
This Performance Curve is your boat's "rating" for this particular
Doing this is a bit of a pain and, in response to this, the ORC put
some constructed courses on the IMS certificate to simplify the
The various types of constructed courses given on the certificate are
Wnd/Lwd VMG: Equal legs of optimum beat and optimum run.
Olympic 6-leg: Three legs optimum beat, one leg optimum run, and two
legs reaching 135 degree true wind angle. Each reaching leg is 0.707
times the length of the beat and run legs, which are of equal length.
Circular Rndm: Circular Random, as though a boat circumnavigated a
circular island with wind from a constant direction. Appropriate for
many closed-course races.
Non-Spinnaker: Circular random as above but calculated without the
use of a spinnaker. For use only in races in which the following
restrictions apply to all yachts: a) setting of a spinnaker is
prohibited, b) the entire luff of any jib is attached to the
forestay, c) the clew of the jib may be poled out opposite the boom
only with the yacht's rated spinnaker pole, d) an inner staysail is
permitted and e) a mizzen staysail for which the yacht is rated is
Ocean for PCS: A composite course, the content of which varies
progressively with true wind velocity from 30% Windward/Leeward, 70%
Circular Random at 6 knots to 100% Circular Random at 12 knots and
20% Circular Random, 80% reach at 20 knots. It is intended for use
only with Performance Curve or Performance Line Scoring.
So where does that leave Sailwave?
Well, as Colin rightly pointed out, it can be used TOD and TOT with
the GPH and ILC given on the IMS certiciate. (Don't you just hate
I really can't see Sailwave as being the place where you enter all
the IMS time allowance data.
What might be possible is to get the Performance Curve into
Sailwave. For example, on the Olympic course, there will be a
Performance Curve for each boat. Note that this will depend on the
course leg lengths and conditions on that particular day.
What would be good is if the ORC was a bit more forthcoming about how
it interpolates these Performance Curves from the constructed course
data. Given that information, the actual scoring of a race is
Colin: I've sent seperately an Excel spreadsheet that explains this
in a bit more detail for a particular race, using the "Ocean for PCS"
Anyway, I hope this clears things up a bit.
Ocean Racing Club of Victoria
NB: Do you mean full IMS or default rating IMS or something
there seems to be N ways in which the IMS data can be used. You
default rating IMS in Sailwave now using the custom rating system
(since it only involves one parameter). I'll also add Americap
--- In email@example.com, "Colin Jenkins" <colin@s...> wrote:
seems to be a simplified IMS-ish-thing.