Posting a series of related rating ideas and concepts, --very boring stuff, --just questioning different aspects of current rating systems, Trying to compare them in different ways from different perspective points and combine the best attributes of each of the main rating systems in use.

The basic equation uses r-Length -and r-Sail area div. by
R-weight in proportion to reflect differences in relation of one catamaran design to one another defined by these basics of design elements. Good proven base equation that is itself developmental and has been refined and improved in use.
The base equation provides approximately on average 90% to 95% of the total rating;what we are left to distinquish in rating calc is the remaining 10 % -spin non spin being the largest portion of that remainder , beam ;board;handicap and - windspeed effects making up the remainder of calc and formula added as reflecting these design and handicap features in proportion to each other .

Around this good base foundation we can build or add other features to reflect these other elements of design. A simple 2-windspeed modification-rating category allows this to occur.
2 windspeeds easily identified by all as trap or non-trap conditions. The goal being to reflect beam effects as wind increases, board effects correction, -and rated sail area configuration differences and how they change and relate to rated weight along with rated Length in the upper range .
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Additionally added in the upper windspeed range catagory .---With any rating system multiplying by elapsed time the duration or time sailed is much less in upper wind speeds to distance , so total time to make up a time handicap allowance on a slower rated boat is less.
The other movement in the upper speed range applies to proportional design speed potential increases .
Scaled differences based on average time are not directly proportional, lower speed time differences are greater to distance traveled . Speed differences are greater in rated scale to MPH or knots between the extreme ends of rating in lighter wind conditions. The difference in attempting to rate catamarans that reach speeds in the upper range of up to 25 knots ,---as compared to dingy monohull types with often total hull speed limits of 6 knots becomes apparent.
Any of us that race in mixed fleets with monohulls realize that once we on catamarans can lift a hull clear and pop out on the trap speeds increase rapidly over monohull design.- Less form drag ;wetted surface frictional drag proportions in ln light wind to higher wind conditions- ;righting moment ,-apparent wind all increase and build proportionately faster on themselves in the upper wind range , particularly apparent wind in the reaching and downwind mode.. Cat design often exceed true wind speed to one and a half times for this reason.
These design related reasons explain the non proportional increase in the upper range and narrowing of total time differences that need to be reflected in the upper windspeed rating range .;Again very differently than monohull counterparts with hull form speed limitation. av 6 .;This is why rating systems do not translate well between the types . The distinction not made in average time rating systems is that this is reflected in the total race duration time being less , which on average may hold true for monohulls , but again due to much greater proportional speed increases in the upper wind range we should see reflected not only less proportional time to cover distance incrementally to scale but also an actual narrowing of rated time due to these design features and greatly increased proportional speeds.

Slower rated boats may have either less length - being an average factor now,-more rated weight which includes av crew weight -on the wire in upper wind range ,--or less rated sail area, again requiring a reflective correction in upper wind range . ; These 3 main rating factors singularly or in any combination of them per design variation need to be adjusted proportionally in the upper wind speed category .

For the upper wind speed category a total rating number as calc for each class may be used as a correcting factor percentage added. We see Portsmouth ratings move approximately 3 to 5 in most classes incrementally though the windspeeds as listed ,-an average 4 pts in scale ;converting and -relating to 2.5% in scale rating effect.
The base rating being inverted used as correcting factor.
This will reflect a narrowing of differences in ratings in the upper wind range along with changes per beam-- boards-and other windspeed factors.
This will correct differences between spin and non spin types in the upper wind range . Estimated average would change -approx. av 1 to 2 % of total rating factor . Again we are adjusting this final 5 % from base rating in proportion from one cat design to another.

3 additions or changes proposed ---

1-The spin equation added per ISAF simplifies the system and helps reflect the spin area added in base equation with the weight factor.
Smaller area high aspect spin design is more efficient per same area, and should be added to the ISAF spin equation now added to replace the 4 pt spin and area above penalty in Tex.

2-The handicap added factor-converting Portsmouth rating as applied per handicap for older design with lesser design features. --Outlined but requiring development.

3- :The windspeed mod. factor calc.-reflecting beam, --board correction , -and rated L-rated weight-rated sail area inc. spin correction in the upper wind speed category .

A future category for lifting boards and foils may be added -factored into the upper wind speed when they become effective.

Also if required a future hull category reflecting P C and potential planning capability, also effective in the upper range may be added in the upper windspeed calc .


Added note;
Developing ideas concepts for a combination rating system --

Started down the wrong course with added spin cal to the current 4 pt. The better long-term solution is to use the alternate ISAF spin rating equation as outlined above .

Also considered an updated or new rated sail area calc -
but the current is standard accepted practice, and seems to work well.-It is good to periodically review all aspects of rating, this may be revised in the future. Again class oriented racing should be priority in catamaran events with rating class ,and an overall rating place awards added .

What is proposed is a combination system ,-still needing some development ,-but the basics outlined .
Combines elements of all 3 rating systems Texel -Isaf,-and Porthmouth --abbrev. --T I P . catamaran rating .

-The calc. as proposed would be - Tex base -remains the same -
ISAF added spin and other minor rating features added,----

Plus HAF -
Handicap Added Factor based on Porthmouth rating ,-
.-Cetainly under this proposed combination rating Porthmouth is reflected and older lesser boats through handicap do have favorable rating numbers , being added and adjusted much moreso than current rating .

Rating formula

TIP rating = 100 / (0.99 * RL 0.3 * RSA 0.4/ RW 0.3)
spin catagory add {+10% * CSPI - CJ * Eff %}

HAF calc number as applied to classes -

added 2nd catagory for upper wind speed .
per outline --sub calc. required ,-
-2nd catagory listed -