More about D/L and SA/D Ratios
As stated in our Uniform Sailing Instructions and website postings, we are using these ratios to determine eligibility for our various racing classes. The values we are using are those in the US SAILING dimensions database and are also documented in our Quickbase Scratch Sheet.
The ratios are in common use in naval architecture to objectively categorize sailboat types and performance. D is displacement, L is length and SA is sail area but this is where the simplicity ends. Why would anything in sailboat racing be simple!
The formulas to calculate the ratios are as follows ;
D/L = Weight in long tons/ (0.01x waterline length in feet)3
SA/D = Sail are in sq feet / (displacement in cubic feet)2/3
where sail area is the fore triangle area plus the main triangle area not including jib overlap or main roach.
The displacement values in the database are taken from manufacturers brochures and we are cautioned by US SAILING regarding their accuracy. I have found one or two fairly large discrepancies but none that would put a CORA boat in a different class.
If you want to check your numbers out and don’t know what a long ton is, you have forgotten how to cube or raise a number to the 2/3 power or what made Archimedes say eureka , there are a number of web sites that will do it for you. Try:
http://www.sailingusa.info/cal__dl_ratio.htm
http://www.sailingusa.info/cal__sad_ratio.htm
David Anderson
CORA Measurer