Sail area-displacement ratio

Template:Short description Template:Use dmy dates Template:Use American English The sail area-displacement ratio (SA/D) is a calculation used to express how much sail a boat carries relative to its weight.

$𝑆𝐴/𝐷=\frac{𝑆𝑎𝑖𝑙𝐴𝑟𝑒𝑎({\text{ft}}^2)}{[𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡(\text{lb})/64{]}^{\frac{2}{3}}}=\frac{𝑆𝑎𝑖𝑙𝐴𝑟𝑒𝑎({\text{m}}^2)}{𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡({\text{m}}^3{)}^{\frac{2}{3}}}$

In the first equation, the denominator in pounds is divided by 64 to convert it to cubic feet (because 1 cubic foot of salt water weights 64 pounds). The denominator is taken to the 2/3 power to make the entire metric unit-less (without this, the denominator is in cubic feet, and the numerator is in square feet).

It is an indicator of the performance of a boat. The higher the SA/D, the more lively the boat's sailing performance:

Boat Type	SA/D
Motorsailers	13 - 14
Slow auxiliary sailboats	14 - 15
Average offshore cruisers	15 - 16
Coastal cruisers	16 - 17
Racing yachts	17 - 19
Ultra light racers, class racers, daysailers	20+

The SA/D, however, does not provide information about a boat behavior in a storm or upwind. A polar diagram from a velocity prediction program gives a more precise view.

See also

• Displacement–length ratio

References

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