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The sail area-displacement ratio (SA/D) is a calculation used to express how much sail a boat carries relative to its weight.

${\displaystyle {\mathit {SA/D}}={\frac {{\mathit {SailArea}}({\text{ft}}^{2})}{^{\frac {2}{3}}}}={\frac {{\mathit {SailArea}}({\text{m}}^{2})}{{\mathit {Displacement}}({\text{m}}^{3})^{\frac {2}{3}}}}}$

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:

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

1. Paris, Jay E. (31 May 2018). "Comparing Design Ratios". Sail Magazine. Retrieved 9 July 2020.
2. McGeary, Jeremy (17 October 2012). "How Sailboats Measure Up". Cruising World. Retrieved 9 July 2020.
3. Sponberg, Eric W. "The Design Ratios" (PDF). Sponberg Yacht Design Inc. Retrieved 9 July 2020.
4. Reisberg, Lars. "Sail Area-Displacement Ratio: Skipper´s Basics". No frills sailing. Retrieved 11 July 2020.

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