Sail area-displacement ratio
The sail area-displacement ratio (SA/D) is a calculation used to express how much sail a boat carries relative to its weight.[1]
![{\displaystyle {\mathit {SA/D}}={\frac {{\mathit {SailArea}}({\text{ft}}^{2})}{[{\mathit {Displacement}}({\text{lb}})/64]^{\frac {2}{3}}}}={\frac {{\mathit {SailArea}}({\text{m}}^{2})}{{\mathit {Displacement}}({\text{m}}^{3})^{\frac {2}{3}}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/cc09ac51e8c8f8c4dbb61d20588dc0bd471aee4b)
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.[2] The higher the SA/D, the more lively the boat's sailing performance:[3]
| 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.[4]
See also
[edit]References
[edit]- ^ Paris, Jay E. (31 May 2018). "Comparing Design Ratios". Sail Magazine. Retrieved 9 July 2020.
- ^ McGeary, Jeremy (17 October 2012). "How Sailboats Measure Up". Cruising World. Retrieved 9 July 2020.
- ^ Sponberg, Eric W. "The Design Ratios" (PDF). Sponberg Yacht Design Inc. Retrieved 9 July 2020.
- ^ Reisberg, Lars. "Sail Area-Displacement Ratio: Skipper´s Basics". No frills sailing. Retrieved 11 July 2020.
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