Engineering:Sail Area-Displacement ratio
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Short description: Calculation used to estimate how much sail a boat carries relative to its weight
The Sail Area-Displacement ratio (SA/D) is a calculation used to express how much sail a boat carries relative to its weight.[1]
- [math]\displaystyle{ \mathit{SA/D} = \frac{\mathit{Sail Area}(\text{ft}^2)} {[\mathit{Displacement}(\text{lb})/64]^{\frac{2}{3}}} = \frac{\mathit{Sail Area}(\text{m}^2)} {\mathit{Displacement}(\text{m}^3)^{\frac{2}{3}}} }[/math]
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+ |
SA/D, however, doesn't 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
References
- ↑ Paris, Jay E. (31 May 2018). "Comparing Design Ratios" (in en-us). https://www.sailmagazine.com/boats/comparing-design-ratios.
- ↑ McGeary, Jeremy (17 October 2012). "How Sailboats Measure Up" (in en-us). https://www.cruisingworld.com/how/how-sailboats-measure/.
- ↑ Sponberg, Eric W.. "The Design Ratios" (in en-us). https://www.ericwsponberg.com/wp-content/uploads/2021/09/THE-DESIGN-RATIOS.pdf.
- ↑ Reisberg, Lars. "Sail Area-Displacement Ratio: Skipper´s Basics". http://no-frills-sailing.com/sail-area-displacement-ratio-skippers-basics/.
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