Sail Area/Displacement: sail for weight
SA/D compares sail area with a displacement-related scale.
Conventional formula
SA/D = sail_area_ft² / (displacement_lb / 64)^(2/3)In plain language
The convention uses square feet of sail area and pounds of displacement. Displacement is divided by 64, a conventional salt-water density, and raised to the two-thirds power.
How to interpret it
More SA/D means more sail relative to stated weight. It may suggest light-air potential and more need to reef without guaranteeing a speed.
Why it matters
It is useful when the compared sail areas use the same measurement method.
Limitations
An actual genoa, theoretical foretriangle and additional sails provide different bases. Hull shape, sail condition and crew are outside the formula.
In practice
If the source does not identify the sail-area basis, show that ambiguity before comparing figures.
Sources & reading
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