Sailboat Performance Ratios (SA/D and DLR)

Two dimensionless ratios that characterize a sailboat's power and heft, read off the specs by a surveyor, designer, or shopper. Sail area-to-displacement (SA/D) = sail area / (displacement/64)^(2/3) -- sail carried for its size, its power-to-weight: under 16 heavy/under-canvassed, 16-20 moderate cruiser, over 20 performance/racer. Displacement-to-length (DLR) = (displacement/2240 long tons) / (0.01 x LWL)^3 -- weight for its length: under 100 ultralight, 100-200 light, 200-300 moderate, over 300 heavy full-keel. A 500 sq ft, 10,000 lb, 30 ft-waterline boat has SA/D 17.2 (moderate) and DLR 165 (light). A bigger rig or lighter hull raises SA/D; a heavier boat on a shorter waterline raises DLR. Comparative screens; the loaded displacement, measured sail/waterline, and a naval architect's VPP analysis govern real performance.

displaced_volume_ft3 = displacement_lb / 64; sa_d_ratio = sail_area_sqft / displaced_volume_ft3^(2/3); dl_ratio = (displacement_lb / 2240) / (0.01 x lwl_ft)^3.

Sailboat performance ratios (sail area-to-displacement and displacement-to-length; Skene's Elements of Yacht Design; Gerr, The Nature of Boats), by name; the loaded displacement, the measured sail area and waterline, and a naval architect's velocity-prediction analysis govern real performance.

The two ratios are public yacht-design practice; the sail area, displacement, and waterline length are the boat's published or measured particulars.

Estimate. AHJ and licensed professional govern.

Field names used by the API: sail_area_sqft, displacement_lb, lwl_ft, sa_d_ratio, dl_ratio

• SA/D and DLR SA/D = sail area / (disp/64)^(2/3); DLR = (disp/2240) / (0.01 x LWL)^3; 64 lb/ft^3 seawater, 2240 lb/long tonSkene's / Gerr yacht-design practice
• Interpretation bands SA/D <16 heavy, 16-20 moderate, >20 performance; DLR <100 ultralight, 100-200 light, 200-300 moderate, >300 heavy; comparative screens, not a VPPyacht-design convention