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Units feet · pounds · gallons meters · kilograms · liters Activity Sailing Power Fishing

What do these numbers mean?

Hull speed

The practical top speed of a displacement hull under most conditions, calculated as 1.34 × √LWL (waterline length in feet). As a boat speeds up it digs a trough between its own bow and stern waves; at hull speed that wave is as long as the waterline and pushing harder mostly makes a bigger wave, not a faster boat. A longer waterline means a higher hull speed — which is why a 40-footer passes a 30-footer on the same breeze. Surfing down waves or planing can exceed it, but for passage planning treat it as your realistic ceiling.

SA/D — sail area to displacement

The boat’s power-to-weight ratio: working sail area divided by displacement (in cubic feet) to the 2/3 power. Think horsepower per pound. Under 15: underpowered, needs real wind to move well. 16–18: classic cruiser — comfortable, needs 12+ kt to reach hull speed. 18–22: performance cruiser, lively in light air. Over 22: race boat, reefs early. Higher SA/D means more speed in the light stuff — exactly what matters on a 5-knot Great Lakes afternoon.

D/L — displacement to length

How heavy the boat is for its waterline length (displacement in long tons ÷ (0.01 × LWL)³). Under 100: ultralight racer. 100–200: light — quick, more active motion. 200–300: moderate — most classic cruisers live here; good compromise of speed, comfort, and load carrying. Over 300: heavy — soft, steady ride, slower in light air, shrugs off chop. Lighter boats accelerate faster; heavier boats keep momentum through waves.

Bal/D — ballast ratio

What share of the boat’s total weight is ballast in the keel. Typical keelboats run 35–45%. More ballast (or the same ballast placed deeper) makes a boat stiffer — it stands up to its sails instead of heeling over and slowing down. Two boats with the same percentage can still differ: a deep lead bulb works much harder than shallow internal ballast.

ORC performance / certificate

The Offshore Racing Congress measures real boats — hull, weight, righting moment, sails — and runs them through a velocity prediction program (VPP). The numbers shown come from an actual measured certificate of this model (the year shown). “Nearest match” means no certificate exists for your exact model, so the closest sistership by name and length is shown — treat it as a good approximation, not gospel.

GPH — general purpose handicap

The boat’s predicted time to sail one nautical mile around an all-around course, in seconds per mile. Lower is faster. It’s the single number race committees use to compare different boats: the difference in GPH times the course length is the time one boat owes the other. Example: a boat rating 601 s/mi owes a boat rating 629 s/mi about 28 seconds every mile — roughly 4½ minutes over a 10-mile race.

OSN — offshore single number

Same idea as GPH (seconds per mile, lower = faster) but weighted for offshore wind mixes rather than round-the-buoys courses. Clubs use it for simple time-on-distance scoring on point-to-point and distance races.

Reading the polar diagram

Each curve is one true wind speed (the number at the curve’s end, in knots). Straight up is dead into the wind; the angle around the arc is the true wind angle off the bow, and the distance from the center is boat speed (the rings, in knots). Follow a curve and you can see the boat is slowest pinching upwind, fastest on a beam or broad reach (90–135°), and slows again dead downwind — which is why racers jibe downwind through the angles instead of sailing straight at the mark. Hover any point for the exact numbers.

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