NSC - Keel Boat Metrics Calculator

Use the following form to calculate a boat standard metrics. The formulae are given at the end of this page.

The pre-loaded measurements are that of a Tanzer 7.5 - Just override them with your own values, then click the Calculate! button.

For more information, Sailing USA offers a full treatment of the subject of stability and design, including discussions and references.

Select a Unit System:    British (ft, lb)    Metric (m, kg) (Please be consistent or the results will be meaningless)
Your Boat Measurements:
Length Over All - LOA (ft or m)
Load Waterline Length - LWL (ft or m)
Beam (ft or m)
Displacement (lb or kg)
Ballast (lb or kg)
Total Sail Area - Staysails(s) + Main (ft2 or m2)
Your Boat Standard Metrics:
Displacement (Long Tons)
Sail Area/ Displacement Ratio 12 = low, >20 = generous
Displacement/ Length Ratio ultra light<100, 140<light>175, 200<moderate>280, 300<heavy>350
Theoretical Hull Speed (Kts)
Motion Comfort Overall comfort when under way: the higher, the better
Balast / Displacement Ratio (%) 33% avg, 40% stiff
Screen Number ability to resist capsize: <2 good for ocean crusing yachts

Metrics formulae (in British system)
Metric	Formula
Sail Area - Displacement Ratio	Sail Area / (Displacement in Cubic Feet)2/3
Displacement - Length Ratio	Long Ton displacement / (0.01 * LWL)3
Theoretical Hull Speed	1.34 * Square Root of LWL
Motion Comfort	Displacement / ( 2/3 * ((0.7 * LWL) + (1/3 *LOA)) * Beam3/4 )
Balast - Displacement Ratio	ballast/ displacement x 100
Capsize Screening Formula	Beam / (Displacement in Cubic Feet)1/3
In the above formulae: Displacement in Cubic Feet = displacement in lbs / 64 Displacement in Long Tons = displacement in lbs / 2240