Keelboat Metrics Calculator | Nepean Sailing Club

Usage

Use the following form to calculate a sailboat 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 on sailboat metrics, consult the Ted Brewer Yacht Design website.

The Calculator

Your Boat Measurements:

Select a Unit System (Please be consistent or the results will be meaningless):
British (ft, lb) Metric (m, kg)
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
Ballast / Displacement Ratio (%):
33% avg, 40% stiff
Screen Number:
Ability to resist capsize
< 2, good for ocean crusing yachts

Metrics formulae explained:

All figures are based on the British Measurement Mystem.

Note: some Displacements are in British Tons (2,000 lbs), some in Long Tons (2,240 lbs).

Metrics	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 * (LWL)^1/2
Motion Comfort	Displacement / { 2/3 * [ (0.7 * LWL) + (1/3 * LOA) ] * Beam^4/3 }
Ballast - Displacement Ratio	(Ballast / Displacement) * 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 / 2,240

Calculator designed by D. Servranckx. Page updated on 2022-11-26.

********** NOTE: This page must be edited as "the Boss". ********** Update log: 2022-11-26_ DS: fixed "balast" to "ballast" spelling. 2022-08-16: DS: minor display tweaks. 2022-01-12: DS: updated default Tanzer 7.5 data using Wikipedia data. 2022-01-11: DS: changed the Motion Confort formula TEXT to show (4/3) instead of (3/4) 2021-04-30: DS: added this section. replaced "Keel Boat" with "Keelboat"

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