What is a Ballast Ratio (keel %)?

The Ballast Ratio is the amount of ballast a design is carrying. This ratio is often displayed as a percentage. The higher the percentage, the greater the righting moment, i.e. better ability to resist heeling. The calculation is very popular because its simplicity and the fact that the values of ballast and the displacement are easily available. The article relates the Ballast Ratio to thousands of sailboats.

Ballast ratio

Nomenclature

Abrev.	Unit	Description
Ballast	kg	The weight of the keel
Disp.	kg	Displacement

The unit can actually be kg, ton, lbs, or any other weight unit as long as it is the same for both ballast and displacement.

This figure shows the scattering of the Ballast ratio for thousands of sailboat designs. Each dot represent a specific design. The figure shows that the most designs has a ballast ratio in the range 30 - 50 %.

This figure shows the mean value of the Ballast Ratio as function of the length of the hull. The vertical lines shows the uncertainty in the statistics. If the sample is low - which they are for sailboats < 6 meters (15 feet) and sailboats > 15 meters (45 feet) - then the uncertainty is high, i.e. long lines. The largest keel % is for 10 meter (33 ft) boats, which is 41 % in average.