Calculate total ballast, total displacement, or ballast displacement ratio from any two values with support for lbs, kg, short tons, and metric tons.
- All Miscellaneous Calculators
- Ballast Weight Calculator
- Boat Gross Tonnage Calculator
- Boat Draft Calculator
Ballast Displacement Ratio Formula
The ballast displacement ratio compares the weight of a boat’s ballast to its total displacement. The calculator treats the ratio as a decimal value, not a percent.
BDR = TB / TD
TB = TD * BDR
TD = TB / BDR
- BDR = ballast displacement ratio, unitless
- TB = total ballast
- TD = total displacement
The calculator can solve for any one missing value when you enter the other two:
- To find ballast displacement ratio: divide total ballast by total displacement.
- To find total ballast: multiply total displacement by the ballast displacement ratio.
- To find total displacement: divide total ballast by the ballast displacement ratio.
Total ballast and total displacement must use compatible weight units. The calculator converts pounds, kilograms, short tons, and metric tons internally before applying the formula.
Ballast Displacement Ratio Reference Values
Ballast displacement ratio is often shown as a decimal or as a percentage. To convert the calculator’s decimal result to a percent, multiply by 100.
| Decimal Ratio | Percent | Meaning |
|---|---|---|
| 0.20 | 20% | Ballast is 20% of total displacement. |
| 0.30 | 30% | Common moderate value for many sailboats. |
| 0.40 | 40% | Higher ballast share, often associated with more stiffness. |
| 0.50 | 50% | Very high ballast share for most designs. |
| Unit | Equivalent in Pounds | Use in the Calculator |
|---|---|---|
| 1 lb | 1 lb | Base unit for internal calculation. |
| 1 kg | 2.2046 lb | Converted before calculating the ratio. |
| 1 short ton | 2,000 lb | Used for US ton measurements. |
| 1 metric ton | 2,204.6226 lb | Used for tonne measurements. |
Example Calculations
Example 1: Find the ballast displacement ratio
A sailboat has a total displacement of 12,000 lb and total ballast of 4,200 lb.
BDR = 4200 / 12000 = 0.35
The ballast displacement ratio is 0.35, or 35%.
Example 2: Find total ballast
A boat has a total displacement of 8,000 kg and a ballast displacement ratio of 0.32.
TB = 8000 * 0.32 = 2560 kg
The total ballast is 2,560 kg.
FAQ
Is ballast displacement ratio the same as ballast percentage?
They describe the same relationship, but the format is different. A ballast displacement ratio of 0.35 equals a ballast percentage of 35%. To convert a ratio to a percentage, multiply by 100.
Should total displacement include ballast?
Yes. Total displacement is the full weight of the boat as it displaces water, including hull, rig, equipment, ballast, tanks, and other carried weight depending on the displacement figure being used.
Does a higher ballast displacement ratio always mean a boat is more stable?
Not always. A higher ratio means more of the boat’s displacement is ballast, but stability also depends on hull shape, beam, ballast location, keel depth, center of gravity, and loading. The ratio is useful for comparison, but it is not a complete stability measurement.
