Fresh Water Allowance (FWA) Calculator
A comprehensive suite for ship stability and load line calculations. Designed for Deck Officers, maritime students, and cargo surveyors.
Purpose: Calculate the Fresh Water Allowance (FWA)—the distance the vessel's draft changes when moving between Salt Water (1.025) and Fresh Water (1.000).
Enter displacement and TPC/TPI to see the result
⚙️ How to Use
Step 1: Displacement
Enter the ship's current displacement in metric tonnes or tons.
Step 2: TPC or TPI
Input the Tonnes Per Centimeter (TPC) or Tons Per Inch (TPI) from the ship's hydrostatic scales.
Step 3: Result
The calculator will provide the Fresh Water Allowance in mm, cm, meters, and inches.
Pro Tip: Use a certified hydrometer to measure dock water density. Even small variations can impact your vessel's draft and safety margins.
📘 Formula Reference
Fresh Water Allowance (FWA)
Metric: FWA (mm) = W / (4 × TPC)
// W = Displacement (tonnes), TPC = Tonnes Per Centimeter
Imperial: FWA (inches) = W / (40 × TPI)
// TPI = Tons Per Inch
Dock Water Allowance (DWA)
DWA = FWA × (1.025 - RD) / 0.025
// RD = Measured Dock Water Density
Draft Change
Change = [(RD₁ - RD₂) × FWA] / 0.025
// RD₁ = Initial RD, RD₂ = Target RD
// Pos (+) = SINKING, Neg (-) = RISING
Standard Densities