Draft and Freeboard Change Calculator
Calculate signed draft and opposite freeboard change using a constant direct or user-estimated waterplane area.
A QUICK WALKTHROUGH
How to use this tool
- Choose direct area or enter positive waterline length, beam and your factor to estimate area.
- Enter signed added mass and positive water density, then calculate.
- Calculate, then copy the report or download TXT.
Calculation
Estimated A = LWL × beam × factor. Δdraft = added kg ÷ (A × density). Δfreeboard = −Δdraft. kg/cm = A × density ÷ 100.
What the result covers
A constant-waterplane approximation for small changes only. Positive mass increases draft; negative mass represents removal. It does not calculate trim, stability, payload permission or large-immersion changes. No density or area factor is supplied or recommended.
Local processing
Inputs remain in your browser. Copy and TXT download contain your inputs, results, formula and scope note.
GOOD TO KNOW
Common questions
Can I enter removed mass?
Yes. Use a negative added mass; the arithmetic draft change becomes negative and freeboard change positive.
Which area mode should I use?
Direct uses your supplied area. Estimate multiplies your dimensions by your supplied factor; neither mode verifies hull geometry.