Marine Hull Speed Calculator
Calculate a displacement-hull reference from your waterline length in feet or metres.
A QUICK WALKTHROUGH
How to use this tool
- Enter a positive waterline length, not overall hull length.
- Choose feet or metres, then calculate the reference.
- Calculate, then copy the report or download TXT.
Calculation
Reference (kn) = 1.34 × √LWL(ft). Metres convert to feet by dividing by 0.3048.
What the result covers
Bowditch Volume II (2019), §402 gives this approximation and notes dependence on hull shape. This is a displacement-hull reference, not a maximum speed, planing range or safe operating speed. It does not model power, loading, sea state or hull-specific performance.
Local processing
Inputs remain in your browser. Copy and TXT download contain your inputs, results, formula and scope note.
GOOD TO KNOW
Common questions
Is this a vessel's maximum speed?
No. It is a length-based approximation; actual performance depends on the vessel and conditions.
Which length is required?
Use waterline length, in the unit selected. Do not substitute overall length.