Bow Wave & Wake Wavelength Calculator
Read any boat's speed from its wake: wavelength of the transverse wave system at a given speed — or speed from an observed wavelength.
Wake-reading is free speed telemetry: count the feet between a passing boat's transverse crests, take √ and × 1.34, and you have her speed. At her own hull speed, the crest spacing equals her waterline — visible from the dock.
Formula
⚠️ For planning and education only — verify with your vessel's documentation, naval-architecture data and official sources. Not for navigation or stability decisions on real voyages without professional data.
Read any boat's speed from its wake: wavelength of the transverse wave system at a given speed — or speed from an observed wavelength.
About Bow Wave & Wake Wavelength Calculator
A boat's wake is a speedometer broadcast in public: deep-water waves travel at 1.34√λ knots, so the spacing between a wake's transverse crests encodes exactly how fast the boat that made them was going. This calculator runs the relation both ways — speed to wavelength, and (mentally inverted) wavelength back to speed — plus the wave period a moored observer would time. It's the hull-speed formula seen from outside the boat.
How to use Bow Wave & Wake Wavelength Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula λ(ft) = (V/1.34)² — invert the hull-speed relation; deep-water wave: λ = 2πV²/g substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Bow Wave & Wake Wavelength Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula λ(ft) = (V/1.34)² — invert the hull-speed relation; deep-water wave: λ = 2πV²/g with sources cited on the page
- ✓Wake-reading is free speed telemetry: count the feet between a passing boat's transverse crests, take √ and × 1.34, and you have her speed. At her own hull speed, the crest spacing equals her waterline — visible from the dock.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
How do I actually estimate a wake's wavelength on the water?+
Reference lengths you know: your own boat (a 30-footer spanning crest-to-crest means λ ≈ 30 ft → the maker was doing ~7.3 kt), dock sections, or timed period from a fixed point (λ = 5.12 × T² in feet). The transverse waves — the ones following parallel behind the boat — are the measurement; the V-shaped diverging waves are a different family.
What is the Kelvin wake pattern?+
Lord Kelvin proved every displacement vessel in deep water drags the same wedge: diverging waves forming the V's arms and transverse waves across it, all contained in a half-angle of 19.47° regardless of speed or size — duck or supertanker. Speed changes the wavelengths within the pattern (this tool's subject), not the wedge's angle.
Why do big ship wakes feel so different from boat wakes?+
Wavelength scales with V²: a tanker at 15 kt lays transverse waves 125 ft long — your 30-ft boat rides them like gentle swell. A cruiser at 8 kt lays 36-ft waves that the same boat meets as steep chop. Wake discomfort is about YOUR length relative to THEIR wavelength, which is why mid-size powerboat wakes annoy everyone equally.
Does this work for judging a speeding boat in a no-wake zone?+
Educationally, yes — the wake doesn't lie: crests 16 ft apart mean ~4.6 kt no matter what the throttle claims. (Enforcement uses other tools, but the physics is the same.) More usefully, reading your OWN wake calibrates a failed speed log: a glance astern at crest spacing against the hull gives speed within half a knot.
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