Compare a recorded through-water speed and same-condition waterline length with an externally selected speed-length-ratio reference.
Choose your path
Reconcile a recorded STW/LWL speed-length ratio with an external hull/condition-specific reference without calling one coefficient a universal hull-speed limit.
Keep LWL, load/trim/draft and calibrated STW aligned.
Enter the documented LWL, recorded STW and exact-condition external reference ratio.
Sees a reproducible ratio and signed difference rather than a maximum-speed promise.
Avoid mixing LOA, SOG or unrelated hull/reference data.
Compare only same-frame records and inspect the reference speed derived from the entered ratio.
Can trace a discrepancy without grading hull efficiency.
Keep resistance, powering and seaworthiness decisions outside one ratio.
Use builder/designer trials and qualified naval-architecture or marine guidance.
Does not authorize operation or modification from the worksheet.
Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.
Tools you might need next
Estimate theoretical hull speed from waterline length using classic displacement formula. Free hull speed formula tool for hull, speed, and more.
Compare entered immersed geometry and water-density displacement with a documented same-condition displacement reference.
Measure gross and position-matched adjusted typing speed with 15, 30, 60, or 120-second limits, actual elapsed time, accuracy, and local history.
Recorded speed through water is divided by the square root of entered LWL in feet. LWL must describe the same load, trim and draft condition.
The entered external ratio is multiplied by the same square-root LWL to create a comparison speed. The tool does not silently assume 1.34 or any other coefficient applies universally.
The signed difference compares two entered records only. Hull form, displacement, power, propulsor, appendages, loading, depth, wind, waves and current remain external performance factors.
Updated: August 2026
Enter documented same-condition LWL and calibrated STW to reproduce the recorded speed-length ratio.
Enter an exact-hull, exact-condition ratio and inspect the derived reference speed plus signed difference.
Use the arithmetic to organize records, then rely on trials, resistance/powering evidence and qualified marine guidance for consequential decisions.
Use documented waterline length for the same load, trim and draft as the recorded STW.
Treat every coefficient as an entered comparison reference. It does not certify maximum speed, powering, efficiency or seaworthiness.
This worksheet reconciles one recorded STW/LWL ratio with an externally selected same-hull reference. It does not predict resistance, power, maximum speed, efficiency or safe operation.