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SESK: Stuff Everyone Should Know · sesk.info/boat-no-plate-formula

No capacity plate? The rule of thumb for maximum persons is length times width divided by what?

Divided by 15. (length x width / 15)

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  1. Divided by 10
  2. Divided by 15 ✔
  3. Divided by 25

Why: Multiply the boat's length by its width in feet, then divide by 15. An 18 foot boat that is 5 feet wide gives 90 / 15 = 6 people, in good weather.

Huh, didn't know that: The formula is meant for boats under 20 feet and does not account for gear weight.

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Why was the boat good at math? It always knew its limits.
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References

Answer: Divided by 15. Multiply the boat's length by its width in feet, then divide by 15. An 18 foot boat that is 5 feet wide gives 90 / 15 = 6 people, in good weather.

  1. USCG, A Boater's Guide to the Federal Requirements for Recreational Boats (Nov 2023) www.uscgboating.org/assets/1/AssetManager/Boaters-Guide-to-Federal-Requirements-for-Receational-Boats-20231108.pdf
    Maximum Number of Persons = Boat Length X Boat Width/15.
    Checked 2026-10-09.
  2. NASBLA ESP TR 103-2022, Basic Boating Knowledge Core Plus Power technical report higherlogicdownload.s3.amazonaws.com/NASBLA/76594a34-f3a1-4916-95ac-1e9c872170cc/UploadedImages/education/national-education-standards/ESP_TR_ESP_103_Core_Plus_Power_2022_06_01FINAL.pdf
    This calculation represents the number of persons (weighing 150* pounds each, on average) the boat can carry safely in good weather conditions.
    Checked 2026-10-09.

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