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SESK: Stuff Everyone Should Know · sesk.info/boat-one-20b-two-5b

A 30-foot boat without a fixed fire system needs two 5-B extinguishers. What single extinguisher may replace both?

One 20-B extinguisher.

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  1. One 20-B extinguisher ✔
  2. One 10-B extinguisher
  3. One 1-A extinguisher

Why: Boats 26 to under 40 feet with no fixed system need two 5-B extinguishers. The rules let one 20-B count for two 5-B, since the bigger number means more extinguishing agent.

Huh, didn't know that: A fixed fire system in the engine room lowers the number of portable extinguishers you need.

The dad joke
Why did the 20-B extinguisher feel important? It did the work of two.
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References

Answer: One 20-B extinguisher. Boats 26 to under 40 feet with no fixed system need two 5-B extinguishers. The rules let one 20-B count for two 5-B, since the bigger number means more extinguishing agent.

  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
    One 20-B, rated portable fire extinguisher may be substituted for two 5-B portable fire extinguishers
    Checked 2026-10-09.
  2. 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
    The number indicates the amount of the extinguishing agent contained in the extinguisher
    Checked 2026-10-09.

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