46 CFR §142.230

1. (a)Towing vessels of 65 feet or less in length must carry at least the minimum number of portable fire extinguishers set forth in table 142.230(a).
2. (b)Towing vessels of more than 65 feet in length must carry—
   1. (1)At least the minimum number of portable fire extinguishers set forth in table 142.230(b); and
   2. (2)One 40-B portable fire extinguisher fitted in the engine room for each 1,000 brake horsepower of the main engines or fraction thereof. A towing vessel is not required to carry more than six additional 40-B portable fire extinguishers in the engine room for this purpose, regardless of horsepower.
3. (c)The frame or support of any semi-portable fire extinguisher fitted with wheels must be welded or otherwise permanently attached to a steel bulkhead or deck to prevent it from rolling under heavy sea conditions.
4. (d)Extinguishers with larger numerical ratings or multiple letter designations may be used if the extinguishers meet the minimum requirements of this section.