https://continuouswave.com/whaler/refer ... tedHP.html
The method to calculate weight capacity for an outboard boat is given in federal regulations at 33 CFR § 183.35 - Maximum weight capacity: Outboard boats. See
https://www.law.cornell.edu/cfr/text/33/183.35
To calculate the maximum weight capacity, two different weights must be known:
- Boat Weight, which is the sum of
- Hull weight;
- Deck and superstructure weight;
- Weight of permanent appurtenances; and
- Weight of full permanent fuel tanks.
- Maximum Displacement, which is the weight of the volume of water displaced by the boat at its maximum level immersion in calm water without water coming aboard except for water coming through one opening in the motor well with its greatest dimension not over three inches for outboard motor controls or fuel lines.
The regulations also provide a method to calculate when the boat is level.
The practical way to know the weight of water displaced at maximum level immersion is to record the amount of weight added to the boat to decrease the freeboard to the specified level, “without water coming aboard,” and add this to the boat weight. The difference is then the amount of weight added. The regulation then limit the rated capacity to only one-fifth of the difference. This means that the hull remains far above its maximum possible immersion without taking on water when loaded to its specified capacity. The “bureaucrats” that developed the regulation were probably senior officers in the U.S. Coast Guard. To know when a boat is loaded to its rated capacity there remains at least four-fifths of its reserve buoyancy seems quite safe to me.
Again, these capacities are a result of the federal Boat Safety Act of 1971. The purpose of the act was to promote safe boating.