A pontoon being able to float is not enough. A buyer needs to know how it floats at its operating load and how much reserve remains.
Core quantities
- displacement of pontoon itself
- dead load of fixed equipment
- live load of users
- concentrated equipment load
- reserve buoyancy
- unloaded freeboard
- design loaded freeboard
- trim
- heel under eccentric loading
- damage/flooded-float scenario if specified
For fresh water, one cubic metre of displaced water provides approximately one tonne of buoyancy before subtracting pontoon mass. Salt water is slightly denser. Real designs must account for geometry, immersion and safety margins rather than using that rough rule as a design calculation.
Buyer test
Ask the builder to state:
- total nominal float volume
- pontoon dead mass
- design live load
- loaded draft/freeboard
- maximum permitted load
- whether one damaged float is considered
- whether floats are sealed, inspectable, ballastable or foam filled
Freeboard by use
- rowing/kayak/dinghy: deliberately low
- small runabout berth: low-medium
- yacht/marina: medium
- large commercial facility: generally higher and heavier
There is no universal ideal number. It should align with the vessel's boarding height, wake environment and reserve-buoyancy requirement.