Neutral buoyancy is a state in which an object neither sinks nor floats because its weight is balanced by buoyant force.

A boat floating at the surface is in balance: the boat’s weight (downward force) is equal to the buoyant force (the weight of the water displaced by the hull).

If more divers board the boat, the total weight increases and the boat sits lower in the water. It will settle again when it displaces enough water for the buoyant force to match the new total weight.

If too many divers board, the boat will sink so low that water may flood in. Once flooding occurs, the boat can lose buoyancy and may sink.