Simple answer. The buoyancy force is equal to the water
displaced by the boat.
If you boat weighs 5000kg, it will displace 5000kg of water
when it floats, and that is the buoyancy force.
Now, make a hole underwater in the boat, it will start to fill with water rather than displace water, and will eventually sink, unless of course it has some sealed buoyancy tanks
, in which case it will sink until the volume of water displaced by those tanks
equals the weight of the boat, plus the weight of the water in the boat.