Draw a freebody diagram, it will explain it really well
the boat is floating on top of the water, which means that the net acceleration in the y direction must be zero
the boat is not sinking (dominant downwards acceleration/force)
the boat is not flying (dominant upward acceleration/force)
that measn

now, if you drew the FBD, you only have 2 forces acting on the boat.
the upward bouyancy force on the boat and the downward force due to weight

since the net force is equal to zero

and thus
