  We construct a dual pair associated to the Hamiltonian geometric formulation
of perfect fluids with free boundaries. This dual pair is defined on the
cotangent bundle of the space of volume preserving embeddings of a manifold
with boundary into a boundaryless manifold of the same dimension. The dual pair
properties are rigorously verified in the infinite dimensional Fr\'echet
manifold setting. It provides an example of a dual pair associated to actions
that are not completely mutually orthogonal.
