  The three-nucleon bound and scattering equations are solved in momentum space
for a coupled-channel Hamiltonian. The Hamiltonian couples the purely nucleonic
sector of Hilbert space with a sector in which one nucleon is excited to a
$\Delta$ isobar. The interaction consists of irreducible two-baryon and
irreducible three-baryon potentials. The calculation keeps only the purely
nucleonic one among the irreducible three-baryon potentials. The
coupled-channel two-baryon potential yields additional reducible contributions
to the three-nucleon force. The Coulomb interaction between the two protons is
included using the method of screening and renormalization. Three-nucleon force
effects on the bound-state energies and on observables of elastic
nucleon-deuteron scattering and breakup are studied.
