  The three-gluon glueball states are studied with the generalization of a
semirelativistic potential model giving good results for two-gluon glueballs.
The Hamiltonian depends only on 3 parameters fixed on two-gluon glueball
spectra: the strong coupling constant, the string tension, and a gluon size
which removes singularities in the potential. The Casimir scaling determines
the structure of the confinement. Low-lying $J^{PC}$ states are computed and
compared with recent lattice calculations. A good agreement is found for
$1^{--}$ and $3^{--}$ states, but our model predicts a $2^{--}$ state much
higher in energy than the lattice result. The $0^{-+}$ mass is also computed.
