  We investigate the hydrodynamics of three-dimensional classical Bondi-Hoyle
accretion. A totally absorbing sphere of different sizes (1, 0.1 and 0.02
accretion radii) moves at different Mach numbers (0.6, 1.4, 3.0 and 10)
relative to a homogeneous and slightly perturbed medium, which is taken to be
an ideal, nearly isothermal, gas ($\gamma=1.01$). The hydrodynamics is modeled
by the ``Piecewise Parabolic Method'' (PPM). The resolution in the vicinity of
the accretor is increased by multiply nesting several $32^3$-zone grids around
the sphere, each finer grid being a factor of two smaller in zone size than the
next coarser grid. grids. For small Mach numbers (0.6 and~1.4) the flow
patterns tend towards a steady state, while in the case of supersonic flow
(Mach~3 and~10) and small enough accretors (radius of~0.1 and~0.02 accretion
radii), an unstable Mach cone develops, destroying axisymmetry. The shock cones
in the supersonic models never clear the surface of the accretors (they are
tail shocks, not bow shocks) and the opening angle is smaller (compared to
models with larger $\gamma$) especially for the highly supersonic models. The
densities in the shock cone is larger for models with smaller $\gamma$. The
fluctuations of the accretion rates and flow structures are weaker than in the
corresponding models with larger $\gamma$. The hydrodynamic drag of all models
with accretor sizes of 0.1~$R_{\rm A}$ or smaller acts in an accelerating
direction, while the gravitational drag is always decelerating and larger than
the hydrodynamic drag (thus the net force is decelerating).
