This experimental study examines ventilated supercavity formation in a free-surface bounded environment where a body is in motion and the fluid is at rest. For a given torpedo-shaped body and water depth (
$H$
), depending on the cavitator diameter (
$d_{c}$
) and the submergence depth (
$h_{s}$
), four different cases are investigated according to the blockage ratio (
$B=d_{c}/d_{h}$
, where
$d_{h}$
is the hydraulic diameter) and the dimensionless submergence depth (
$h^{\ast }=h_{s}/H$
). Cases 1–4 are, respectively, no cavitator in fully submerged (
$B=0$
,
$h^{\ast }=0.5$
), small blockage in fully submerged (
$B=1.5\,\%$
,
$h^{\ast }=0.5$
), small blockage in shallowly submerged (
$B=1.5\,\%$
,
$h^{\ast }=0.17$
) and large blockage in fully submerged (
$B=3\,\%$
,
$h^{\ast }=0.5$
) cases. In case 1, no supercavitation is observed and only a bubbly flow (B) and a foamy cavity (FC) are observed. In non-zero blockage cases 2–4, various non-bubbly and non-foamy steady states are observed according to the cavitator-diameter-based Froude number (
$Fr$
), air-entrainment coefficient (
$C_{q}$
) and the cavitation number (
$\unicode[STIX]{x1D70E}_{c}$
). The ranges of
$Fr$
,
$C_{q}$
and
$\unicode[STIX]{x1D70E}_{c}$
are
$Fr=2.6{-}18.2$
,
$C_{q}=0{-}6$
,
$\unicode[STIX]{x1D70E}_{c}=0{-}1$
for cases 2 and 3, and
$Fr=1.8{-}12.9$
,
$C_{q}=0{-}1.5$
,
$\unicode[STIX]{x1D70E}_{c}=0{-}1$
for case 4. In cases 2 and 3, a twin-vortex supercavity (TV), a reentrant-jet supercavity (RJ), a half-supercavity with foamy cavity downstream (HSF), B and FC are observed. Supercavities in case 3 are not top–bottom symmetric. In case 4, a half-supercavity with a ring-type vortex shedding downstream (HSV), double-layer supercavities (RJ inside and TV outside (RJTV), TV inside and TV outside (TVTV), RJ inside and RJ outside (RJRJ)), B, FC and TV are observed. The cavitation numbers (
$\unicode[STIX]{x1D70E}_{c}$
) are approximately 0.9 for the B, FC and HSF, 0.25 for the HSV, and 0.1 for the TV, RJ, RJTV, TVTV and RJRJ supercavities. In cases 2–4, for a given
$Fr$
, there exists a minimum cavitation number in the formation of a supercavity while the minimum cavitation number decreases as the
$Fr$
increases. In cases 2 and 3, it is observed that a high
$Fr$
favours an RJ and a low
$Fr$
favours a TV. For the RJ supercavities in cases 2 and 3, the cavity width is always larger than the cavity height. In addition, the cavity length, height and width all increase (decrease) as the
$\unicode[STIX]{x1D70E}_{c}$
decreases (increases). The cavity length in case 3 is smaller than that in case 2. In both cases 2 and 3, the cavity length depends little on the
$Fr$
. In case 2, the cavity height and width increase as the
$Fr$
increases. In case 3, the cavity height and width show a weak dependence on the
$Fr$
. Compared to case 2, for the same
$Fr$
,
$C_{q}$
and
$\unicode[STIX]{x1D70E}_{c}$
, case 4 admits a double-layer supercavity instead of a single-layer supercavity. Connected with this behavioural observation, the body-frontal-area-based drag coefficient for a moving torpedo-shaped body with a supercavity is measured to be approximately 0.11 while that for a cavitator-free moving body without a supercavity is approximately 0.4.