Abstract: The flow around hollow hemisphere models was investigated in. water channel at B. I. A. A. by hydrogen bubble technique. The flow velocity distribution both in front of and behind the model was measured by hydrogen bubble time lines. It is closed to the values estimated by the irrotational flow theory for the flow right after the start. As the starting vortex grew larger, the flow in the wake is quite, different, A large reversed flow is induced behind the model. Hence, the apparent mass estimated by irrota-tional flow can only be at the beginning. It should be much larger as the starting vortex becomes larger.Sometimes a large vortex in front of model may be formed in the steady flow as shown on plate 3. This vortex is unstable and may cause side force and unstable motion to a parachute. This vortex can be reduced and even be eliminated by holes suitably placed on the model.