A seal arrangement for sealing around a rotating shaft that passes through a ship bulkhead includes an expandible and contractible seal ring made of several seal ring segments, and radial actuators that engage the seal ring segments and can be power-activated, e.g. with a pressure medium, to pull the seal ring segments radially outwardly, thereby expanding the seal ring to a larger diameter spaced away from the shaft. When the radial actuators are not activated, the biasing force of springs contracts the seal ring segments to a smaller diameter, to establish sealing contact of the seal ring on the shaft. In normal operation a control unit activates the actuators, but if sensors detect a power failure or water in the ship, or a manual switching is triggered, then the seal arrangement contracts under spring force into the sealing condition with the seal rings sealing against the shaft.