Abstract: The invention relates to an outboard sterntube seal, for the oil-lubricated propeller shaft bearings of a ship, which is equipped with a water-side seal and an oil-side seal separated by a cavity provided with a drain duct leading into the interior of the ship to permit monitoring of the seal. Both the water-side seal and the oil-side seal are in the form of rotating mechanical seals which each include a slipring and a counterring, the oil-side seal being designed in such a manner that in the event of failure of the water-side seal the sealing surface of the oil-side slipring is loaded additionally in its direction of closure through a retaining ring by the water pressure prevailing in the cavity. The sterntube seal is also equipped with additional elements that elastically accommodate movement of the shaft and seal the cavity against oil and water. The sliprings and counterrings of the rotating mechanical seals each have at least two independently removable and circumferentially extending parts.