Aft peak tank

The aft peak tank is the aftermost ballast tank in the hull, bounded forward by the aft peak bulkhead and enclosing the stern tube where the propeller shaft exits. It serves as a trim tank: filling or emptying it shifts the center of buoyancy aft or forward to correct longitudinal trim and set propeller immersion. Because it surrounds the stern tube, the aft peak bulkhead is a watertight boundary required by SOLAS Ch II-1 subdivision rules, limiting flooding if the stern tube seal fails. It is normally a seawater ballast tank, vented and sounded like any ballast space.