Ship launching is a critical milestone after the completion of the building period on a slipway or in a dock. It marks the transition of the hull from land‑based support to a floating state. The impact forces, buoyancy changes, and hull stress distribution during launching pose severe tests to the hull strength, watertight integrity, and equipment securing. Depending on the vessel type and the yard’s facilities, Jiangsu Haizhongzhou Shipping Industry Co., Ltd. uses two techniques – gravity slipway launching and floating dock launching – and has developed a mature risk control system for each.
Gravity slipway launching is suitable for small and medium‑sized vessels built on slipways. The slipway longitudinal slope at Jiangsu Haizhongzhou Shipping Industry Co., Ltd. is designed between 1:10 and 1:12. Launching cradles are lubricated with grease, and holding devices are installed. Before launching, the technical team performs the following calculations and checks: precise measurement of the vessel’s centre of gravity to ensure it lies within the longitudinal stability range of the cradles; dynamic calculation of hull buoyancy throughout the launching process to predict the stern squat when the vessel begins to float at the end of the slipway; and measurement of the coefficient of friction between the cradles and the slipway, which is normally controlled below 0.03. At the same time, the hull shell area in contact with the cradles is reinforced, and temporary supports are fitted to prevent local deformation during launching.
The launching operation is initiated by a single trigger, using explosive release gear or hydraulic release units. Once the hull begins to move, monitoring personnel record the sliding speed, acceleration, and trajectory in real time using high‑speed cameras and sensors. For a 48,000 DWT bulk carrier, for example, the entire process from release to full flotation took only 18 seconds, with a sliding distance of 110 m and a maximum sliding speed of 6.5 m/s. After the hull enters the water, tugs immediately take over and tow the vessel to the outfitting quay for subsequent work.
For large vessels or where site water conditions are restricted, Jiangsu Haizhongzhou Shipping Industry Co., Ltd. uses floating dock launching. The core principle is to sink the floating dock together with the completed vessel, allowing the vessel to float by its own buoyancy. This method places higher demands on the watertightness of the dock, the reliability of the ballast system, and temporary mooring. Before each launch, the company performs a tightness test of the dock’s ballast tanks, tests the filling and draining capacity of each ballast pump, and installs temporary fenders on the dock wings. During the sinking process, a strict staged ballasting procedure is followed to maintain the dock’s levelness and prevent contact between the hull and the dock wings.
Immediately after launching, Jiangsu Haizhongzhou Shipping Industry Co., Ltd. inspects the underwater portion of the hull, including shell plate welds, the propeller, the rudder, sea chest gratings, and zinc anodes, to confirm there is no damage or abnormality. At the same time, the main engine, shafting, generators, and other equipment are checked for any water ingress or looseness. All inspection data are entered into the vessel’s construction archive.
From slipway launches to floating dock launches, the technical team at Jiangsu Haizhongzhou Shipping Industry Co., Ltd. has accumulated practical experience from nearly one hundred vessels. Each launch is a precise technical collaboration, and a direct reflection of the shipyard’s construction capability.
