A shiplift is a modern alternative for a slipway, a floating dry dock or a graving dry dock. A shiplift is used to dry dock and launch ships. It consists of a structural platform that is lifted and lowered exactly vertically, synchronously by a number of hoists. First, the platform is lowered underwater, then the ship is floated above the support, and finally the platform with shipsupport and ship is lifted and the ship is brought to the level of the quay.
Nowadays, shiplift are most of the time supplied under rules of a classification authority. Lloyd's Register of Shipping is the authority with most experience in the certification or classification of shiplifts. Whereas "shiplift" is the word that is normally used, the term used by Lloyd's register is "Mechanical Lift Dock".
It will be discerned between two different kinds of platform design, the articulated and the rigid. The articulated platform has hinged connections between the main and the longitudinal beams, this type is amongst other things favored by Syncrolift and TTS. At the rigid platform, the beams are bolted or welded together. The advantage of the rigid system is a better load distribution and the safety against rope break. This type is amongst other things favored by WETEC Group and TTS.
The Syncrolift System was invented by Raymond Pearlson, who was later awarded the Sperry Award for the invention, development and worldwide implementation of a new system for lifting ships out of the water for repair and for launching new ship construction.
It is important to synchronize the winches. Modern systems use electrical control and drive systems for the winches. Old fashioned electrically driven shiplift systems needed so much starting current that they often could only be used in the weekend when other electrical equipment was not in use. The modern shiplifts however do not have this disadvantage; they can start the movement in any desired curve.
Many shiplifts use a transfer system for ships so that the vessels can be transported from the water to a parking place where they can be painted or repaired. One shiplift can serve many parking places, while a dry docking installation can only dock one ship.
For large vessels the transfer system consists of a number of trolleys or cradles, supported by high capacity steel wheels. The wheels drive on heavy duty rails. The transport can be one directional, but in order to serve more parking places, two directional systems are used. These two directional systems make use of a traverser carriage or sometimes the wheels of the trolleys can be turned over 90 degrees. Above the wheels often hydraulic cylinders are located so that the ship can be transported upon a so-called "Fluid Bed". The cylinders are also used to lower the ships on a static support, so that the transfer system with the active elements can be recovered.
