Two Platform Supply Vessels (PSVs) and one multi-functional Offshore Vessel (OSV) with Voith Schneider Propellers will enter service in the North Sea over
the next two years. Each of these special ships for the oil and gas industry will
be installed with two Voith Schneider Propellers (VSP). Unlike the two 278-ft. ships with identical design, the third one, measuring over 305 ft. in length, will be additionally fitted with a moonpool. This allows launching the on-board submarine robots. They carry out control and repair jobs at extreme water depths.
The three vessels are owned by the Norwegian shipowner Østensjø AS. The two 279.5 ft. PSVs with a width of 63 ft. and a draft of 21.3 ft. are currently being built at the Spanish shipyard Astilleros Gondan. On each them two VSPs type 32R5 EC/300-2 will be installed, designed for an output of 2,500 kW, so that each of the two PSVs has an overall propulsion power of 5,000 kW.
The drive concept is diesel-electric. The VSPs are driven by an electric motor. The electric energy
is provided by diesel generators. As a result, the diesel engine can be utilized more efficiently. For the ships in question, which will be operated in varying conditions, this concept is advantageous, as it generates merely the amount of energy that is actually needed. This results in lower fuel and maintenance cost for the operator.
The two PSVs will be used for supplying oil platforms. Solid cargo is being stowed on deck. Liquid cargo such as methanol is carried in special tanks. The OSVs also take effluent water, drilling mud and waste from the oil platforms onshore where it is disposed of in an environmentally friendly manner.
With an overall length of 306.4 ft. and a width of 65.6 ft. (draft 6 meters), the third OSV, also referred to as ROV (Remote-Operated Vehicle – Support and Survey Vessel) is fitted with high-tech appliances. At its center is the so-called moonpool, a weather protected alternative for launching sub-marine equipment. With this equipment, even extreme drilling depths that are beyond the Ultra-Deep-Drilling rate of approximately 6,561 ft., can be reached.
The submarine equipment is used for control and repair jobs at pipelines and offshore systems. This OSV operates with two VSPs type 36R6 EC/300-2 with a total output of 7600 kW. These VSPs, too, are driven diesel-electrically. Another special feature of the vessel that is currently being built at the Norwegian shipyard Karmsund Maritime Service AS, is its sailing speed of 18 knots – quite high for a vessel with VSP propulsion. The two smaller PSVs are capable of 15.5 knots.
The drive concept of Voith Schneider Propellers is ideal for Platform Supply Vessels, as the ships are unloaded and loaded on the open sea, even in rough conditions. This requires a high degree of maneuverability of the vessel, keeping the risk of a collision between ship and offshore platform at a minimum. Roll damping is another key feature of the VSP. During standstill and slow speed the VSPs, thanks to their short steering time, can be used to reduce the effects of high seas on the ship. In this case, the VSPs, fitted with VRS roll stabilization, generate a counter moment to the wave moment. As a result, 80 to 90 percent of the rolling motion of the ship can be suppressed.
Rolling motions are ship movements that result in fast acceleration of a ship. They impair the safety of working on deck and may cause sea-sickness even among experienced crew. The combination of Voith Schneider Propeller and Voith Roll Stabilization thus greatly enhances the application window of OSVs and allows working on deck even in bad weather conditions. The ensuing cost advantage for the shipowner is obvious.