Propulsao

Shuttle Tanker Propulsion

Introduction
Shuttle tankers, which load their cargo from storage facilities at the field or directly from the production platform, are widely used to serve offshore oil fields from which pipeline connections are not feasible. In 1994, for example, just over 50 per cent of the oil brought ashore from Norwegian offshore oil fields was transported by shuttle tankers. MAN B&W Diesel has gained valuable experience in the laying out of propulsion machinery for shuttle tankers by supplying the main engines for all dieselmechanically driven shuttle tankers built with two-stroke main engines during the last decade.

ters to match the above requirements are in operation. The large side thruster power installed on the vessels calls for equipment that can provide sufficient electricity production, i.e. large diesel generators or large shaft generators need to be installed on all shuttle tankers intended for dynamic positioning operation. Consequently, it is often decided to install cargo pumps driven by electric motors. The cargo pumps are primarily used for unloading the cargo in port but may also be used in the field to distribute oil among the segregated cargo tanks. The maximum power consumption of the cargo pumps is typically around 4-5,000 kW. The MCR of the main engine or propulsion motor of a typical 125,000 dwt shuttle tanker is normally between 15,000 and 20,000 kW. The electrical load during steaming is typically around 700-1000 kW and is mainly used to cover the power consumption of the auxiliary equipment related to the ship’s machinery. Estimated average values of the power requirements of a 125,000 dwt shuttle tanker are illustrated in Fig. 1.
Load condition © Propeller load (kW) Electricity production (kW) Time in service (days/year) Sea 15,000 900 140 Port 0 5,500 55 Dynamic positioning 2-4,000 3-6,000 170

Propulsion Machinery
Several different propulsion systems meet the above-mentioned requirements.
• diesel-mechanical