Rocks & mirror
Encyclopedia of Marine and Energy Technology



Anchor Handling, Tug, Supply Vessel SIEM PEARL, based on Wärtsilä Ship Design’s VS491 CD design, was delivered in 2009 by Kleven Yard in Ulsteinvik (Norway).

Anchor handling equipment consists of a Rolls-Royce Brattvaag 500t covered towing and anchor handling winch of waterfall type with socket compartments and spooling devices. There are four 170m3 chain lockers with a total capacity of 9400m of 76mm chain. Cargo carrying capacities include approximately 3000m3 drill water, 650m3 liquid mud, 650m3brine and 300m3 dry bulk. The aft cargo deck measures 44.5m by 18m providing an 810m2 area capable of accommodating about 1600t of cargo with a deck strength of 10 t/m2. An unique feature is the Triplex MDH gantry crane for safe and man-free anchor handling operations while two U-shaped roll reduction tanks provide a more stable working environment.

The hybrid power plant combines diesel-electric and diesel-mechanical transmission. In combination with selective catalytic reduction and efficient hull design, this resulted in low fuel consumption and minimum exhaust emissions.

The main propulsion is via a twin screw CPP driven by a combination of diesel engines and variable speed electric motors. For each shaftline, one Wärtsilä main diesel engine 16V32 and one electric motor are connected to a Wärtsilä gear. The main engine has a power take off in the front end, driving a shaft generator (3000kW at 720 rpm). With this arrangement the main engine can be used as the propulsion engine at variable speed, the propulsion engine at constant generator speed, or as a generator motor disconnected from the propeller.

The variable speed electric motors have two nominal ratings and speeds. When operating in parallel with the diesel engine the nominal speed is 1370rpm, which is required in order to match the nominal propeller speed of 144rpm. When operating as the only propulsion motor, the nominal speed is 800rpm, equal to a propeller speed of 84rpm. There are also two 2100kW 3516C generator sets and a 425kW emergency/harbour generator.

The Wärtsilä power drive system, based on low voltage 690V/60Hz, eliminates the propulsion transformers used by a traditional 6.6kV/60Hz power drive system. Elimination of the high voltage propulsion transformers gives the following benefits:

- Electrical losses in transformers eliminated (15-20% of total electrical losses),

- Weight and volume of bulky transformers is eliminated,

- Low voltage system makes a more flexible switchboard,

- Centralized location of the vital equipment (in one room) enable easy operation control and maintenance.

Each of the two main 4200mm diameter Wärtsilä Lips CP propellers with HR nozzlesprovides an MCR output of 9500kW. These are supplemented by two 1000kW tunnel thrusters forward, one 830kW retractable azimuthing thruster forward and two 880kW tunnel thrusters aft. This propulsion system gives the vessel a DP2 capability. In addition, two Rolls-Royce high-lift rudders are fitted to enhance manoeuvrability.

Length, oa: 91.00m, Length, bp: 79.35m, Beam, mld: 22.00m, Depth, mld to the main deck: 9.60m, Draught: 7.95m, Max deadweight: 4161dwt, Lightship mass: 6069t, Deck space: 813m2, Deck cargo capacity: 1600t, Output: 2x8000kW + 2x1600kW, Azimuth thruster 830kW, Tunnel thrusters: 2x1000kW, 2x880kW. Speed: 10knt at 12t, 12knt at 18t, 14knt at 32t, 16knt at 60t, 18knt at 72t, Bollard pull: 285-310t.