Outrigger Structure for jack-up vessel

The Eager.one team has been working on the design and construction of an impressive outrigger structure. The outrigger will be used on a jack-up vessel offshore Mauritania and Senegal, where the BP’s Greater Tortue Ahmeyim field is being developed. At this field the near-shore hub and terminal marine infrastructure are encompassing berthing facilities for a permanently moored FLNG, the loading of LNG Carriers and an offshore breakwater to shelter those facilities.

For the development of the marine infrastructure of the Tortue LNG hub and terminal a jetty has to be built (see image 1).

Image 1: Marine infrastructure of the Tortue LNG hub and terminal (source: Effiage)

Outrigger structure for pile installation

The jetty will be built on a foundation of piles. The installation of these jetty piles will be executed by the self-elevating platform JB-117 from our client Jack-up Barge (JUB). For the installation, an outrigger is required. Eager.one was asked for the design and construction of the outrigger.

The outrigger structure consists of a rail system and a lattice girder with grippers. It is mounted on a jack-up vessel, making it possible to place multiple foundation piles very accurately from one position. Pile sizes vary between 1830 mm and 2100 mm outside diameter. Total frame size of the outrigger structure is 10.24 m wide, 25.39 m long and 11 m high, with a total weight of 82 tons.

Image 2: The Outrigger Structure

Several Skidding possibilities

The total length of the jetty is significant. Jacking the vessel out of the water and floating to the next pile position for each pile would be very inefficient and time-consuming, and thus expensive. Therefore the outrigger has been designed to skid. First, the outrigger can move back and forth, across the deck. Secondly, the two “arms” can skid alongside the outrigger. With this skidding functionality, it is possible to install multiple piles (with a hammer), from only one jack-position.

The outrigger has now been installed on the self-elevating platform JB-117 and ready for final Site Acceptance Test (SAT). In a few months’ time, the vessel will take off to the Greater Tortue Ahmeyim field.

Commissioning Outrigger

Meanhile, the outrigger structure has been commissioned on board or the self-elevating platform JB-117. During commissioning, the first of the 250 piles have been installed.

Click here to take a look at some of the pictures that have been taken during commissioning.