Pipelayer conversion uses MacGREGOR’s RoRo experience

For a recent pipelayer conversion, MacGREGOR’s RoRo conversion team contributed bow doors, sliding bow cover, pipe hatches and pipe hatch coaming

Last year MacGREGOR participated in an unusual conversion of a panamax bulk carrier to the dynamically-positioned deepsea pipe-laying vessel Audacia for Swiss-based Allseas Group SA. The 225m-long Audacia is suited for the installation of pipelines from 2 inches in diameter up to 60 inches including coating, and is intended for operation in all water depths.

For the project MacGREGOR’s RoRo conversion team supplied lower side-hinged bow doors, an upper side-hinged bow door, a sliding bow cover, side-hinged pipe hatches and the pipe hatch coaming.

“MacGREGOR equipment was chosen for simple commercial and technical considerations; together with its experience in designing specialist systems,” said Roland Bruens, Allseas’ Audacia package manager. “The vessel and MacGREGOR’s equipment are performing as we expected them to; so no unpleasant surprises up to now. We will look forward to dealing with MacGREGOR again on our next newbuild vessel, Pieter Schelte.”

The weathertight lower bow door is located in the firing line tunnel area (about frame 245) and the door, when open, allows the pipe to be passed through. It is supplied with a flat top plate and open web construction.

The door is arranged in two sections, each hinged at the outboard vertical side. Each door leaf opens forward along the longitudinal bulkhead to achieve the required clear opening. Its operation is effected by direct-acting hydraulic cylinders and the operation is controlled from a control station close to the door.

In the closed and open positions, securing the door is by means of hydraulically-operated cleat bolts located in the door. The bolts lock into the ship’s structure and the upper bow door.

The door can be opened in two positions, either fully or partly open. The partly open position will, due to the more exposed position, only be applicable for sea states where no green sea load is present on the door.

The upper bow door is constructed in much the same way, but does not form part of the vessel’s integrity or watertightness. The sliding bow cover is also not part of the vessel’s integrity or watertightness.

The four side-hinging pipe hatches, each comprising one panel, are arranged above the pipehold. The hatch is normally kept open, but is weathertight in the closed position. The rotational movement of the hatches is enabled through hydraulic cylinders attached at the longitudinal coaming. These cylinders are retracted when the hatch is open.

Conversion concept

Allseas is one of the major offshore pipelay and subsea construction companies in the world, and operates six specialised vessels – all designed in-house. Mr Bruens said: “Allseas announced the building of this new pipelay vessel in 2005 because it foresaw that the pipelay market would stay very busy in the upcoming years and that additional capacity would be needed by the company.”

The conversion concept for Audacia was developed in-house by Allseas and undertaken at Keppel Verolme shipyard in The Netherlands. By positioning the stinger – which controls the position of the pipe – on the bow it was possible to use the vessel’s original propulsion configuration.

Mr Bruens highlighted that: “The most novel feature of Audacia’s design is the bow location of the stinger. This design means that distortional effects caused by the conventional requirement to widen and strengthen the aft ship region could be reduced. The bow-side location also ensures smoother water flow off the stern, with consequent improvements in vessel speed. Audacia is able to reach a transit speed of up to 16 knots enabling it to do more work in a calendar year,”

In January, Audacia completed its first assignment, finalising the installation of the L-09 pipeline for Shell UK Ltd. The 16-inch gas export pipeline with double 2-inch chemical injection piggyback pipeline is 19.5km long and is located in the Dutch Continental Shelf of the Southern North Sea. The water depth along the pipelay route varied between approximately 21m and 25m.

MacGREGOR