Special Session: New Deepwater Construction Equipment - A Vision for the Future / Design considerations and equipment details of the 5,000mT Mast Crane of the deepwater pipelay and heavylift vessel Seven Borealis
Authors: Bullock Jackson D. , Seeley Malcolm , Landwehr Marcel , Hughes Paul , Velthoen Gerald 
Published: April 2012

Abstract
The paper will address the application of the 5,000 Te mast crane onboard theSeven Borealis. It's unique design and special features render it a unique toolin deep water construction wherever larger structures are being installed inever deeper water and increasingly hostile environments.
Other than the dedicated heavy lift vessels available in the market, most ofthe SURF construction vessels have limited crane capacities while specializingin installation of SURF product in deep water only. The mast crane onboardSeven Borealis has a capacity normally only found on dedicated heavy liftvessels and combines that with the capability of installing SURF product (rigidpipe, flexible & umbilical's) in deep water. As a result, the mast craneonboard Seven Borealis bridges the gap between SURF installation capabilitiesand heavy lift.
Most cranes having a capacity over 2,000 Te are large derrick cranes. Thispaper will address some of the unique design features of the mast crane onboardSeven Borealis, especially when linked to the S-lay and J-lay systems and usedas a coherent whole operational tool.

Introduction
As the energy market continues to modify relative to the pressures of supplyand demand, contractors are attempting to predict the central specification ofnew assets which will ensure high equipment utilization over the future yearsin a large scale construction project industry. Designing and investing in anasset which will have a life of over 25 years can be as risky as predicting theprice of oil over a similar period of time. Pipelay (and SURF) is a corebusiness of Subsea 7, therefore, vessel concepts for new assets focused onpipelay functionality. Both deep water and shallow water pipelay capabilitiesare part of Subsea 7's current operations and extending the range of assetsengaged in pipelay operations is an ongoing strategic function. Both theatershave unique equipment specialties and the challenge has been to combine all ona single vessel.
With the basic pipelay equipment and ancillary equipment defined, it was clearthat utilization could be increased by considering multi-use concepts oncomponents and addressing extended specifications which would make thesecomponents more suitable for the application desired.
The 5,000 Te Huisman Heavy Lift Mast Crane and its detailed functionalitycomplements the pipelay and subsea construction activities envisioned for theSeven Borealis very well, and in combination with the supporting vesselequipment, provides a unique capability package for the asset.
Subsea 7 has, therefore, created a unique tool for the industry which willallow our clients to capitalize on the multi-facets of the vessel'scapabilities and promote the required utilization needed for Subsea 7'sinvestment.

Design Concept of Seven Borealis
The Seven Borealis1 concept has been derived from Subsea 7's recognition of aneed for a new platform to support the Huisman J-lay system from the AcergyPolaris and a new asset capable of intermediate S-lay capabilities to expandfleet coverage of the market. Although the original concept was not tospecifically combine both functions onboard a single vessel, it soon becameclear that the overlap of auxiliary systems required to support both functions, made for an economical package.