Installation of the Horn Mountain Spar Using the Enhanced DCV Balder
Authors: Dijkhuizen Cees , Coppens Ton , van der Graaf Peter 
Published: October 2008

Abstract
During the second quarter of 2002 Heerema Marine Contractors (HMC) installed the Horn Mountain Dry Tree Spar facility [ref.1], using its recently enhanced Deepwater Construction Vessel (DCV) Balder. This paper describes the most important issues of this marine installation project, including methodologies specifically developed to suit the capabilities of DCV Balder. Such features include the Worlds largest diameter Mooring Line Deployment winch and the dual crane lifting of the Spar Deck.

Introduction
In the late nineties of the last century major oil companies, driven by portfolio considerations and the depletion of their easily accessible reservoirs, extended their exploration activities more and more into deeper water offshore areas. As a specialized marine contractor, in order to adapt to these and future needs of operators, HMC's strategy to approach this market was based on:To remain a "Marine Contractor providing a range of solutions" with extended capability to offer the full range of its customer's future deep water needs.Maximizing and leveraging HMC's core expertise, assets and corporate values.Maintaining the highest priority on robust and safe offshore methodologies. As a result of this analysis and after extensive discussions with oil companies, the decision was taken to convert the Semi Submersible Crane Vessel (SSCV) Balder into the Deepwater Construction Vessel (DCV) Balder.
Features of the DCV Balder such as the Dynamic Positioning (DP) system, the 1050mT capacity J-lay system and the world's largest Mooring Line Deployment winch, the Crane traction deepwater lowering winches in combination with its existing large heavy lifting capacity results in the following main benefits:The ability to use one vessel to execute all marine installation works for a complete Deepwater Field Architecture, thereby eliminating interface risks and multiple mobilization charges.The adaptability to change mode of operations to execute combined scopes of work such as pipelay, mooring line deployment, heavy dual crane lifting and subsea installation. DCV Balder is presently committed for the BP Southern Green Canyon/Mississippi Canyon Deepwater development in the Gulf of Mexico.
Recently completed projects include the pre-lay of the Nakika FPS Moorings and installation of the BP Horn Mountain Spar. The use of DCV Balder enhanced capabilities, the revised working practices adopted by HMC and HMC's Quality, Environment, Safety and Health (QESH) Management System applied on BP Horn Mountain project will be described in this paper.

Dcv Balder Capabilities
DCV Balder (Fig.1) was built as Semi-Submersible Crane Vessel (SSCV) in 1978 and underwent an extensive life time extension and conversion program in 2001 [ref.2, 3, and 4]. The characteristics of the vessel are shown in table 1.
Of prime importance for deepwater installation is the Dynamic Positioning (DP) capability. The DCV Balder was equipped in 2001 with seven new 3500 kW thrusters resulting in a total thrust capability of 350mT, allowing the vessel to keep position in more than 40 knot winds in DP Class 3 condition and to hold large horizontal pipelay tensions.