Offshore Mooring

Site details

Block B8/32 Benchamas Field


Gulf of Thailand

Water depth:

71m (233 ft.)


Q2 2018


The Benchamas Explorer Floating Storage and Offloading (FSO), owned and operated by Chevron, was installed in 1999. Chevron decided to replace the existing aging FSO with a new FSO provided by MISC – FSO Benchamas 2 (BFSO2). BFSO2 is a converted vessel using an Aframax sized crude oil tanker. The build took place at MMHE shipyard in Malaysia. BFSO 2 is turret moored at the same location to the existing mooring system and piles.


Below are the major challenges occurred during planning and operation stage:

1) Field Shut down period The tow could not be on critical path, so all procedures and contingencies were to be in place to avoid any schedule delay.

2) Fishtailing As BFSO2 is a converted from tanker, the hull form was not designed to tow from stern but due to constraints and limitations, this became the only option which resulted in various unfavorable outcomes, including fishtailing. The tow speed may need to be reduced, causing significant impact on the schedule.

3) BFSO 2 readiness There was a delay in sail away causing a domino effect for the mobilization.

4) Additional award of scopes The additional scope to the base case contract at the tail end of the project caused a strain on our resource utilization as we had a shorter time to deliver.

5) Multiple Marine Inspection and approval OVID, MOFT/MWS Survey and Chevron’s MSRE inspection and approvals for the marine spread demanded significant man-hours which had to be allocated during onshore phase to attain approvals for the marine spread.

6) Change in Survey Contractor Changes in Thai importation policy resulted in us having to take on another contractor with approved clearances 2 weeks before sail away.

7) LRAD and Security Personnel Mobilization The requirement for security had to be adjusted between our client and our end client.


  • Project management, engineering and manpower for the tow of the BFSO2 from the shipyard to field
  • Charter of 2 Anchor Handling Tug Supply (AHTS) for station keeping for the hook-up
  • Engineering and analysis to the Offshore Installation Contractor (Solstad) to support the hook-up of the FSO and installation of riser system
  • Provision of an integrated security plan for the tow with security equipment and security personnel


Main Tow – AHTS: POSH Salviceroy & POSH Salvigilant

Harbour tugs: KSP Solar, KST Success, Maju Sun & Maju Scorpius


1) Field Shut down period InterMoor worked very closely with Client and subcontractor to make sure the FSO was prepared for the tow (installation of towing gears, navigation signals, survey system setup, permits and clearances, tow inspection checklist completion etc.) prior to the sail away date. With effective communication and reporting system, client and subcontractors were constantly updated on the scheduled vs actual progress. A detailed tow plan with contingencies and mitigations was prepared and discussed during HAZID, pre-job meeting and several other meetings for respective parties to have a clear understanding of scope and responsibility.

2) Fishtailing A careful and extensive planning was carried out to mitigate the effect of fishtailing on the towing operation and schedule. a. Bollard pull calculation A contingency for fishtailing was included in the bollard pull calculation b. Parallel tow arrangement The initial plan was to use two towing vessels with one towing the FSO (bridle arrangement) and other one as escort vessel. After discussion with towing vessel suppliers and Tow Masters it was decided that a parallel configuration was more suitable. c. Trim by turret of FSO FSO was trim 1.7m by turret to reduce the fishtail effect. d. Provision of harbour tugs from MMHE yard to Horsburgh Typically harbour tugs are disconnected once the tow reaches eastern buoy (Johor OPL); however, to control the stern of the FSO until it passed the Singapore straits, two of the harbour tugs remain connected at stern till Horsburgh lighthouse. e. Towing in slack tide in Singapore Straits Arrangements were made with Johor Port for the FSO to be towed in slack tide during daylight with reduced oncoming traffic. f. Apply grease hourly to minimize chain chafing The FSO did fishtail during the tow. However, with above procedure in place, the FSO tow was completed in five days with an average tow speed of 5.5 knots, leaving two days for CIQ and handover process.

3) BFSO 2 readiness The notification from the client about the delayed sail away date was immediately communicated to all subcontractors to minimize the impact.

4) Change in survey subcontractor The new contractor had the required permit in place for clearing survey equipment in and out of Thailand. The equipment mobilized and installed on time on both FSO and Tow vessels without affecting the project schedule.

5) Station Keeping for BFSO1 disconnection Based on the station keeping analysis of BFSO1 for mooring line disconnection, it was suggested to the client to cut the mooring lines by alternate mooring sequence instead of cutting them by cluster. This will reduce the bollard pull requirement. This resulted in some significant improvement from the proposed method and was adopted in the revised operation procedure.


The work was completed on time, without interruption of production, and without any lost time incidents.