Catamaran gantry crane for engineering procurement construction installation contract

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1 The IES Journal Part A: Civil & Structural Engineering ISSN: (Print) (Online) Journal homepage: Catamaran gantry crane for engineering procurement construction installation contract Bob L.Y. Cheung To cite this article: Bob L.Y. Cheung (2010) Catamaran gantry crane for engineering procurement construction installation contract, The IES Journal Part A: Civil & Structural Engineering, 3:4, , DOI: / To link to this article: Published online: 20 Oct Submit your article to this journal Article views: 1364 Citing articles: 2 View citing articles Full Terms & Conditions of access and use can be found at

2 The IES Journal Part A: Civil & Structural Engineering Vol. 3, No. 4, November 2010, TECHNICAL PAPER Catamaran gantry crane for engineering procurement construction installation contract Bob L.Y. Cheung* Bob Cheung Offshore Consultants Private Ltd., 38 Toh Tuck Road, #06-01, Singapore , Singapore (Received 22 June 2010; final version received 7 September 2010) The objective of this article is to introduce a new piece of multi-purpose and cost-effective offshore installation equipment suitable for onshore fabrication work, shallow water oil and gas field development and wind turbine installation. Shallow water shall mean less than 100 m in this context. The equipment can also be used in the disused platform removal market, which will become a multi-billion dollars offshore business in the near future. The equipment has a special feature: it can be used to loadout a deck from the fabrication yard onto a material barge for towing to site, install the deck, then remove a disused deck and offload it from a material barge back to the yard for rework. With a simple modification, it can install wind turbine and minimal platform. Creating a sustainable business for the equipment is a key consideration. Keywords: EPCI; catamaran float-over gantry crane 1. Introduction In terms of overall project cost, engineering procurement construction installation (EPCI) contracting strategy is the most cost-effective method to develop oil and gas fields. It can also reduce the Field Operator s in-house project cost by deploying only one Project Management Team (PMT) to oversee the whole job at a few locations. The reasoning is that a truly EPCI contractor can do almost everything inhouse and their in-house engineering design team is in the best position to know their preferred method of fabrication and installation, hence their fit-forpurpose design can be tailored to suit the company in reducing fabrication and installation costs. This is a win-win situation for all parties. Unfortunately, it may be due to lopsided contractual Terms and Conditions, huge project cost and financial risk and project liabilities, not many contractors are willing to venture into solo EPCI business. Thus, there are less than a handful of truly EPCI contractors in the world today, willing and able to execute this kind of turnkey projects. Many recent EPCI contracts in this region were won by Joint Venture (JV) companies. The JV entity may consist of several engineering firms: one doing the platform design and one handling the pipeline and subsea scope, several fabricators: one doing the jacket and one responsible for the deck and an installation contractor doing all the offshore work. Each party is carrying his own risk and liabilities with lots of qualifications. However, in reality, it is extremely difficult, if not impossible, to manage a huge project with so many parties. Problems will always occur at the interface scope. This type of consortium is unlikely to produce a cost-effective solution, because every partner, as it should be, is looking after his own scope of work, schedule and lump sum. No one is looking at the big picture to produce a win-win situation for all. This kind of JV-EPCI contracting strategy does not seem to produce the cheapest solution for the owner and the Field Operator. The objective of this article is to consider the whole project cost and propose a few innovative ideas to make EPCI projects better integrated and more cost-effective, especially for shallow oil and gas field developments in South East Asia. The article will cover the following. (1) Propose a piece of new installation equipment to cut installation cost for small wellhead decks and medium size production decks. (2) Propose a few practical deck design guidelines to ensure that the deck will fit the new installation equipment and reduce fabrication cost. This is to provide a greater project cost reduction. (3) To make the equipment more versatile to handle other types of work such as disused platform removal, wind turbine installation and minimal platform installation. With more flexible lifting arrangements, this equipment can also handle brown-field modification projects making it a more sustainable business. * bob.cheung@rocketmail.com ISSN print/issn online Ó 2010 The Institution of Engineers, Singapore DOI: /

3 258 B.L.Y. Cheung 2. Historical review on offshore installation Design of offshore platform, both jacket and topside, is always location-specific and installation equipment dependent. A piece of heavy lift equipment may be readily available and competitive in the North Sea, but may not be suitable for small field development in South East Asia due to high day-rate and high mobilisation and de-mobilisation costs. Therefore, a competitive design must be based on what is available in the local market. In the early 1970s, one could hardly find a derrick barge able to lift more than 2000 tons. Therefore, all the heavy decks in the North Sea and elsewhere were designed as multiple topside modules. Each module is designed to perform certain type of function such as utility module, compression module, electrical module and drilling module, and they are usually supported on top of a module support frame (MSF). In some cases, the MSF is so heavy that it has to be lifted in several pieces and welded together offshore. Each module is then lifted onto the MSF and skidded into position by jacks mounted on top of the MSF. Perfect fit-up is not achievable. The task of connecting all the cables, piping runs and structural members between modules is time consuming. This kind of offshore hook-up and platform commissioning will take many days, if not months, to complete, keeping in mind that offshore labour rates are much higher than onshore rates. Other major project expenditure is the cost to provide accommodation for few hundred offshore hook-up personnel to work on a big deck. This type of offshore piecemeal construction method is extremely uneconomical, but it was the standard field development method for the past few decades. In the early 1980s, with the appearance of heavy lift vessels (HLV), such as the Saipem 7000, Heerema s Balder and Thialf and McDermott s 101, the North Sea offshore market benefited greatly. Offshore installation contractor (OIC) can now offer alternative methods to cut cost and reduce both hook-up duration and steel tonnage. However, a large part of the savings will go to the installation contractor to pay for his huge equipment investment. The day-rate for this type of vessel is expensive. For smaller oil field development in South East Asia, the use of this type of HLV is economically unjustified. Therefore, nothing much has changed in South East Asia. Even today, it is still difficult to find a derrick barge to lift a deck over 1500 tons at a reasonable day-rate. To save cost, we may have to consider multiple lifts or putting equipment on separate skids for lifting, instead of mobilising a big derrick barge outside of the region. In the early 2000s, an age-old installation method was rediscovered. This was the Floatover Installation Method. This method can be traced back to the huge concrete gravity platform era in the North Sea in the 1970s, where all the heavy topsides were installed by multi-barge floatover technique. The difference between the old method and the present day method is that the old method was always carried out in sheltered water, whereas the present day floatover is done in the open sea. This sounds difficult, but in real life, the allowable wave height for open sea floatover operation is very small. However, major design problems will arise during transportation and mating operations. No matter whether it is a single hull floatover barge for internal floatover or a catamaran floatover vessel for external floatover, the vessel must be checked for large environmental forces during tow. For internal floatover, the motion induced mating force is a major design consideration. So far, no more than 15 heavy decks have been installed using single barge internal floatover method in this region. Recent projects included the PTTEP Arthit PP topside (17,500 tons) in the Gulf of Thailand in 2008 (Tan et al. 2008), and the ConocoPhillips North Belut CPP deck (14,000 tons) in Indonesia in For external floatover, only one project in South East Asia has been reported. It was the Murphy Oil Kikeh topside (3500 tons) for a Spar platform, installed in 2006 (Edelson et al. 2008). In recent years, oil field development concept, especially in South East Asia, has changed due to availability of jack-up drilling rigs, FPSOs and FSOs. Field operator prefers light weight wellhead platforms for drilling and a FPSO for oil processing, because there is no upfront payment for the FPSO, which will improve the cash-flow situation. The rental rate for the FPSO is on day-rate basis after the first-oil date. This kind of wellhead platform is much lighter than before, since the drilling loads, such as hook load and set-back load, are no longer carried by the deck. They are supported by the jack-up rig. However, if the wellstream composition requires complicated processing equipment, super heavy decks will still be needed. In many recent field developments, the jacket has been installed prior to the completion of the deck fabrication. This is to match their drilling schedule as a jackup drilling rig must be booked months in advance. It is the change of the field development strategy in recent years that makes this new installation equipment very cost-effective for small deck installation. It should be noted that the equipment is not only for small oil and gas field developments. It can work for major fields also, such as the Arthit and Bongkot gas fields in Thailand and the Block B gas field development in Vietnam. Each field will need more than 100 wellhead platforms over the development period, and the saving from this installation equipment for small deck installations will be very large indeed.

4 The IES Journal Part A: Civil & Structural Engineering Comparison of floatover installation methods In South East Asia, there are many smaller and marginal oil and gas fields in shallow water. In this article, shallow water shall mean less than 100 m. Most of the wellhead decks, designed for this kind of field development, weigh approximately 1500 tons. Traditionally, wellhead deck installation is by lifting using a derrick barge. Unfortunately, not many derrick barges in the region can lift more than 1500 tons and one has to pay expensive mobilisation charges to bring a big derrick barge to this region. One should also keep in mind that at a practical lifting radius directly above the centre of gravity of the deck, the lifting capacity may drop by 20% or more, and a large capacity derrick barge may become the critical equipment for a project. This article proposes a new piece of installation equipment using external floatover concept and strand jacks to overcome this lifting limitation at a much lower cost. Floatover installation can be classified into two types, external and internal floatover. The most common method is internal floatover using a single hull barge for both transportation and floatover operations. Many field operators consider this method to be less risky for transportation, but it comes with a huge cost. This additional cost could be due to the following factors. (1) Finding a strong barge to carry a heavy deck in South East Asia is not easy. Usually, a strong barge has to be brought in from outside the region. In few cases, a special transportation barge, called T-barge, has to be modified or built for a particular internal floatover operation. (2) All the internal legs of a standard jacket have to be removed to provide a big slot to accommodate the floatover barge for internal floatover, and the outer legs must be designed to take the berthing load, which could be few thousand tons. It needs lots of extra steel for this installation load case. (3) Instead of designing a deck with usual deck leg spacing, say m, it may end up with a deck spanning more than 40 m between supports due to the big slot opening. The cost penalty is due to additional steel to cater for the large span. (4) To accomplish internal floatover, a support frame for loadout and floatover is necessary. The frame could easily weigh more than 1000 tons. For a wellhead deck, internal floatover installation is physically not practical due to space limitation. The best solution is to go for external floatover and the extra cost is much lower. To address the field operator s concern about deck transportation for external floatover installation, a less risky transportation method would be to transport the deck(s) on one barge and the equipment on a catamaran barge. 4. Design requirements for the catamaran gantry crane To develop a new piece of installation equipment on a long-term commercial basis, we should develop a sustainable business model. The new installation equipment must be multi-purpose and versatile to cater for many types of projects, and must be designed to fulfil the following operation requirements. Since most of the wellhead decks will weigh about 1500 tons, and it would suggest that a 2000 tons design capacity would be sufficient for the South East Asia wellhead deck installation market. However, this equipment can be used for the platform removal market and a 3000 tons design limit would be necessary to cover the older type of wellhead deck structures Loadout consideration Many existing fabrication yards in the region do not have a strong skidway or bulkhead to loadout heavy structure, say over 3000 tons. This new gantry crane should be designed to alleviate the problem without incurring huge financial cost to the yards. This means that we should use the new gantry crane and existing yard facilities to loadout a heavy deck without expensive upgrade, if possible Transportation consideration The new gantry crane will be designed and classed by a certification authority for restricted ocean tow without cargo. Restricting the operating area will greatly reduce the investment cost. The deck will be transported on a separate barge, and this arrangement will satisfy field operator s requirement Offshore floatover-lift installation The new catamaran shall have, as a minimum, an eight points mooring system and be able to lift a deck, up to 3000 tons. It must stay within the specified vessel excursion limit. This is to ensure the catamaran will not impact the jacket. Under the usual sea states for lifting operation, the expected excursion should be less than 1 m Disused platform removal Within certain dimensional constraints, this gantry crane can remove disused deck in one piece and send it

5 260 B.L.Y. Cheung back to shore for reconditioning and reuse. If greater height is needed, the gantry crane can be modified to suit Wind turbine installation With small modification to the gantry crane, it will be able to install wind turbine. However, wind turbines have to be transported on a separate material barge. The design sea states for the installation condition will need to be raised to cater for the high wind offshore area Minimal platform installation If the minimal platform is a monopod, it will be similar to a wind turbine. For marginal field development, this gantry crane can install the whole minimal platform in one piece. However, pile installation is another major issue. Figure 1. Catamaran floating gantry sitting on land. 5. The solution: catamaran floating gantry crane The catamaran floating gantry is not a new concept. A piece of the equipment was first built for the construction of the I-205 Columbia River Bridge (Bittner 1980). Since then, three other similar equipments have been fabricated and commercially available in the market; the Versabar s Bottom Feeder gantry crane used mainly for deck salvage projects, the Ballast Nedam s 8700 tons lift capacity catamaran crane, Svanen, used mainly for bridge construction and wind turbine installation and Scaldis catamaran twin shear-leg crane, Rambiz, used for bridge construction and wind turbine installation. Every piece of the equipment is designed for a particular function and is not for multi-purpose construction and installation. The proposed installation equipment, that will satisfy both the operation and design requirements, would be a gantry crane mounted on two barges. This is a catamaran floating gantry crane (see Figures 1 and 2), which can work both on-land and offshore. When it is placed on-land and on skidways, it can function as a gantry crane, doing almost all the jobs that a landbased gantry can do as well as it can act as a loadout carrier gantry to spread out the load on the ground during loadout. This is to safeguard against soil and bulkhead failure. When it is mounted on two barges, it is a catamaran able to perform floatover lifting of a deck structure. For the disused platform removal market, it can remove a disused deck in one piece and send it to shore for refurbishment and reuse, thereby creating a secondhand offshore platform market. With a simple modification, it can be used to install wind turbine and minimal platform. Figure 2. barges. Catamaran floating gantry mounted on two 5.1. Design considerations Loadout design consideration It is straightforward to loadout a heavy deck, if the yard has a strong skidway system and a strong bulkhead (see Figure 3) (Cheung and Gho 2002, Cheung and Foong 2008). What we need is a detailed loadout procedure, strong loadout shoes, high-capacity ballast pumps, winches and a strong barge. However, if the existing bulkhead is not strong enough, then the catamaran floating gantry could offer an alternative solution, provided the load is not excessive. In any loadout operation, we have to consider the following design conditions (1) Soil bearing capacity failure: This is due to excessive soil pessure. In order to overcome the problem, we may use multi-wheel transporters or longer loadout shoes to spread out the load on the ground. If the load is too high, we will have to rely on skidways. However, we cannot assume the lengthened loadout shoe can produce uniformly distributed load on the

6 The IES Journal Part A: Civil & Structural Engineering 261 Figure 3. Loadout of a heavy deck using loadout shoes on skidways. ground as the shoe is not infinitely rigid, and there is a limit on how far the load can be spread. The best way to spread out the load is to use more shoes. For example, consider a 2000-ton four-leg wellhead deck structure and assuming that each leg can carry 500 tons. If the standard loadout shoe is 6 m by 1 m, then the ground pressure is 83.3 tons/m 2 (see Figure 4). If we were to use the catamaran floating gantry crane (see Figure 5), each leg will be supported by four loadout shoes, and if each shoe is 6 m by 1m, then the ground pressure is 20.8 tons/m 2. This is a great reduction and soil failure may be avoided (see Figures 4 and 5). If the loading is too large, we may have to go for double skidways per leg. Nowadays, we can perform very detailed loadout analysis, taking into consideration nonlinear soil stiffness, structural-pile-water-barge interaction and barge flexibilty, to obtain more accurate result due to interaction and load redistribution. This will help us make an informed decision to reduce the over-conservatism in the design, which is necessary if we do not have a complete loading picture. (2) Bulkhead failure: When the deck travels across the bulkhead, the load from the leg, acting on the bulkhead at the quayside, could vary a great deal depending on the control of ballast water in the barge during loadout. This massive load could fail the bulkhead and overstressing the structure. To overcome this problem, one Figure 4. Deck loadout using four loadout shoes sitting on two skidways. could build a strong skidway to bridge across the bulkhead sheet piles or use the catamaran gantry crane to reduce the load on the bulkhead. (3) Slip circle failure: This type of failure is common when the surcharge load is too high. One solution is to use the catamaran gantry crane to spread out the surcharge load or build a load-relieved platform to transfer the surcharge load to the ground using deeper penetration piles. Another innovative solution is to redesign the sheet-pile and tie-back system to mobilise more soil area to resist slip circle failure.

7 262 B.L.Y. Cheung Transportation design consideration After a deck is loaded out, it will be transported on a single barge and the gantry crane will travel on a catamaran. As it can be seen in Figures 6 8, the gantry crane sits on top of four pyramid shoes, which will be welded to the barge deck during transportation and mating. During transportation, forces and moments will be generated at the contact points between the gantry crane and the pyramid shoes, and hinges will be provided at the support points to relieve the moments due to roll, pitch and yawn. An onshore gantry is really a portal frame with pin supports at the base. The mechanism to prevent collapse due to side wind load is the rigid connection at one of the top corner of the portal frame. In the present design (see Figure 7), the leg of the floating gantry crane is relatively short, may be just half of the height of an onshore gantry. This means that this gantry is much more robust to resist the greatly reduced sway end-moment due to shorter leg height, and we do have rigid knee-braced connection at both top corners of the portal frame. However, a model test will be required to confirm the design and its sea-keeping capability for a particular operating area. This equipment is not designed for worldwide operation and ocean tow. Therefore, the investment cost will be much cheaper Floatover lifting consideration The principle of floatover is to control the ballast of the transportation vessel to do the mating. This leads to several design issues. (1) Barge-Jacket clearance: For internal floatover, the gap separating the barge and the jacket is very tight, and the jacket legs will act as barge bumpers to take the impact load. For external floatover, the gap between the two barges, as in the present catamaran design, is more than Figure 5. Deck loadout using 16 loadout shoes sitting on 4 skidways. Figure 7. Fixed upper gantry crane. Figure 6. gantry. Perspective view of the Catamaran floating Figure 8. shown). Pyramid support shoe (Skid shoes are not

8 The IES Journal Part A: Civil & Structural Engineering m and impact load does not exist, as long as we can control the anchor lines. The gap is dictated by what is the commonly available barge size in the market. The barge is to transport the deck for mating. (2) Floatover-loadout frame: For external floatover, the frame is not necessary, if the deck was loaded out using the floating gantry. Once it is on the transportation barge, it can be set at the correct elevation using simple supporting stools. Correct elevation should be about 1 2 m above pile cut-off elevation at top of jacket, and this is to minimise the lowering distance. If the deck was loaded out on skid shoes, we can adjust the height before loadout. (3) Lifting: There are four lifting points on the gantry. The actual positions can be adjusted before loadout. Once fixed for a particular job, they should not be changed on site. A typical dimension could be 12 m 6 12 m or 17 m 6 15 m rectangular configuration. To meet other odd deck sizes, a spreader frame can be used as a transition frame. The anchor heads for the strand jacks can be fixed at the deck lifting padeye locations, while the cylinders will be housed in the gantry. If the total lowering height is limited to less than 1 2 m, the whole mating operation could be over within few hours. installation. However, we need a small derrick/utility barge to install the piles, risers and pipelines. The dayrate for the small barge is cheap Operation procedure Figures show the entire floatover-lift operation Cost estimate The weight of the floating gantry is about 2500 tons based on the required lift weight of 3000 tons. The gantry is made up mostly of 1000 mm diameter tubular members and the depth of the truss is almost 20 m. Including the cost for four sets of cable jacks, on rental basis, fixed inside the gantry, spreader frame for lifting, four big winches capable of holding eight point mooring lines in 100 m of water depth, power generators and sufficient number of very high capacity pumps to lower the deck onto the pile, the total cost is estimated to be about US$20 m. The cost could be Disused platform removal consideration Disused platform removal is the reversed operation of installation. As long as the wellhead deck can fit inside the gantry, it can be lifted in one piece. However, we may need a spreader frame and link plates to match the disused deck padeye locations. If a greater height is needed, we can modify the pyramid shoes. Figure 9. Wind turbine installation Wind turbine installation consideration For wind turbine installation, the gantry crane can be placed on one barge (see Figure 9), and a special lifting frame is welded to one end of the gantry. Two gripping clamps, similar to riser clamp, can be fitted on the lifting frame for the pickup-and-set operations using strand jacks or winches (see Figure 9). It is assumed that the turbine is sitting on top of a pre-installed supporting structure with all the subsea cables already in position Minimal platform installation consideration Minimal platform is similar to a monopod. In this case, the installation will be similar to wind turbine Figure 10. (Step 1) Tow catamaran to site location, run mooring lines.

9 264 B.L.Y. Cheung Figure 11. (Step 2) Set up the catamaran enclosing the jacket between two barges. Ensure catamaran excursion is within the allowable limit. Figure 14. (Step 5) Pick up the deck to clear top of pile cutoff. The clearance should not be more than 300 mm. Figure 12. (Step 3) Using tug boats and winches to bring the deck transportation barge into the catamaran. Bumper guides would be installed to reduce impact load. Figure 15. (Step 6) Move out the deck transportation barge and move the catamaran forward to set the deck. Risers and pipelines will be installed by a pipelay or utility barge. add the cost for renting two barges for the catamaran, one material barge for the deck and miscellaneous items, one accommodation vessel to house people including construction staff, welders, company representatives and subcontractor personnel and one marine spread for handling anchors and barge movement. With all the above costs, one can work out the barge day-rate. This should be much cheaper than a derrick barge day-rate. To build a new 1500-ton derrick barge, the present cost could be over US$100 m. Figure 13. (Step 4) Position the deck under the gantry. Connect anchor heads from the strand jacks to the deck lifting eyes. higher if we were to allow for back-up equipment. The pumps will work in conjunction with the strand jacks to reduce the mating time. On top of this, one has to 6. Deck design to suit gantry dimension To have a better chance of winning an EPCI contract, the offered price must be competitive, if not the lowest. Therefore, we should design the deck to suit the new installation equipment and the fabrication procedure to cut cost. The deck should be designed to suit all the dimensional constraints, such as width, height

10 The IES Journal Part A: Civil & Structural Engineering 265 limitations and padeye locations of the installation equipment. Deck leg spacing should be kept between 12 and 15m in both the long and short directions to make sure the spanning primary deck beams, with fabricated reinforcing haunches if necessary (see Figure 16), can be purchased from the market without fabricating heavy plate girders. The deck beams should be overlaid on top of the primary haunch beams (see Figure 16), and they should be selected from a single beam size to avoid splicing and load bearing stiffener fabrication. Load bearing stiffener will take longer time for tight fitting and welding. Different beam heights can be adjusted using shim plates. Deck plate shear stiffness should be considered in the design to avoid the need for sway bracings. Deck lifting eyes should line up with the strand jack positions on the gantry as much as possible. If offset cannot be avoided, one will use spreader frame for the load transition. Equipment layout and conductor spacing must suit these restrictions. It should be noted that an open deck is more flexible for equipment layout than a close deck. If this can be done, the fabrication rate for the deck could be greatly reduced and the bid price can be much lower (see Figures 16 18). Figure 16. Cellar deck fabrications with overlaid W24 deck beams sitting on top of the W36 haunch beams. Figure 17. flexibility. Open cellar deck fabrication for an eight-leg deck structure weighing 1600 tons. Note the equipment layout

11 266 B.L.Y. Cheung Figure 18. Main and cellar deck of an eight-leg deck structure in final stage of fabrication. Typical primary deck beam, spanning between the deck legs, can be made of W36 beam with fabricated end-haunches. Based on experience, this should be able to carry the usual uniform area loading for a standard wellhead deck or a small size production deck. Deck beams could be W24 with no need for load bearing stiffeners at the beam-to-beam intersections. Edge beam is a channel section for easy fitting and welding. In offshore fabrication, to achieve low fabrication hours, we should avoid cut-and-cop details and make loadpaths as simple as possible. We have to balance the design between labour cost and material cost. For example, we can reduce the deck beam (W24) span by introducing additional internal supports, then the W24 beams can be sized down, the overall weight may be slightly reduced, but the labour cost could be a lot more due to additional painting, cutting, welding, fitting-up and handling activities in the yard. If a yard has invested heavily in modern equipment and has many expat staff, it will surely increase the yard overhead and it will be reflected in the labour hourly rates. The design team must balance these two factors, labour and material, to come up with a cheap fit-for-purpose design and at the same time, make it easy to be installed by the new catamaran gantry crane (Cheung 1993). An open deck will provide maximum space usage and make it easier for arranging piping runs and cables. This is another cost increased factor. The same concept can be applied to four-leg, six-leg or eight-leg deck structures. After fabrication, the loadout gantry can straddle the deck in the long direction for lifted-loadout if needed. Once loaded out, tiedown can begin and ready for tow. For eight-leg deck, we may use two gantry cranes for loadout. Concluding remarks The proposed catamaran gantry is useful and versatile, but most importantly, it can offer a much more competitive pricing in a standalone bid. If we were able to design a deck to suit both fabrication and installation, then we should have a good chance of winning EPCI projects. References Bittner, R.B., Substructure construction methods I-205 Columbia river bridge. ASCE Convention & Exposition Portland, April Cheung, L.Y., Design economics of connection details for offshore wellhead structures. Journal of the Institute of Engineers, Singapore, 33, Cheung, L.Y. and Foong, K.G., Design considerations of a loadout skid frame for a 14,000-ton upper hull structure. The IES Journal Part A: Civil & Structural Engineering, l (1), Cheung, L.Y. and Gho, W.M., Effect of soil-structurebarge interaction for loadout analysis of offshore steel jackets. Journal of the Institute of Engineers, Singapore, 42, Edelson, D., et al., Kikeh development: spar floatover installation. Offshore Technology Conference, Houston, 2008, Paper no. OTC Tan, B., et al., Arthit field development: float-over hardware design and issues. Offshore Technology Conference, Houston, 2008, Paper no. OTC