Initial Design of Offshore Floating Marina System H. Chung* T. W. Oh* S. Namgoong* S. B. Kim* C. H. Jo** *Ocean Space Inc., Seoul, Korea **Naval Architecture and Ocean Engineering Dept., Inha University, Incheon, Korea
Abstract Marinas are often located in prime port side locations. In Korea these locations are already developed and reclamation of the existing properties poses many difficulties difficulties and financial overhead. overhead. Also, to develop a standard marina in Korea with tide ranges up to 8 meters would require considerable dredging and reclamation works needing long lead times and large SOC costs. The offshore floating marina system is an independent floating static level system that does not require fixed location breakwaters. The entire marina floats with the tide giving a calm consistent berthing condition for vessels irrespective of the surrounding tide and weather conditions. The floating marina system provides also for all of functions needed to marina comprising a breakwater to protect the vessels, the pontoon system to house the vessels, a club house and retail tourism precinct, fuel reservoir and associated support facilities in a turn key self contained unit. The modular nature of the system will mean that initial demand can be met with simple units and then further modules can be added quite easily without the related expansion d ifficulties or infrastructure. This paper contains the main characteristics of the floating marina system and the design process. The mooring, motion and stability analysis, the overall & local structural design and the mooring & anchor system design are briefly introduced.
Key Words:
Floating Marina System, Offshore Floating Structure, Mooring & Anchor Design
1. Introduction In Korea, the interest in marine sports and leisure is rapidly growing. Therefore, the demands of marina facilities are also increasing with the increase of the number of yachts and pleasure boats. Marina is defined as facility for mooring of yachts and boats. Existing marinas are mainly located at shoreline, therefore, in order to build a new marina, lots of problems related to site selection, local interest groups, environmental concerns, SOC investment requirements etc. are raised from the initial stage of the development.
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The floating marina system is different from existing marinas in concept. This is a completely independent offshore system and it can provide breakwater in itself by locating mooring boats inside the floating structure. This system also absorbs the large tidal variation effect characteristic in the west coast of Korean Peninsula. The entire marina support facilities can be installed at the upper deck and available spaces inside the pontoon. In this paper, we introduce initial design of the floating marina system, its main facilities, the mooring, motion & structural analysis results and the anchoring system design.
2. Main Characteristics of Offshore Floating Marina System The floating marina was designed to have a capacity of 200 berths in one unit and, based on the market condition, to increase the berthing capacity by installing the additional units to the side of previous units. To define the waterspace area of marina, boat mix should be determined first based on demand analysis. Boat mix of 200 berth is determined as shown on Table 1 referring to the Japanese marina cases because the social trend of Japan is similar similar to Korea. Table 1. Boat Mix (200 Berth) Boat Length
Number of Berths
32ft
48
34ft
8
42ft
72
44ft
8
52ft
56
59ft
8
Total
200
In one side of the waterspace, berths of dingy class yachts are arranged, and the other side, berths of cruiser class boats are located considering the different demand of boating market. Based on the arrangement of
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berths, mooring facilities, fairway, turning basin and channel width are decided as Fig. 1. The whole area of the required waterspace is calculated as 56,000 ㎡.
The area and volume of inner facilities are decided considering the maximum usage plan on a daily basis as sho wn on Table 3. Table 3. Marina Inner Facilities Facility Power House Fuel Storage System Sewage Disposal System Water Supply & Storage System Ballast Seawater System Boiler Room Warehouse
Area(㎡) 3,500 4,000 3,000 4,500 48,000 2,400 2,400
Volume(㎥) 12,120 28,000 21,000 31,500 240,000 19,200 16,800
The draught and freeboard height of marina was decided considering the maximum wave height, the minimum required pontoon depth, floating structure motion behavior and the deck wetness probabilities. The fairway depth of marina entrance was decided considering the vertical motion of the floating structure and the draught & motion effect of yachts together. The main dimension of the floating marina system is shown on Table 4 and the bird’s eye view of marina is shown on Fig. 2. Table 4. Main Dimension of 200 Berth Floating Marina
Fig. 1 Fairway, Turning Area and Berth Arrangement
Length
400m
For the upper deck facilities to support marina activities, the required area is calculated and arranged based on the existing marina study in Japan and UK as shown on Table 2.
Breadth
400m
Freeboard
4.5m
Draft
4.0m
Table 2. Floating Marina Upper deck Facilities
Center of Gravity
3.09m
Center of Buoyancy
1.5m
Facility
Area(㎡)
Storage and Repair
2,400
GM
Marina Support
3,500
Displacement
460,000ton
Recreation Center
4,500
Concrete Hull Weight
280,000ton
Lecture Room Shower and Management Management Building Shopping Center
500 1,000 400 1,000
Lavatory & Shower Room
600
Lodging Accommodation
2,000
Observation Tower Club House Meeting Place Heliport
200 1,000 600 1,000
Because the offshore floating marina system is an independent structure away from the coast, it needs its own utility facilities such as fuel storage tank, power room, sewage disposal system, water storage tanks, ballast seawater tanks etc. These facilities are located inside floating concrete pontoons. The concrete hull consists of outer and inner side spaces with watertight bulkheads. The ballast tanks are located along outer hull side and the other facilities at inner hull side with double bulkheads for safety consideration during accidental events like collisions with o ther ships.
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Fig. 2 Offshore Floating Marina Plan (200 Berth)
3. Offshore Floating Marina Design 3.1 Structural Type and Material Selection The factors regarding location of marina, sea state, weather conditions and seabed conditions should be considered to decide the type of
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structure. The expected location of the floating marina has a depth of 20-30m and the large tidal variation of 8 m. The pontoon type has a lot of construction experiences in Korea and its wave response motion can be minimized by the size and shape control. Also, the construction cost is cheaper than other types of floating structure available in offshore market for a depth of 20-30m. The offshore floating marina uses concrete as a primary material for pontoon structure due to anti-corrosion and durability effect. Steel will be used for upper deck facilities considering its relative weight advantage.
3.2 Mooring and Motion Analysis Stability, motion and mooring analysis is carried out to check the adequacy and safety of the integrated pontoon and mooring system. For the stability analysis in intact and damaged conditions as shown on Fig. 3, all the weights of upper deck and inside pontoons are calculated and LCG, VCG and corresponding draft to all loading conditions are computed based on the weight distribution.
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Case 1
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frequency, dynamic motion, lateral pressure and stability of the floating structure.
3.3 Hull Structure Design Hull structure design was performed by the global strength analysis and the local stress check for construction joints, mooring connectors and so on. In offshore structure, fatigue failure should be checked also for longterm wave stresses. In global strength analysis, the stress and displacement of the entire floating structure was calculated with full weight distribution and maximum mooring loads during storm. The structural analysis has been performed for the critical sagging & hogging as shown on Fig. 4, the mooring, Fig. 5, the slamming, Fig. 6, the sloshing and the twisting conditions. In the sagging & hogging condition check, the pressure distribution under the bottom plate for the storm condition was estimated. The offshore floating marina is consisted of rectangular concrete beams, columns, slabs and walls. The applied loads for global strength check are self weights, upper deck facility loads, inside pontoon facility loads, live loads and mooring loads. It was estimated that the marina hull structure has enough strength for all the applied loading conditions.
3 4 6
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9
Case 3
5
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9
Case 4
Fig. 3 Assumed Hull Flooding Area for Damaged Condition The complete time domain mooring and motion analysis with 3-D diffraction and radiation method was performed for the hull modeled by panel elements. The significant and most probable extreme motions and accelerations are computed for 50-year return period environmental conditions as shown on Table 5. Table 5. 50-Year Environmental Design Condition Wind Current Wave Velocity Velocity (m/s) (m/s) Height(m) Period(sec) 45.0 1.6 5.5 9.0
Fig. 4 Displacement & Stress Results for Sagging & Hogging Condition
Water Depth (m) 20.0
Deck wetness, slamming and sloshing possibility in storm condition exists during the life of floating marina. Also, it is required to check the secondary disturbance effect inside marina for the protection of mooring yachts during storm case. The probability of deck wetness and slamming is calculated by reviewing the heave motion that is the largest effect among six degrees of freedom of motion for the floating marina. The result is that it has some probabilities of slamming and deck wetness, therefore, they were checked in detail in hull structure design. Sloshing is the phenomenon that tank fluids move with the motion of floating structure. It should be considered for the check of natural
Fig. 5 Displacement & Stress Results for Mooring Condition
Fig. 6 Stress Results for Slamming Condition
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The local stress check was performed with shipwreck loads for the underwater passage structure connecting two pontoon marinas and for the piers of shuttle ferry boat with ship impact loads as shown on Fig. 7 and Fig. 8 respectively. Guide Frame
Fig. 10 Dolphin Jacket Side View The mooring & anchor system consists of jacket dolphin, the guide frame connecting dolphin to marina hull and the joint connector between dolphin and guide frame as shown on Fig. 11. The jacket dolphin should have proper strength to endure large horizontal mooring loads as checked in Fig. 12. The guide frame fixed by anchor bolts to the concrete hull was designed by steel section as shown on Fig. 13. The wearing material called ‘bushing’ is used for the protection of joint connecting structure. It prevents the damage of guide frame by friction forces and reduces friction noise during heave motion of marina hull.
Fig. 7 Stress Results for Underwater Passage Structure
Fig. 8 Stress Results for Pier Structure of Shuttle Ferry Boat Fatigue loads in stress concentrated joints due to repetitive waves during the entire life of floating marina were checked for mooring connectors in dolphin anchor system as below Fig. 9.
Fig. 11 Dolphin Jacket System
Fig. 9 Fatigue Stress Results for Mooring Connector
3.4 Mooring & Anchor System Design The selection of mooring equipment and facilities mainly depends on environmental conditions, size and shape of floating structure, water depth, sea bottom topography and soil properties. The dolphin mooring system is adopted for the floating marina because of large tidal variation effect characteristic in the west coast of Korean Peninsula as shown on Fig. 10. The basic concept of the mooring & anchor system is to design the component as simple as possible, to transfer mooring forces effectively to anchor system and to minimize friction forces generated from vertical motions of large tidal variations. Also, the design should be economic and efficient type in construction aspect and easily repaired or replaced during operation and maintenance period.
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Fig. 12 Stress Results of Structural Analysis of Dolphin Jacket
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References
Dolphin Pile
Fig. 13 Guide Frame & Anchoring Connector Design The maximum mooring forces for the design of dolphin anchor was determined by 50-year return period environmental condition as shown on Table 5. The maximum anchor force exerted by the marina structure is about 3,200 ton with appropriate safety factor. The total 10 dolphin jackets are arranged on both sides of marina hull to sustain the mooring loads as shown on Fig. 14.
D1
D2
D3
D4
D5
Dolphin Jacket
ABS (2003) “Guide For the Fatigue Assessment of Offshore Structures” ACI State of the Art Report (1985) “Offshore Concrete Structure for the Arctic”, Concrete International, pp.23 ∼33. API Recommended Practice (2000) “2A-WSD twenty-first Edition”. Berne (1992) “Floating Concrete Structures” VSL International Ltd Bhattacharjee, Garrett, Sweetman, (1997) “Mobil tackles Floating LNG Challenges”, Mobil Technology Co. Offshore Engineer. British Standard (1980) “Steel, Concrete and Composite Bridges Code of Practice for Fatigue” BS 5400: Part 10. DNV Recommended Practice C203 (2001) “Fatigue Strength Analysis of Offshore Steel Structures” Horiba, Inoue, Kobayashi, Shuku, Simamune (2001) “Overview of Mega-Float and Its Utilization”, Mitsubishi Heavy Industries, Ltd., Technical Review Vol.38 No.2, pp.39∼46 Kinney, Schulz, Spring (1997), “Floating LNG Plant will stress Reliability and Safety”, Mobil Technology Co., World Oil, Vol. 218, Issue 7, pp. 81~85. Owen. F. Hughes (1983) “Ship Structural Design: A Rationally Based Computer Aided Optimization Approach”. John Wiley & Sons Inc. Remmers. G, Robert. Z, Paul. P, Robert. T(1998) “Mobile Offshore Base: Proceedings of the Eighth International Offshore and Polar Engineering Conference”, Vol. 1, pp 1~5. The Center for Marine and Petroleum Technology (1998) “Floating Structures: a Guide for Design and Analysis”, Oilfield Publications, Vol. II.
Fairway
Fairway
Dolphin Jacket D6
D7
D8
D9
D10
Fig. 14 Dolphin Jacket Arrangement of Floating Marina System
4. Conclusion In this paper, the initial design of offshore floating marina is briefly introduced. The primary hull sizing, the required waterspace and facilities of floating marina of 200 berths were established. The main characteristic of the marina is the concrete pontoon-type having mooring basin at the center of floating structure. The stability, motion and mooring analysis were performed for the integrated hull and mooring system. The global hull strength and the local stress in important connecting parts were verified for the safety of floating structure in operational and survival conditions. The mooring and anchor system is selected and designed as dolphin jacket system with anchoring connector and guide frame to overcome the large tidal range in Korean coast. Afterwards, the construction and installation methods of the floating marina and the operation and maintenance plan in normal and emergency cases will be developed. This work has been carried out with assistance of Ministry of Maritime Affairs and Fisheries of Korea and Ko rea Maritime Institute.
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