australian marine complex – common user facility floating...

Australian Marine Complex – Common User Facility Floating Dock

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Australian Marine Complex – Common User Facility Floating Dock By Mike Bailey, MSc, C.Eng, MRINA,

David M. Westmore, B.Sc.(Hons), C.Eng., MRINA

Mike Bailey is Director of AMC Management (WA) Pty Ltd responsible for the management of the AMC facilities and the floating dock project on behalf of the West Australian Government

David Westmore is Managing Director of Clark & Standfield, the dock designers. 1. Introduction In the year 2000, the Government of Western Australia commissioned the construction of a new common user fabrication and maintenance facility close to the capital city of Perth and its associated seaport, Fremantle. The purpose of the facility was to enable local industry to target large-scale projects in a number of market sectors and to provide equal access to any company, state, national or international, wishing to undertake such projects in the area. The area housing the facility is known as the Australian Marine Complex and was already home to much of the shipbuilding and repair business in Australia, although docking capacity was restricted to the 8000 tonnes shiplift. This paper looks at the background to the requirements for a floating dock to enhance this capability and how the dock design was evolved to accommodate the requirements. 2. Australian Marine Complex – Common User Facility As part of the Western Australian Government’s strategy to attract industry into the state, the Australian Marine Complex was set up, located south of Fremantle. It is an integrated industrial estate servicing the defence, marine, resource and petroleum sectors with about 100 businesses located there. The Australian Marine Complex incorporates a Common User Facility (CUF) originally constructed with fabrication halls, workers amenities, project offices, wharves, hardstand, cranage, warehousing and reticulated services, covering an area of 40 hectares (approx 100 acres). It is available to multiple users and has injected more than $106million of work into the local economy since its completion in 2003.

By using the CUF, companies can hire the facilities to undertake a particular project thus avoiding the burden of cost associated with creating facilities for projects, which they may not necessarily win or for which they have no requirement when the project is completed.


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Photo 1 - The Australian Marine Complex showing the Common User Facility at the top.

The Royal Australian Navy, in particular, expressed an interest in moving maintenance operations from its base close to the facility with afloat repairs and conversions being transferred to the CUF in 2005. Around the same time, other naval requirements became apparent, particularly the need to refit submarines in a specially constructed maintenance hall.

Photo 2- RAN ANZAC class frigates under maintenance periods at the CUF

Photo 3 - Conversion of a commercial tanker to fleet auxiliary HMAS Sirius completed in 2006

3. Upgrading AMC CUF Facilities The increase in CUF activity led to feasibility studies and business planning for further site developments, which included additional wharfage, power upgrades, dredging and buildings. In addition to these, an increase in docking and launching capacity over the existing 8000 tonnes was considered. Future RAN requirements were key issues for this increase since its West Coast (Indian Ocean) operations have been steadily increasing over the past 15 years. The need for such facilities was considered essential to take account of two major defence programmes:

1) The Australian Submarine Corporation (ASC) was investing $35million in maintenance and upgrade facilities at the AMC to enable it to meet contracts to service the Royal Australian Navy’s Collins-class submarines based at HMAS Stirling. This required the provision of shore transfer facilities at the AMC to move the vessels to a purpose built maintenance hall.


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SUBMARINE HALL

Photo 4 - Submarine Maintenance Hall at the CUF

2) The desire for Western Australia to be in a strong position to bid for the $2billion Amphibious

Ships (LHD) construction and through-life support projects for the Royal Australian Navy. This would require launching and drydocking facilities at the AMC.

An investigation was carried out into graving docks, marine railways, shiplifts and floating docks to provide the drydocking and launching requirements. The floating dock option was found to be the most versatile and cheapest and in 2006 the Western Australian Government decided to proceed with a $174million infrastructure upgrade at the Australian Marine Complex (AMC) in Henderson, which is expected to create up to 3,000 jobs over the next 10 years. It includes the construction of a floating dock, a new transfer system, dredging of a 17m-deep basin to accommodate the floating dock, an extension of the existing eastern wharf, site works and electricity upgrades.

Figure 2 – Proposed Upgraded Common User Facility

According to the WA Government, the investment in the 100m floating dock alone is expected to inject $3billion into Western Australia’s economy over the next 25 years from naval contracts, as well as up to $175million per annum in other projects. In addition, the upgrade would provide the opportunity for WA to bid for a range of other maintenance and construction projects across the marine, defence and resources sectors.


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4. Floating Dock Requirements The floating dock was required to carry out the following primary functions:

1) Land Transfer of 18,000tonne new build LHD For Launching at Quayside level of 3.6m CD 2) Land Transfer of 3500 tonne Submarines and ANZAC Frigates at Quayside Level of 4.3m CD

(now 3.6m CD) 3) Docking of 24000 tonne LHD when complete (without shore transfer) 4) Docking evolutions to be carried out in way of a deep sink basin in the harbour

Whilst the submarine requirements were confirmed with the Australian Submarine Corporation proceeding with the construction of their new facilities, the LHD programme was more problematic – the need for LHD launch facilities would not be known until much later. 5. Floating Dock Concept To meet the requirements, a two-part dock was proposed. One section (Dock 1) would be designed and built to facilitate the docking and land transfer of Collins class submarines whilst the other section (Dock 2) would be designed, but built only in the event of the LHD requirement proceeded.

DOCK 2 = 132000 DOCK 1 = 990001650

232650

LHD = 230000DISPLACEMENT 18000 TONNES

ARLEIGH BURKE CLASS DISPLACEMENT 8500 TONNES

LHD BLOCKING LENGTH 195m

DOCK 1 = 99000DOCK 2 = 132000

ARLEIGH BURKE CLASS

ANZAC CLASS COLLINS CLASS COLLINS CLASSANZAC CLASS

Seaward End Shore End

Figure 3 – Floating Dock and Docked Vessel Combinations

The dimensions of the dock to accommodate the LHD shore transfer at the transfer draft of 4.50m was such that the dock could accommodate Panamax size vessels up to 28000 tonnes when at the conventional docking draft of 5.05m. In addition, dock 2 could accommodate an air warfare destroyer such as the Arleigh Burke Class: one of the vessels being considered by the Royal Australian Navy at the time. Therefore the dock requirements could now be defined in Table 1. As the primary function of the dock was shore transfer, it was envisaged that there would not be a significant amount of onboard ship repair activities. However, in the event that such activities did take place, the power to ships would be provided direct from shore and an existing dockside crane and smaller mobile cranes would provide craneage. To prevent environmental contamination of the dock water during such activities, the dock is provided with a rainwater collection system where contaminated water from the pontoon deck drains to a collection tank via drains located at the end of


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the pontoon deck, one each side, and is then pumped ashore for processing. An upstand at the end of the pontoon deck prevents runoff from the pontoon deck into the dock water.

Floating Dock Configuration Vessels Docking Weight Shore Transfer

Dock 1 Collins Class Submarines Anzac Frigates

3000 3500

Yes Yes

Dock 2 Collins Class Submarines Anzac Frigates Arleigh Burke or Similar

3000 3500 8500

No No No

Dock 1 + 2 (Connected via Splice Plates)

LHD Launch 18000 Yes

Dock 1 + 2 (Connected via Rocking Joint)

LHD Complete Panamax

24000 28000

No No

Table 1 - Principal Requirement for 2 Dock Concept The pontoon deck was kept level without camber for a number of reasons. Firstly, the use of the rainwater collection system necessitated that the dock would always have a trim to facilitate movement of rainwater to the end of the dock where the collection facilities are placed. As a consequence, water would tend to flow along the pontoon deck. Secondly, the level pontoon deck makes it easier to reposition blocking systems without the need to readjust for the dock camber. Thirdly, the deck level would be constant transversely over the dock width with the shore side level during transfers. Finally, the lack of camber simplifies construction. Although the width of dock 1 is large for its length by conventional standards, as it is designed on the combined dock basis, it does provide some additional flexibility for the use of multi hull dockings. This is becoming more important; particularly with one of the local shipbuilding companies undertaking ever larger multihull constructions. Furthermore, the developing oil and gas industry off the West Australian coast will also benefit. Even for mono hulls, the dock is capable of docking more than one vessel transversely. The flying gangways provide access from one sidewall to the other at deep sink but will be in the open position during transfer ashore. Unusually, the flying gangways are also designed to hinge partway back into the dockwell to facilitate access to docked submarines for health and safety. A cross-dock duct is also provided from one sidewall to the other through the ballast tanks. This permits access by personnel as well as for cross-dock cables, utility piping, etc. Many docks have sloping ends to their sidewalls to provide a convenient access route to the top deck as well as saving on steel and pumping. However, because of the need to provide connections between the two docks and the need to provide a grounding point, the end sidewalls were kept rectangular. Access to the dock was therefore by means of outboard stairways from the top deck passing through sally ports in the sidewall to the pontoon deck. 6. Combined Dock Operations Although each dock is capable of independent operation, there will be occasions when the docks are required to operate in combination for larger vessels, typically when the vessel length exceeds 55% of the combined dock length. Two methods are provided for the dock. Method 1 The first method utilises a rocking joint. The Rocking joint consists of six castings on

each sidewall. Three resist shear upwards and three resist shear downwards. The six castings nest into 6 similar castings on the connecting dock opposite and restrain the dock vertically but allow the docks to rotate longitudinally so that no bending moments transfer through the joint. The docks are kept together longitudinally by a connection screw between the two docks.


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ROCKING JOINT CASTING

DOCK CONNECTION SCREW

PONTOON DECK

SIDEWALL – AFT END

Figure 4 - Rocking Joint and Dock Connection Screw On Aft End Sidewall (Port shown, Starboard Similar)

The rocking joint allows the docks to be brought together easily without need for welding etc. Longitudinal bending moments can be carried from one dock to the other through the docked vessel. However, to avoid overstressing the docked ship the longitudinal deflection of the combined docks is monitored with the ballasting arranged to keep the deflection, and hence bending moments in the ship, to the minimum.

Method 2 In the second method, the docks are brought together as in the first method. However, in

this instance, welded steel splice plates are added. The plates on the sidewall are provided with longitudinal stiffeners to increase the compressive buckling capacity of the plates. This is not the situation for the top deck plate due to the smaller gap.

TOP DECK

SPLICE PLATE

INNER SIDEWALL SPLICE PLATES

PONTOON DECK

INNER SIDEWALL

DOCK 2

DOCK 1

TOP DECK

Figure 5 - Splice plates on Top Deck and Inner Sidewall. (Splice plates also provided on outer sidewall and

at pontoon deck level in way of sidewall).

The sidewalls utilise thicker steel in way of the splice plate connections to enable welding/burning off the plates whilst minimising any damage that welding/burning may


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cause to coatings etc. This would only be used for shore transfers with the combined docks. The joint allows the transfer of longitudinal bending moments through the joint thus simplifying the ballasting of the docks during shore transfer.

In order to facilitate control of the combined docks, an additional control console is provided in dock 1 to control and monitor dock 2. 7. Shore Transfer 7.1 Transfer System The dock was originally designed for a rail transfer system, which requires a high degree of accuracy in aligning the dock rails to the shore rails. To facilitate this, the dock was provided with a number of features:

1) a centring spigot on the shore end of the dock centreline was provided to locate into a shore receptacle to align the dock rail centreline to the shore rail centreline.

2) The grounding cylinders extend into the grounding pads to keep the dock centreline parallel with the rails

3) The grounding cylinders could be raised or lowered to accommodate dock transverse deflections under load to ensure transfer level accuracy.

4) The grounding cylinders were capable of accommodating mooring loads and the motive force of the vessel transfer carriage.

Photo 5 – Scheuerle SPMT transferring a submarine at Fincantieri, Italy

Eventually it was decided to use SPMT modular transporters as the transfer carriage, as this provided additional capability to the marine complex for moving heavy loads, including non dock use, and increased the flexibility of the dock’s transfer position. The SPMT modular transporters carriages also have the capability of accommodating local variations in ground level up to ±350 mm.


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As a consequence, the centring spigot was removed and the grounding cylinders were only required to provide a bearing load to maintain a constant level for transfer. The system also meant that the dock did not have to be aligned to a rail system allowing the dock transfer location to be moved slightly to reduce the amount of civil works. 7.2 Ballasting Arrangements The principle of ballasting the dock is to minimise longitudinal deflections and bending moments by ensuring that the net loading on each section of the dock is minimised. Thus for a section, the sum of dock weight, ship weight, and ballast water should be as near as possible equal to the displacement of that section. This applies to both normal docking evolutions and shore transfers. The technique is often called differential ballasting and is used for all large docks to avoid excessive longitudinal strength requirements.

SHIP WEIGHT DISTRIBUTION OVER BLOCKS

Figure 6 – Differential Ballasting to match ship Weight Distribution over Blocks

Normally, where a dock is used in tidal areas, the ballasting of the dock needs to take account of both tidal movement and vessel loading. In these circumstances, it can be simpler for the side tanks to compensate for change in displacement due to tide changes and the pontoon tanks to compensate for vessel loading. However, although the tidal range at the AMC is in the order of 1.1m, the tides are Diurnal and often fairly static throughout the day. This meant that large and/or fast tidal changes would not occur and therefore a conventional ballast arrangement could be used without the need for tanks specifically for tidal compensation – small changes could be easily dealt with using a conventional dock ballasting arrangement. The dewatering speed governs the maximum speed, V, at which a vessel can be transferred onto the dock, i.e. V = Q/DL where Q is the pump capacity and DL is the uniformly distributed load of the vessel. This gives the transfer rates set out in Table 2.

Vessel Distributed Load Pumping Rate Transfer Speed Transfer Time

Submarine 69 t/m 148 t/min 0.13 km/hr ¾ Hour

LHD 150 t/m 148 t/min 0.06 km/hr 4½ Hours

Table 2 – Transfer Speeds and Times


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7.3 Transfer Procedure The general procedure for transfer onto dock is:

Step 1 – Dock is raised approximately 300mm higher than the required transfer level and manoeuvred into position. The dock is held in position by the mooring lines.

Step 2 – Dock uniformly ballasted until grounding cylinders touch grounding pads. Minor cylinder adjustment, if required, to ensure correct dock level.

Step 3 – The shore end ballast tanks are further ballasted until a load of approximately 500 tonnes is shared between the cylinders. This ensures that the dock is properly grounded and fixed vertically in line with the shore levels

Step 4 - As the vessel is manoeuvred onto the dock, the ballast tanks under the load are deballasted to provide lift equivalent to the ship load to be supported.

Step 5 – As the vessel moves further on, additional ballast tanks are deballasted ensuring that the lift per tank group matches the ship load per tank group along the dock length.

Step 6 – When the vessel is in the undocking position, the shore end ballast tank group is deballasted until grounding reaction is zero.

Step 7 – Dock raised 300mm clear of grounding pads and manoeuvred to deep sink basin During the transfer procedure the ballast in the shore end tank is adjusted to maintain the required bearing load ensuring consistency of support. Once the dock has reached the deep sink basin, normal docking evolution procedures apply.


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7.4 Grounding System Although some docks are completely free floating for land transfer, it is often the practise to ground the dock to ensure accuracy of dock levels. This can be in the form of an underwater grid as used by Bath Iron Works floating dock where the dock is grounded over its full length or by the use of docking ledge/lip where the dock is grounded only at the shore end. It was decided to adopt the latter methodology with the sidewalls being extended to bear down on the quayside. This gave accuracy of levels but minimised the amount of civil works required. To ensure the dock remains at a constant level during the transfer operation, the dock is provided with 4 hydraulic cylinders under the sidewall extensions at the forward end of the dock. These bear on steel plates embedded in the shoreside pavement. The hydraulic cylinders are in line with the outer and inner sidewalls and to ensure that the loads are equally distributed between the inner and outer sidewalls they are cross connected. The cylinders have the capability of extending/retracting to adjust the dock level. This was primarily to compensate for transverse deflections of the dock pontoon when using a rail system, but still useful for levelling the dock transversely and vertically. They also ensure equal distribution of load between the inner and outer sidewall. The system is designed for a combined nominal load of 500 tonnes but will accommodate loads up to 2000 tonnes. The dock is ballasted until it is level whilst providing a bearing load of 500 tonnes. These loads are then monitored throughout the transfer process with the ballasting being adjusted to maintain a constant bearing load. In addition, the load between one side and the other can be monitored to ensure that the dock’s transverse ballast distribution is not creating any heeling moments (Note: when free floating, this is ensured by correcting dock heel)

PORTABLE ROADWAY LEVEL WITH QUAY

QUAYSIDE

GROUNDING PADS

EXTENSION PIECE

HYDRAULIC CYLINDERS

SIDEWALL

Figure 7 - Grounding System Arrangement

Two transfer locations were considered, one for the submarine transfer and one for the LHD transfer. The height of the hydraulic cylinders were governed by the LHD transfer as the dock was required to be at a lower level to give greater draft and hence lift. For the submarine location, the dock would float at a higher level since a lesser lift/draft was required and the reduced draft also reduced dredging works in way of the transfer quay. This necessitated a removable extension piece to be provided to compensate for the higher level of the dock, rather than building up the height of the grounding pads, in order to provide a clear jetty area.


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7.5 Dock Depth and Shore Levels The pontoon depth of the dock is normally selected to give the required lift capacity at working draft and for transverse strength. In this case additional needs were:

1. Submarine Transfer: Draft to give 69t/m lift at minimum tide height 2. LHD transfer: Draft to give 150t/m lift at minimum tide height 3. Minimum Freeboard of 300mm when at maximum tide during transfer

The sidewall depth was selected to ensure that the minimum freeboard was not less than 2000mm when the dock is at deep sink. Although various authorities permit lower freeboards down to 1000mm, the value selected was considered more appropriate for this size of dock. The depth of water is based upon the height of the vessel above the pontoon, which is a function of the dock level relative to the ship level ashore, the ships docking draft and a clearance between the blocks and keel of not less than 600mm The resulting levels on Dock 1 are shown in figure 8.

2900

5500Min Transfer Draft

490

29002900

1500

Max Ballast Level

Land Level +3.6m CD

-3.39m Chart Datum

MHHW +1.1m CD

Chart DatumMin Transfer Draft

Max Deep Sink

10710

5500

490 2010

2900

1404

5354

2000

510

17700

16700

Estimated

ROADWAY

Figure 8 - Dock 1 Transfer and Water Levels

8. Structure 8.1 General Arrangement Since dock 1 and dock 2 are required to operate as a single dock, each dock was kept dimensionally the same in transverse section and the same structural configuration used in both. Longitudinally, the docks were the same except that dock 2 had 2 additional tank groups although all tank groups in both docks were the same individual length of 16.500m.

Photo 6 & 7 - Example of Floating Dock with Similar Structural Configuration to the AMC Dock Under Construction.

The dock structure is designed to the Classification Society Rules of Bureau Veritas for Floating Docks (Ref 1). The structure consists of a series of transverse bulkheads evenly distributed over the dock length.


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The docks structure was therefore designed on the basis of operating together with the exception that longitudinal strength, due to the rocking joint, was designed on the basis of an individual dock. Bureau Veritas rules define the minimum longitudinal strength based upon the dock/ship length and the lifting capacity. However, in the design of the splice plates, the longitudinal strength of the combined docks was investigated by simulating the land transfer of the LHD on to the dock and examining the loadings across the joint between the two docks.

THIS SECTION

SAFETY DECK

TOP DECK (PLATING REMOVED)

CENTRELINE WT BULKHEAD

INTERMEDIATE LONGITUDINAL WT BULKHEAD

TRV WT BULKHEAD

TRV NWT BULKHEAD PONTOON DECK PLATING REMOVED

Figure 9 - Typical Structural Section of the AMC Floating Dock

8.2 Vessel Loadings The various combinations of ship and dock resulted in the following loadings:

Dock Configuration Vessel Lift

Distributed Lift Dock Draft

Land Transfer

Dock 1 Max Theoretical 12000t 180 t/m 5.05m No

Dock 1 Submarine 3500t 69 t/m 2.90m Yes

Dock 2 Max Theoretical 16000t 180 t/m 5.05m No

Dock 1 + 2 LHD 18000t 150 t/m 4.50m Yes

Dock 1 + 2 Panamax 28000t 180 t/m 5.05m No

Table 3 - Vessel Loadings

The keel blocks to support these loadings were designed for a standard spacing of 1650mm whereas the bilge/side blocks were designed for support on the transverses spaced 3300mm apart. The Keel blocks had a nominal capacity of 350t each and the bilge blocks 250t each.


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A pair of longitudinal girders are provided either side of the centreline for the purpose of accommodating the submarine cradle, which uses a 3.6m spacing, at any position along the dock. 8.3 Hydrostatic Loading The longitudinal loadings of the dock are controlled by the use of differential ballasting. I.e., the ballast in the tanks will be at various levels, see figure 6. These differences result in hydrostatic loadings on the transverse bulkheads. Similarly, differences in ballast levels transversely can cause hydrostatic loadings on the longitudinal bulkheads although generally, the ballast levels transversely are fairly uniform. Thus the bulkheads are designed to accommodate sufficient differences to permit operation both during normal docking evolutions and transfer operations. For the dock, this has been taken as 4.4m. The outer tank boundaries are subject to the difference between the dockwater level and the ballast level, see figure 10. Whereas conventional ship design requires tank boundaries to be designed to the maximum hydrostatic head measured from the overflow point, the dock’s tank boundaries are based upon the differences between water levels during normal operation. For example, a dock would not be sunk with a tank kept dry. This approach, which is standard in dock design, can reduce the loadings on the bulkheads in the order of 60% compared with a ship design approach with consequent saving on steel and cost. To prevent over sinking of the dock beyond the deep immersion waterline (set at 2m sidewall freeboard) the dock uses an air cushion where air trapped in the sidewall compresses until equilibrium is reached. The depth of the air cushion is controlled by the depth of the air pipe below the safety deck and is set during the deep sink trials. The consequence of this is that the safety deck requires being air/watertight and the structure capable of accepting a hydrostatic head equal to the height of the dock waterline above the ballast level. 9. Dock Manoeuvring To avoid the need for deepwater at the quaysides and the implications this has on the civil works, it was decided to dredge a basin in the harbour of the common user facility where the dock could be sunk to her maximum depth. The dock is manoeuvred from her lay up berth to the basin for docking evolutions, and then to the transfer quay by means of a number of mooring winches. The system will be automatic using a joystick control. At the quayside the mooring winches will be used to hold the dock onto the quayside for the transfer with some supplementary mooring lines. A study was carried out to assess the capability of the dock with a docked vessel to be manoeuvred between the deep sink basin, lay-up berth and transfer quay for the weather conditions with wind speeds up to 12.8 m/s. The position of the mooring wire anchor points was constrained by the need to provide accessible positions at the quayside. The resulting analysis confirmed the proposed configuration and winch capacities

Figure 10 – Hydrostatic Loads, H


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DEEP SINK BASIN

SHORE TRANSFER QUAY

LAY UP BERTH

SHIP REPAIR BERTH

Figure 11 – Dock 1 Mooring and manoeuvring

10. Power The dock is provided with onboard generators in the starboard sidewall and standby generator in the port sidewall. This enables power to be provided throughout manoeuvring the dock, carrying out docking evolutions in way of the deep sink basin and also the ballasting during land transfer. When the dock is at the lay up berth shore power is provided for periods of lay up and in the event the dock is used for ship repair.

AUXILIARY SWITCHBOARD DOCK SERVICES 240 1ph 50Hz

DOCK SERVICES 440v 3ph 50Hz

EMERGENCY GENERATOR

G

REPAIR STAT IONS 3 OFF (P&S) 415v 3ph 50Hz 240v 1ph 50Hz

MAIN SWITCHBOARD MAIN GENERATOR

G DOCK SERVICES 240v 1ph 50Hz

DOCK SERVICES 440v 3ph 50Hz

YARD SUBSTATION

SHORE FEEDERS

FWD

DOCK 1 - PORT SIDEWALL

DOCK 1 - STARBOARD SIDEWALL

DOCK 2 FEEDER

G

PRIMARY CROSS DOCK CABLE

AUXILIARY CROSS DOCK CABLE

Figure 12 - Power System Schematic for Dock 1

11. Main Pumping System The lifting and sinking of the dock is undertaken by the main dewatering system. Large centrifugal pumps located in the pontoon are used to deballast the dock, whereas ballasting is by means of free flooding. In addition to normal docking evolutions, the dock dewatering system is also required to facilitate the land transfer of ships.


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Figure 13 - Diagram of dewatering system on Dock 1

The size and quantity of pumps were based upon the need to provide a reasonable transfer speed for shore transfer when using only two pumps and the need to provide a reasonable lifting time when operating all pumps. This resulted in the following capability:

Number of pumps Total Pump Rate Notes

Combined Docks

Normal Docking 8 592 tonnes/min Lift a 28,000 vessel in 2 hours

Land Transfer 2 148 tonnes/min LHD (150 t/m) transfer speed 0.06km/hr

Dock 1

Normal Docking 4 296 tonnes/min Lift a 12,000 vessel in 2 hours

Normal Docking 4 296 tonnes/min Lift a 3,500 vessel in 1 hour

Land Transfer 2 148 tonnes/min Submarine (69 t/m) transfer speed 0.13km/hr

Table 4 - Pumping Capability The above pumping times are based upon achieving a working pontoon deck freeboard of 450mm. During the early stages before a vessel has sued, the lifting rate is very high due to the small waterplane of the sidewalls. Slower pumping rates are required in these circumstances, particularly during suing as well as when ballast tank levels are low to avoid suction loss. It was found that variable speed pumps would be problematic in providing reduced pumping rates and as a consequence it was decided that ‘throttling’ of the compartment valves would be a better approach to reduce flow rate and hence speed. The compartment valves are thus capable of 25%, 50%, 75% and 100% opening. A non-return valve is provided on the discharge side of the pump to prevent backflow acting on the pump (causing the motor to act as generator) and outboard of this is the main hull valve for the discharge. There are twice as many inlets to the discharges, the primary reason being to increase the flooding rate under low head conditions as can occur during land transfers.


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Each ballast tank compartment is separated from the dockwater by two valves; a main hull valve and a compartment valve. The main valves (Inlet and Discharge) are of the screw down type gate valve operated by electric motor actuators with handwheel for manual backup. The compartment valves are of the vertical sliding gate type operated via reach rods by an electro-pneumatic press in the safety deck. The valves are failsafe in that loss of electrical or air supplies results in the valve failing shut. Closing weights are provided to assist in closing the valve. In addition, the electro-pneumatic press can be operated locally, and in the event of loss of electrical supply/signal, air pressure can be used to raise the valve. If there is no air pressure, the valve can be raised or lowered manually using a handwheel. The valve control compressed air system is designed to permit the cycling of all valves twice per minute. The object of the system was to ensure that in the event of power/air failure, the dock would immediately stop in a safe condition without the need to manually close a multitude of valves – a lengthy period during which the dock could develop dangerous trim, heel, or deflections. During dewatering it is common practise to open the main discharge valves and with the pumps running continuously, control the dock by opening and closing the compartment valves. A similar arrangement applies during flooding using the main inlet valves and compartment valves.

MAIN INLET VALVE COMPARTMENT

VALVE

MAIN DISCHARGE VALVE

Figure 14 - Typical Arrangement of Dewatering System Valves and Pumps The dock is provided with a control system capable of automatic, semi automatic and manual operation. Sensors monitor dock draft, heel, trim, longitudinal deflection, tank levels, and, when in shore transfer mode, the grounding loads. These are processed to control the opening and closing of the dock dewatering system valves.


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12. Current Status At the time of writing, the construction of the amphibious vessels (LHDs) is now being undertaken outside Western Australia. Although there is now no urgent need for the 2nd dock, it remains a future development possibility for the docking of larger vessels up to panamax size. Strategic Marine won the contract for the construction and delivery of the floating dock and is currently building the hull (pontoon and sidewall to safety deck) in their facilities in Vietnam. The dock will then be towed to the AMC where the sidewall and outfitting will be carried out. 13. Conclusion The floating dock concept involving the linking of two docks and the ability to transfer vessels ashore demonstrates the great versatility of the floating dock. Advantage of this flexibility has already been demonstrated by the fact that the project could proceed whilst the amphibious (LHD) warship programme remained unknown with the construction of dock 1. The dock provides a platform for land transfers and has the future capability for a second dock to be added to create a combined dock capable of accommodating vessels up to panamax size. The dock features several unusual requirements, such as the ability to manoeuvre, offload and maintain trim to very tight tolerances. Whilst none of the solutions to achieve the requirements are new, it is rare to see these within a single platform. The ability to achieve the design intent places a strong focus on the control system, which allows for automatic, semi-automatic and manual control. Whilst using technology that has been used in previous dock designs, it will be configured around the specific needs of our dock and an appropriate balance between “tried and tested” and “state-of-the-art” has been found. The build strategy is also a balance in several ways:- • Design was taken to a class-approved status, rather than reliance on a performance specification,

in order to fully define the end-product. Detailed engineering only has been undertaken by the builder

• A turnkey contract was awarded and, although a major emphasis was placed on local content, the builder had considerable freedom in how this was achieved. In the event, the heavier steelwork was fabricated overseas, with the systems engineering, installation and commissioning being performed in Australia.

• A block construction and assembly method is being used to maximize time under-cover.

• Being a Government contract, local content was maximize whilst continuing to draw on international expertise which was typified by:-

− A British dock designer

− An American Control Systems designer and integrator

− German pumps

− An Australian prime contractor

− A Vietnamese fabrication subcontractor

14. References 1. Floating Dock, Rule Note NR475 DTM R00 E, published by Bureau Veritas, October 2001


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15. Appendices 15.1 Principal Particulars

Dock 1 Dock 2 Combined

Dimension

Length over Pontoon 99.00m 132.00m 232.65m

Width of dock 53.00m 53.00m 53.00m

Width between sidewalls 44.00m 44.00m 44.00m

Clear width of entrance between fenders 41.80m 41.80m 41.80m

Depth of pontoon at centre line 5.50m 5.50m 5.50m

Depth of pontoon at inner sidewall 5.50m 5.50m 5.50m

Length of sidewall 102.30m 132.00m 235.95m

Height of sidewall above pontoon at inner sidewall 13.20m 13.20m 13.20m

Depth of tween deck space 5.95m 5.95m 5.95m

Width of sidewalls 4.50m 4.50m 4.50m

Height of keel blocks (conventional dockings) 2.00m 2.00m 2.00m

Maximum Draft over keel Blocks 9.20m 9.20m 9.20m

Corresponding freeboard of sidewalls 2.00m 2.00m 2.00m

Minimum depth of water required at site 17.70m 17.70m 17.70m

Lifting Capacity

Working Draft 5.05m 5.05m 5.05m

Maximum Lift at Working Draft 12000t 16000t 28000t

Maximum Distributed Load at Working Draft 180 t/m 180 t/m 180 t/m

Transfer Capacity

Maximum Distributed Load at Transfer Draft = 2.90m 69 t/m - -

Maximum Distributed Load at Transfer Draft = 4.50m - - 150 t/m

Dewatering System

Number of Dewatering Pumps 4 4 8

Dewatering Pump Capacity (per pump) 74 t/min 74 t/min 74 t/min


Page 19

15.1 General Arrangement

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Page 20

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