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Appendix D

Types of Construction Vessels and Equipment

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Types of construction vessels and equipmentIn the following examples are given of vessel types and construction equipment

that may be applied for the installation of the BalticPipe offshore pipeline. The

vessels shown are only indicative of vessel types and may differ depending onselected installation contractor as well as special requirements identified during the

planning and detailed design phase.

Survey veselsFor the summer 2000 geotechnical and geophysical survey a ship similar to the

vessel shown in Figure 1 was used.

Figure 1 Survey vessel for geotechnical and geophysical survey (Geoconsult

Geograf)

Figure 2 Typical near-shore survey vessels

For the surveys to be carried out during the construction phase, two main types of

survey vessels will likely be used depending on availability and suitability.

For the near-shore survey activities the limited depth calls for small survey vessels

similar to vessels shown in Figure 2.

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For survey of the central offshore sections larger vessels, 50-80 m of length are

typically employed. Examples are shown in Figure 3.

Figure 3 Example of offshore survey vessels used for construction support

DredgingDredging in the near-shore areas may be performed using a cutter suction dredger

as shown in Figure 4.

Figure 4 Example of cutter suction dredging equipment showing close-up

of cutter head on the left

For shallow water depths a conventional backhoe placed on a barge may be

applied as shown in Figure 5.

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Figure 5 Example of barge equipped with back-hoe for near-shore

dredging works

For pre-trenching in deep waters on locations with hard seabed, a trailer suction

hopper dredger specially modified for hard soil conditions may be used. Example

of trailer suction hopper dredger is shown in Figure 6.

Figure 6 Example of large trailing suction hopper dredger vessel capable of

dredging in water depths down to 75 m

PipelayPipelay vessels may be positioned by anchors or by Dynamic Positioning (DP)

systems, and are referred to as such. Either type may be deployed for the

installation of BalticPipe offshore pipeline and have distinct advantages.

Dynamically Positioned (DP) vesselThe DP vessel is kept on position by constantly counteracting forces acting on the

vessel from the pipe string, waves, current and wind. The counteraction is

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provided by a computer-controlled thruster system. The DP vessel can operate

independently from other vessels (anchor handling tugs) and is therefore

potentially faster and less prone to weather downtime.

Anchor positioned vesselAlternatively the position keeping and propulsion of the laybarge may be achieved

using a number of anchors. Typically for laybarges 12-16 anchors are positioned

1000 2000 metres from the barge. For the open offshore sections this type of

vessel is generally quite large with overall lengths in the 130-200 m range.

Examples are shown in Figure 7 and Figure 8.

Figure 7 Example of dynamically positioned pipelay vessel. Allseas

Lorelay. Overall length of 182 m

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Figure 8 Anchored laybarge of the semi submersible type. European

Marine Contractors Castoro Sei. Overall length of 152 m

For pipelaying in water depths below 10 m, it may be necessary to deploy a

shallow-water laybarge. Example of such is shown in Figure 9

Figure 9 Example of shallow-water laybarge shown with pipe-handling

barges alongside

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TrenchingTrenching by pipeline plough, as shown in Figure 11, requires a mother vessel

with an A-frame for launching and retrieving the plough. This vessel also holds all

the control systems used for controlling the plough. An example of such a vessel isshown in Figure 10.

Figure 10 Typical mother vessel for large offshore pipeline plough (Far

Sovereign)

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Figure 11 Typical pipeline plough onboard the mother vessel (EMC:

pipeline plough PL2 onboard Diving Support Vessel Bar

Protector)

In hard soil conditions, additional pulling capacity for the plough may be obtained

from one or several multi-purpose vessels as shown in Figure 12.

Figure 12 Typical multi-purpose vessels capable of acting in the role as tugs,

pipe-handling vessels or as anchor handlers

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Trenching in hard soil conditions may also be performed by means of a

Mechanical trenching machine moving along above the pipeline by means of

caterpillar tracks refer to Figure 13 below. This equipment requires a support

vessel similar to that shown in Figure 10.

Figure 13 Mechanical trenching machine (Digging Donald of Allseas)

A powerful water jet, shown in operation on the left in Figure 14, are aimed at the

seabed, and brings the seabed sediment in suspension allowing the pipeline to bury

itself into the seabed. This equipment requires a support vessel or barge to operate

the pumps.

Figure 14 Example of jet sled

Fluidisation equipment is similar, but pumps are of lower pressure.

Cable retrievalCutting and retrieval of sections of abandoned cables may take place by use of a

grapnel deployed from a smaller vessel, or a larger dedicated cable vessel such as

the vessel shown in Figure 15.

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Figure 15 Example of cable installation and handling vessel

Diver Support Vessel (DSV)For diving operations a specialised diving support (DSV) vessel may be applied.

The DSV will often have the capability to function as a multipurpose vessel i.e. it

usually has cranes and a limited deck storage capacity and potentially an A-frame.

A typical example is the CSO Wellservicer shown in Figure 16.

Figure 16 Example of diving support vessel (CSO Seawell)

Welding HabitatSubsea connections may be performed as bolted flange connections or as

hyberbaric welds i.e. welds performed subsea in air inside a welding habitat

enclosing part of the pipeline both sides of the weld location. A typical welding

habitat is shown in Figure 17.

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Figure 17 Example of offshore welding habitat

The habitat is placed on top of the pipeline ends to be welded. The pipeline is

loaded into the habitat and sealed at both ends where the pipeline ends enter the

habitat seal from the outside hydrodynamic pressure. Following this the water

inside the habitat is pumped out. Following this divers/welders can manually

complete the weld in dry conditions and the habitat can be retrieved to the surface.

Rock dumpingRock dumping may typically take place using a fall pipe vessel of a side dump

vessel examples of which is shown in Figure 18 below.

Figure 18 Example of rock dumping vessels. Fall-pipe vessel on the left and

side-dumping vessel on the right

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Support vesselsOther support vessels apart from the vessels shown above may include vessels for:

Pipe transportVessel types similar to vessels shown in Figure 12 are used for hauling pipe

from the onshore storage to the laybarge.

Anchor handling vessels if an anchored laybarge is used. Vessel type

similar to vessels shown in Figure 12.

Tugs of various sizes

Construction barges

Miscellaneous small vessels

In addition to the above helicopters will be applied as the primary means of

personnel transport to and from vessels. Helicopters are preferred due to the

inherent risk of personnel transfer from ship to ship.