Ampelmann, making offshore access as easy as crossing the street Safety considerations for marine personnel transfer

J. van der Tempel Delft University of Technology

The Ampelmann Company j.vandertempel@tudelft.nl + 31-15-278 6828

www.ampelmann.nl

Abstract The main problem in the transfer of personnel and equipment from a moving vessel to a fixed offshore structure is the relative motion between vessel and structure. To overcome this problem, this paper explores a new transfer method: the Ampelmann. This system consists of a vessel mounted Stewart platform. By measuring the vessel motions and real-time control of the actuators in the platform, the top deck becomes stationary compared to the fixed world, taking away all relative motions. The Ampelmann system can be installed on any PSV or anchor handler. Typical installation time is 8-12 hours. The unit is welded to the deck of the vessel and does not require additional deck stiffening. It comes with its own power supply and motion sensor system and is therefore fully independent of the vessel’s systems. The Ampelmann gangway can be used on any fixed offshore structure without preparations. The rubber tip is pressed against a walkway, balcony or ladder and the gangway control then switches to “free-floating” mode in which the gangway can telescope, slew and luff passively, following any residual motions or slow drift motions of the vessel. The advantage of full motion compensation is that the operations are always the same for both operator and the crew transferring: in high or low waves conditions the unit is always stationary. The current design has a cylinder stroke of 2m. This allows full compensation on a 50m vessel up to Hs = 2.5m and Hs = 3.0m on a 75m vessel. Maximum operating conditions to date were Hs = 2.8m and wind speed of 7 Bft. Other criteria become limiting under these circumstances than the transfer itself: walking the deck of the ship with green water on deck or wave spray hitting the spider deck. For this concept a full scale Demonstrator was developed in 2007. The unit has performed a first commercial project in the summer of 2008 and will be deployed on several other projects. 750 transfers have been performed in 170 landings visiting 8 different structures. This paper describes the development of the technology and the safety considerations that have been the driving force in all design steps. Furthermore, the test results and developments to the future are described.

The Ampelmann concept The Ampelmann idea was born in Berlin in the summer of 2002. During a conference on offshore wind turbines, the inventors sat in on a presentation on access to turbines. Later, doing a tour of the city and having a beer, they discussed the issue. They soon came to the core of the problem of any offshore operation: the ship moves and the structure is stationary. The solution was as simple as it is effective: why not use the motion base of a flight simulator on a ship, to compensate all these motions? With the general concept in mind, all the invention needed was a name: Ampelmann after the little man in the pedestrian traffic lights in Berlin: das Ampelmännchen, figure 1.

Figure 1 Der Ampelmann, name giver and mascot to the concept

Upon returning from Berlin, several experts were consulted on ship motions, flight simulators and measurement systems. Several design studies were carried out to test the feasibility on paper. And with no extraordinary results emanating from these studies, a scale model test was set up at the end of 2004.

Dry Testing During the Dry Testing, the small Stewart platform was mounted on top of a larger Stewart platform as shown in figure 2. This larger platform is called the Simonita and is located at the faculty of Mechanical Engineering of the Delft University of Technology. Simonita can simulate the motions of a ship's deck in any sea state, which then has to be compensated by the upper platform. This method allows the Ampelmann system to be tested in various frequency ranges, and makes fine-tuning of the control system possible. The major advantage in this test phase is the fact that the simulated motions are completely controllable and therefore allow thorough testing in a safe fashion.

Wet Testing For the Wet Testing, the small Stewart platform was fixed on a scale model vessel, figure 3. The vessel was subjected to waves in the large wave basin of the faculty of Civil Engineering at the Delft University of Technology. This basin can create both regular and irregular waves at different frequencies and with different amplitudes, which makes it the ideal testing facility. Again, the system was tested in various frequency ranges, and further fine-tuning of the control system was done. Moreover, the wet tests proved the system's seaworthiness. Demonstrator Upon successful completion of the scale model test, a plan was drafted to prove the concept in real offshore conditions. Backed by government subsidies and university and industry sponsoring (Shell, SMIT a.o.), a full scale unit was designed, built and tested. The system design started in September 2006 and components were ordered in January 2007. In May, the main components were finished and delivered to Heerema Zwijndrecht where the Ampelmann team were granted work space to construct the unit. Figure 4 shows some steps in the assembly process.

Figure 4 Assembly of Ampelmann, May 2007

When the platform was assembled, the control software was tested. First one cylinder at a time was actuated, then all six and the motion envelope was tested to see if all components could follow all positions of the platform. These tests are shown in figure 5.

Figure 5 Controlling single cylinders and motion envelope testing

Figure 2 Dry Testing set-up Figure 3 Wet Testing set-up

After completion of the platform assembly and control system programming, the Ampelmann was loaded on a barge for the first two offshore tests end of June and early July. Wave conditions were Hs = 1m on the first test and Hs = 1.5m on the second test. Residual motions measured on the transfer deck were less than 4 cm heave and less than 0.5o roll and pitch. Figure 6 shows some shots of the motion compensation tests outside the Port of Rotterdam.

Figure 6 Motion compensation tests off the Port of Rotterdam, June & July 2007

A successful transfer was executed on Friday, December 14th 2007 at the offshore wind farm off the Dutch coast. Figure 7 shows the images of the transfer.

Figure 7 Transfer to WTG 03 on December 14th 2007 Safety considerations in design The goal of the Ampelmann is to make offshore access as easy as crossing the street. Catchy as the phrase may be, it creates a real challenge to the development. When crossing the street, people need to be aware of the environment they are in and make a sound judgment before stepping onto the road. The same goes for people crossing the Ampelmann, provided that the Ampelmann is performing its task correctly: providing a motionless transfer deck. But, contrary to crossing streets, the Ampelmann is a continuously operating system, measuring and actuating to compensate the wave motions. This means that the system itself needs to be designed is such a way that it will continue operating, even when components fail, to make the transferring crew focus only on their crossing. Component design for safety The design of the Ampelmann started with doing a thorough study of different fields also focusing on continuous safe operation: airplane auto pilots and automatic landing, drive by wire in cars and medical equipment. At the Delft University flight simulator Simona, a Failure Mode Effect Analysis meeting was held with experts on hydraulics, controls, offshore and flight simulators. This FMEA helped draft the first contours of safe operation. The system needs to meet the following specifications:

• Operation must continue even with single component failure • This ride-through-failure must work for at least 10s

This design approach led to the following components being doubled up in the design:

Table 1 Redundant components following FMEA studies

Required Redundant Power 200 kW 2 x 200kW + PTA valves 6 12 electrical 230 V Ship + 6 UPS Control 1 computer 4 systems

To connect component failure occurring to the operational procedures, several HAZID meetings were held with all stakeholders in the development of the Ampelmann Demonstrator. The outcome of these meetings lead to the drafting of the ASMS: the Ampelmann Safety Management System. In this extensive spreadsheet based model, all possible failures are connected to a warning level. Table 2 shows the 4 states: green for all normal, yellow for minor warnings, such as clogged filters, orange for mayor single components failing, but being backed up by the redundant unit, code red for system failure: double failures.

Table 2 ASMS failure mode codes and actions The colour codes are only visible to the operator. He has the overview to assess whether the man transferring can abort or finish his operation before he returns the system to settled position. Only code red is relayed to all of the crew: alarm lights will flash and sirens will sound. The person transferring has 5 seconds before the system will retract itself from the structure. He can either complete the transfer or step back and hold on tight. During the 5 seconds, the operator also has the option to abort the operation manually. The layout of the control panel and the alarm tree are shown in figure 8.

Figure 8 Alarm tree on transfer deck and control panel with platform

and gangway controls and failure mode status lights Transfer and connection of gangway To allow safe access, the gangway is extended towards the structure and as soon as it touches, it is switch to “Free-Floating”. In this mode, the telescoping cylinder is under constant pressure outward. This means the tip introduces a force of 500kg on the structure. Should the vessel slowly drift away, the gangway will automatically extend under this pressure. When the vessel moves towards the structure, pressure relief valves will bleed the excess oil, retracting the gangway, but maintaining the tip touching the structure, so no gap appears. In the slewing and luffing direction, the hydraulic overflow works in similar fashion. With the gangway in free floating, all residual motions are compensated passively. The freedom of movement is such that the Ampelmann compensation can even be turned of, with the passive system still following. Figure 9 shows the gangway in its extreme positions.

Figure 9 Ampelmann and gangway design and operational limits

Code Status Action All OK GO Alert GO Non critical failure Finish operation Critical failure Finish or hold on: 5 sec.

During the transfer procedure, the initial plan was to have the crew waiting in a special safe waiting area where they could strap themselves into safety belts. The precaution was taken for any failure of the Ampelmann motion compensation system to introduce large acceleration into the transfer deck. Operational experience proved that is far more effective to have the crew at the end of the gangway, ready to make the step when the tip presses against the structure and not having to cross 12m to the structure. This new procedure significantly reduces time: only 10s of contact is required. Furthermore, the entire docking procedure becomes a hit and run operation:

• Operator and crew enter platform • Bring platform to neutral position • Rotate transfer deck until gangway pointing at structure • Gangway telescoping to 2-3m extended • Master moves vessel toward structure • When desired distance is reached (app. 8-9m) gangway is extended further (1-2m) and pressed against

structure • Transferring crew to asses connection • When OK � transfer • Sail away and retract gangway

After 15 practice runs, this procedure could be completed in 1-2 minutes. The connection time, before the pressure on the tip of the gangway pushes the vessel away is approximately 30s. Enough to make successful and safe transfers. With the system commissioned and tested, it went on its first commercial job in May 2008. P14-A removal SMIT Marine Projects was awarded the contract for the removal of Wintershall’s P14-A platform of the Dutch coast. The Dutch HSE (SodM) required SMIT to use a more sophisticated transfer method than a passive gangway. As sponsor of the Ampelmann Demonstrator a year earlier, SMIT decided to use the Ampelmann for this job. As SodM had been involved in the development of the unit, it was aware of its capabilities and after a final onshore demonstration, the use of the system was approved. On May 19th, the system was mobilized to SMIT’s quayside for installation on the Taklift 4 on Thursday, May 22nd. The previous day, the T frame was already welded onto the deck and the installation comprised of bolting the Ampelmann to the frame, installing the power packs and control container and connecting the hydraulics and control wiring. Within 1 day the system was operational and load tested. Figure 10 shows the lifting of the unit by the sheer leg barge Apollo and the load testing on the Taklift 4.

Figure 10 Lifting of the Ampelmann by the Apollo and load testing on the Taklift 4

Figure 11 Ampelmann configuration on board of Taklift 4, providing access to P14-A

The next day, the spread set sail for the P14-A platform 20 miles off the coast of The Hague where it arrived late that afternoon. After setting the 4 point anchors, the first team was transferred to the platform. The most convenient place for the first landing was a balcony at LAT + 12m as shown in figure 12.

Figure 12 First landing on balcony and landing zone on spider deck.

To facilitate the transfer of the 18 men work force, a landing zone was installed on the spider deck. The landing zone provides an easy target for the operator and a horizontal sliding plate and vertical bar to press the tip of the gangway against during transfer. The hydraulics of the gangway are switch to “free floating” when on the landing zone: the telescope cylinder is pressed outward, giving a contact force of 500 kg horizontally to follow any residual motions. The luffing cylinders are pushing the gangway downwards with 50 kg vertical force. Should residual motions require the gangway to move in the other direction, passive pressure relief valves allow the gangway to follow. The slewing motion is followed passively by opening the slew valves in the free floating mode. For the preparation of the topside lift, the crew of 18 were transferred in the morning, shuttled for lunch and retrieved in the evening. The system had its first full test during the first days. Wind and waves increased to a 7 Bft summer storm with significant wave heights up to 2.5 – 3m. As the visual estimation of the wave height proved to be impractical for system operation, the vessel motion measurements and compensation simulation of the Ampelmann system was used: when motions were within the Ampelmann envelop for a period of 15 minutes prior to intended transfer, the operation could start. Eventually, the system was unable to operate for only 3 hours, where the conventional gangway would not have been able to work for a full 5 days. On June 5th, the topside was lifted off and sailed to the Port of Rotterdam, as shown in figure 13.

Figure 13 Lifting of the P14-A topside and sailing back to port

The jacket was removed in the following weeks as shown in figure 14.

Figure 14 Preparing the jacket for removal

Lessons learned The Ampelmann system adds significant value to a decommissioning spread for small platforms. The preparation works typically take 2-3 weeks and are no longer limited by weather where access is concerned. The operational procedures were tested in practice and updated where required to make them more intuitive. The total turnaround time for transferring 18 persons was 15 minutes. Most of this time was taken up by retracting and rotating the gangway. To increase the efficiency, the operation speeds of the gangway system will be increased in the near future. A total of 750 transfers were performed in up to Hs = 2.8m and Bft 7 wind speeds. To decide whether the system can still operate when environmental conditions deteriorate, in this project the visual estimate of the significant wave height was used. During the project it was decided to use the Ampelmann measurement system readouts in stead: they give a more accurate image of the ship motions and of the Ampelmann performance, rather than a visual interpretation of the waves. It was clear that in some sea states the wave height was estimated higher, even though the vessel motions were still within Ampelmann compensation boundaries. The Ampelmann readout will be made available on the bridge of the vessel next time to serve as objective decision tool. It could also be extended to cover crane workability limits. DP-class PSV The Ampelmann has been tested further in the North Sea in September 2008 and January 2009 on different vessels. In September, the unit was mounted on the 50m long DP-I Esvagt Connector for a trip visiting several Danish platforms. The unit was installed 3m above the deck to avoid major removal works on the vessel. The higher location allowed the gangway to connect to balconies higher up on the offshore structures. The location was less favourable for motion compensation, as roll motion translates to horizontal displacements larger than the Ampelmann envelope for larger wave conditions. For future deployment, the unit needs to be installed at deck level. During the test 3 platforms and 1 buoy were visited and several landings were performed. An extensive measurement campaign proved the correct working of the system. The DP system of the vessel is somewhat influenced by the free-floating pressure of the gangway. During the tests, the Ampelmann operator and DP operator did manage to include the influence in the DP control, preventing further interaction. After this, the DP was stable. Figure 15 shows the Ampelmann on board the Esvagt Connector and landing on a monopile platform.

Figure 15 Ampelmann on Esvagt Connector, a 50m long DP-1 vessel, and landing on a monopile In January 2009, the Ampelmann was installed on board the Base Express. The vessel arrived on Monday at 9:00 AM, the deck was prepared, the Ampelmann installed and tested and the vessel set sail on Tuesday 18:00. A test was performed upon arrival the next day from 9:00-17:00. On Thursday the Ampelmann system was on the quay side again. A round trip including mob and de-mob in 4 days. The system was tested on the L7 platform on the Dutch Continental Shelf. Several vessel headings were tried: head, beam and stern waves. During the tests, DP failure modes were tested and proved the operation could continue without problem. Figure 16 shows the Ampelmann during installation and testing on the Base Express in the Port of Rotterdam and landing on several angles at the L7 platform.

Figure 16 Ampelmann installed and tested on the Base Express and operating under different headings at the L7 platform

Conclusions and outlook The Ampelmann system was developed and tested thoroughly on different vessels and structures. The concept proves to offer safe and easy access to offshore structures, without the need for significant landing stations or other adaptations to the structures. The unit is “plug & play”, installable on any vessel with sufficient deck space in under 2 days. An overview of workability on different vessel sizes is shown in figure 17.

Figure 17 Candidate vessel for mounting an Ampelmann and their workability Currently a new Ampelmann system is under construction. It will start operation on a job in the UK early June 2009. The new system has been improved on details with lessons learned from the Demonstrator. The main changes are the length of the gangway being extended to maximum 20m and the hydraulic hoses being placed on the inside. Ampelmann is set on making their motto an industry standard:

Offshore access, as easy as crossing the street.

Type vessel: Anchor handling tug Dimensions: 24m x 10m x 2.75m Displacement: 120 tons Max. sea state: Hs = 2.0m Workability: 85% (Southern North Sea)

Type vessel: Multi purpose vessel Dimensions: 50m x 12m x 3.80m Displacement: 900 tons Max. sea state: Hs = 2.5m Workability: 93% (Southern North Sea)

Type vessel: Offshore support vessel Dimensions: 70m x 16m x 5.60m Displacement: 4000 tons Max. sea state: Hs = 3.0m Workability: 97% (Southern North Sea)