CVR: 27171877 Niels Bohrs Vej 6 VestJysk Bank: 7606 1064127 DK-6700 Esbjerg, Denmark

Ministeriet for Videnskab, Teknologi og Udvikling

RAMBØLL

Access to offshore wind turbines

Screening report

DOC. NO. 4003srer1 29-03-2006

../2 info@offshorecenter.dk Tel: +45 36973670 www.offshorecenter.dk

VTU Access to Offshore Wind Turbines Screening report 2

TITLE : Screening Report

WRITER : Ulrik C. Jensen

SYNOPSIS : Screening of projects for access to offshore wind turbines

CHECKED BY : Kai B. Olsen

APPROVED BY : Kai B. Olsen

VERSION : REV. NO. DATE Remarks

1 29-03-2004 Final

DISTRIBUTION : FIRMA INITIALER

Offshore Center Danmark RAMBØLL FABRICOM Grumsens Maskinfabrik Viking Life-Saving Equipment A/S Sea Service

PB – AC KBO – UCJ GM PM CO – LB BB

CIRKULATION : FIRMA NAVN / INITIALER

Offshore Center Danmark Peter Blach/PB - file This is an unpublished work, the copyright of which vests by Offshore Center Danmark and the consortium participants. All rights reserved. The information contained herein is the property of above parties and is supplied without liability for errors or omissions. No part may be reproduced or used except as authorised by contract or other written permission.

4003sr01er1

OFFSHORE CENTER DANMARK Niels Bohrs Vej 6

DK-6700 Esbjerg, Denmark

File 359007

J.nr. 340_0001 Prepared by:. UCJ

Edition Rev. 1 Check: UCJ

Date 2004-03-29 Approved: KBO

RAMBØLL WILLEMOESGADE 2 DK-6700 ESBJERG TEL 7913 7100 FAX 7913 7280

OFFSHORE CENTER DANMARK Access to offshore wind turbines

2004-03-29

List of Contents

1. Summary and Conclusion 1

2. Access methods 3 2.1 Access method # 1 – Selstair (Viking) 3 2.2 Access method # 2 – Wind turbine crane (Grumsen) 7 2.3 Access method # 3 – Wave compensated boat (Sea Service) 7 2.4 Access method # 4 – Traditional boat landing (Rambøll) 9 2.5 Access method # 5 – Offshore Access System OAS (Fabricom) 10 2.6 Access method # 6 – Helicopter 14 2.7 Alternative access methods 14

3. Evaluation of access methods # 1 - 5 18

4. Evaluation acc. to project specifications 19

5. Conclusion 21

6. References 22 Enclosure A: Selstair (Viking) Enclosure B: Wind turbine crane (Grumsen) Enclosure C: Wave compensated boat (Sea Service) Enclosure D: Traditional boat landing (Rambøll) Enclosure E: Offshore Access System (Fabricom) Enclosure F: SWATH (Schroeder & Schramm) Enclosure G: Examples of patented methods.

J.nr.340_0001 I

1. Summary and Conclusion

The present report has been prepared according to the job specification in work packages nos. 02 and 03, project 3, “Access to offshore wind turbines” for Offshore Center Danmark (OCD). The report contains a brief description of different access methods for offshore wind turbines. In total 5 access methods are compared based on a list of advantages and disadvantages. With the comparison as point of departure, an overall assessment of the 5 access methods based on the project specifications outlined in Ref. /1/ is presented. The main items, which the projects should include as a minimum, were defined as:

1. Project description. 2. Environmental conditions. 3. Availability factor. 4. Type of foundation structure and installation tolerances. 5. Environment. 6. Total cost of project from engineering to installation. 7. Lifetime. 8. Maintenance requirements. 9. Safety. 10. Authorities.

Based on input from the project group members, commercial and financial issues have been disregarded, i.e. the report contains only technical issues and may be regarded by all interested parties as a catalogue of various approaches. According to the original scope of work in work package 03 a new and final report was aimed at being issued end March 2004 further detailing the approaches. Due to above and the fact that the involved companies would appreciate a further promotion of their access methods; they are all in a stage that further development requires financial investments and further details are being treated as confidential. Finally it has been concluded by the project group members that further interests in the respective methods should go directly to the company representatives. However, OCD is able to provide any help required. Therefore minor deviations to this report compared to the previous revision 0 are written in italic. The 5 methods (and helicopter access as no. 6) which are described in the present report should not be regarded as the only alternatives to accesses to offshore wind turbines, and examples of other alternatives are described briefly in section 2.7. Finally, a number of known patents are included in enclosure G. The methods are:

1. Selstair (Viking). 2. Wind turbine crane (Grumsen).

J.nr.340_0001 1

3. Wave compensated boat (Sea Service). 4. Traditional boat landing (Rambøll). 5. Offshore Access System (Fabricom). 6. Helicopter.

Methods 1), 2), 3) and 5) are still at a developmental stage in the respective companies but preliminary project descriptions have been included in the respective enclosures. Accounts are given of methods 4) and 6), however not at the same level of detail because the technologies are well known. Based on the screening in the present report, project evaluations, and the input from the project group members, the following methods have been selected for further evaluation:

1. Selstair (Viking). 2. Wind turbine crane (Grumsen). 3. Wave compensated boat (Sea Service). 4. Offshore Access System (Fabricom).

J.nr.340_0001 2

2. Access methods

In the following, 6 different access methods for offshore wind turbine structures are described. The methods have been elaborated on in enclosures A to E. Enclosures A, B and C contain preliminary project descriptions from the involved companies. With respect to the reservations defined in the project specifications (Ref. /1/) it is estimated that the 6 methods will cover the majority of currently known offshore wind turbine sites. The decision as to which access method is preferred will always be site specific. In turn it is impossible to point out any one access method which is most ideal in all respects, and the present report must therefore be regarded as a survey of what is currently going on within the area. Finally, section 2.7 and enclosure G presents a number of alternative methods/patents.

2.1 Access method # 1 – Selstair (Viking) Inspired by the well-known offshore evacuation chute, Viking has developed the concept of a collapsible staircase named Selstair. Selstair is lowered directly into the water, which makes access possible via a landing platform connected to the staircase. The concept has been illustrated in figure 1 and 2. A Selstair was installed at the FPSO (Floating Production Storage and Offloading) ship 15/12-B Varg in the Norwegian sector in 1997. The original concept as outlined above is considered used reversibly, i.e. the Selstair is mounted on the service vessel and erected from the deck to the turbine foundation structure. An outline proposal is show overleaf in Figures 1A to 1D. Further details about Selstair are listed in enclosure A.

J.nr.340_0001 3

Figure1: Prototype of Selstair. Source Viking

Figure 1: 3-D Sketch of Selstair. Source Viking

J.nr.340_0001 4

Figure 1A: Selstair outline proposal

Figure 1B: Selstair outline proposal

J.nr.340_0001 5

Figure 1C: Selstair outline proposal

Figure 1D: Selstair outline proposal

J.nr.340_0001 6

2.2 Access method # 2 – Wind turbine crane (Grumsen) Usually an offshore wind turbine is fitted with a crane used for the transfer of service equipment etc. Taking this as a starting point, Grumsen has suggested a ”wind turbine crane ” which lifts the MOB boat out of the water and enables the crew to climb on to the wind turbine. This access method has been described in further detail in enclosure B. The method depends on the crane being remote controlled, while simultaneously compensating for the vertical heaves before the boat is lifted out of/ and back into the water. An illustration of this method is shown in Figure 2.

Figure 2: Illustration of the wind turbine crane where the MOB boat is hoisted

out of the water with a remote controlled heave compensated crane. Source Grumsen.

2.3 Access method # 3 – Wave compensated boat (Sea Service) Based on the ”Small Water Plane Area Twin Hull” (SWATH) concept, Sea Service has suggested a wave compensated boat on the small water plane principle. Unlike SWATH, the boat is not equipped with a twin-hull, but has been designed with a thin hull at the bow. A principal sketch of the proposed wave compensated boat is shown in enclosure C together with a project description. Access takes place between the two vertical generators, and the horizontal forces

J.nr.340_0001 7

generated from the power of the vessel together with the friction in the boat landing are assumed to be able to keep the boat in position. Because of the design of the boat, Sea Service suggests that landings are established in three positions (per 120°) on the circular structure (the vessel is unstable for perpendicular wave action). Sea Service has announced that the proposal will be tested in a tank medio 1st quarter of 2004. Furthermore Sea Service announced that full-scale tests with a SWATH vessel would be carried out at Horns Rev in 2004. The vessel will be provided for the occasion by the German military and the results form these tests will be included in the further development of the wave compensated boat. Photos from the tests are shown in Figure 2A and 2B.

Figure 2A: SWAT boat at Horns Rev from test in 2004.

J.nr.340_0001 8

Figure 2B: SWAT boat at Horns Rev from test in 2004.

2.4 Access method # 4 – Traditional boat landing (Rambøll) In addition to helicopter access, offshore platforms are typically equipped with boat landing possibilities. Some unmanned platforms are however, equipped with boat landing as only access possibility. These boat landings come in all forms, but usually they are pipe-structures welded directly onto the platform. The approach from the seaside is by MOB boat, as is also the case for the wind turbine crane. A typical example of this structure is illustrated in Figure 3. In principle, approach is omni-directional for this structure. It may be directly applied to offshore windmill structures and does not call for further detailed analysis. Detailed drawings of the illustrated structure are shown in enclosure D.

J.nr.340_0001 9

Figure 3: Traditional boat landing. Source Rambøll.

2.5 Access method # 5 – Offshore Access System OAS (Fabricom) Fabricom (NL) have taken over the commercial rights from Reinout Prins on a ”telescope” access from ship to wind turbine structure. The access system has been named OAS and is essentially a pedestal crane fitted onto a vessel with a telescopic walkway. The connection to the structure is a vertical tube or similar. A plate for the landing of the OAS gangway has been welded onto the tube. The first prototype of the system was supplied to oil company Occidental and tested in November 2003 in Qatar. The following photos have most kindly been lent out by Fabricom and were taken in connection with the above-mentioned test. Fabricom has presented the system to OCD (January 2004) and a printout of the presentation is included in enclosure E.

J.nr.340_0001 10

Figure 4: OAS prototype from Qatar. Source Fabricom.

Figure 5: OAS prototype from Qatar. Source Fabricom.

J.nr.340_0001 11

Figure 6: OAS access arrangement for structure. Source Fabricom.

Figure 7: OAS access arrangement on vertical pipe on structure. Source Fabricom.

J.nr.340_0001 12

Finally, the recent development and as per project status March 2004 given by Fabricom, Figure 7A presents the OAS system now prepared for production. A further detailing of the system and possibilities is presented in Enclosure E.

Figure 7A: OAS prepared for production.

J.nr.340_0001 13

2.6 Access method # 6 – Helicopter

According to Ref. /1/ helicopter access to offshore wind turbines will not be dealt with in further detail but nevertheless it should be mentioned as an alternative to seaside access. In connection with the design of Horns Rev offshore wind turbine park Techwise (now Elsam Engineering A/S) conducted some experiments with lowering crew from helicopters onto a smaller platform installed on the nacelle. The photograph in Figure 8 shows this experiment, and Figure 9 shows the final result; a platform fitted onto each of the offshore wind mills at Horns Rev.

Figure 8: Experiment with lowering of crew from helicopter. Source Elsam.

Figure 9: Horns Rev – Access platform on nacelles for access from helicopter. Source Vestas.

It appears from Figure 9 that the access platforms are permanently installed, while other manufacturers make use of the ”add-on” principle.

2.7 Alternative access methods Apart from the methods, which have just been presented, a great number of other approaches exist. Some have been tested and yet others are still at a developmental stage. Scroeder and Schramm in Germany have devised the concept of a SWATH-boat, which has an access to the structure consisting of a gangway fitted onto the ship via a collapsible platform. A short description of the concept is enclosed in enclosure F. Enclosure G contains a number of various patented methods. Ref. /2/ is a study of cost optimising of large-scale offshore wind turbine parks. In this study a number of alternative access methods have been described that are

J.nr.340_0001 14

based on findings from Vindeby offshore park (11 450 kW wind turbines installed in 1991), where the original concept turned out to be extremely sensitive to weather. The sensitivity to weather has also turned out to be a problem at several of the more recently built offshore wind turbine parks, which is why the demands on better and safer access methods have increased. The following illustrates some of the ideas, which were presented in the study, and which might represent alternatives to the earlier described methods if they are further developed. The illustrations are self-explanatory and are taken from Ref. /2/.

Figure 10: Hydraulically managed access (supported directly on work platform)

Source Ref. /2/.

J.nr.340_0001 15

Figure 11: Hydraulically managed access (supported on main structure) Source

Ref. /2/.

Figure 12: Stair access fitted on ship. Source Ref. /2/.

J.nr.340_0001 16

Figure 13: Fender on main structure with access to platform. Source Ref. /2/.

Figure 14: Crane on supply vessel. Source Ref. /2/.

J.nr.340_0001 17

3. Evaluation of access methods # 1 - 5

Based on the 6 access methods described in Chapter 2, Table 1 presents a list of advantages and disadvantages. The following comments relate to Table 1:

• Access method # 6 Helicopter has been omitted in the comparison. • Access method # 1 Selstair has been compared based on the assumption

that the staircase is lifted of the ship onto the structure, i.e. only one Selstair per offshore wind turbine park.

• Advantages/disadvantages cannot stand-alone because the choice of access

method among other things depends on the number of wind turbines in the park. For example a traditional boat landing may turn out to be more economical than a custom-built ship if the number of wind turbines is 10. The opposite may be true for say 80 wind turbines. Financial aspects therefore have to be evaluated from project to project.

# 1 Selstair # 2 Vindturbine crane # 3 Wave compensated # 4 Traditional boat landing # 5 Offshore Access SystemAdv. No serial production Nonsensitive to marine growth No serial production Non-dependent on offshore No serial production

Nonsensitive to marine growth Flexible Flexible mechanical systems Nonsensitive to marine growthFlexible DP class vessel not required Non-dependent on offshore mechanical Simple structure Non-dependent on offshore mechanicalEasy inspection Non-dependent on tide systems Less maintenance offshore required systemsNot site specific Less offshore maintenance required May be used omnidirectional Less offshore maintenance requiredCan be used omnidirectional Not site specific DP class vessel not required Not site specificNon-dependent on tide DP class vessel not required May be used omnidirectional

100% redundant Non-dependent on tideNon-dependent on tide

Disadv. DP class vessel required Serial production Traditional boat landing required Serial production Back-up vessel requiredRemote control of crane Remote control of crane Back-up vessel required Marine growth Maintenance offshore required Maintenance offshore required Marine growth Supply vessel requiredBack-up vessel required Supply vessel required Training of personnel requiredInterface between stair and Training of personnel requiredplatform

Access Method

Table 1: Advantages/disadvantages of access methods # 1 – 5. Again, it must be emphasised that the above advantages/disadvantages have only been discussed within the project group, and cannot be treated as stand-alone. However, from the list alone the most favourable methods are seen to be systems that do not require serial production and require a minimum of offshore maintenance.

J.nr.340_0001 18

4. Evaluation acc. to project specifications

Ref. /1/ contains a set of minimum requirements which the respective project proposals/access methods must adhere to. Table 2 shows how the different proposals meet the project specifications. In addition, a weighted sum has been calculated based on the fact that the 15 criteria hold a priority from 1 to 15. The weight factor is shown in the last column where 15 has been weighted as main priority.

Project Specifications acc. to Ref. /1/ # 1 # 2 # 3 # 4 # 5 Weight1 Project description 1 1 1 0 0 112 Environmetal conditions

a) Max. wave 3.5 m 1 1 1 1 1 10b) Not dependent on wave direction 1 1 0 1 1 4c) Water depths >> 10 m 1 1 1 1 1 3d) Dependent on tide 1 1 1 0 0 2

3 Availability factor 0 0 0 0 0 94 Foundation type / installation tolerances 1 1 1 1 1 155 Environment/Cost

a) Repeatability 1 0 1 0 1 14b) Engineering cost 0 0 0 0 0 8c) Fabrication cost 0 0 0 0 0 7d) Test cost 0 0 0 0 0 1e) In-service cost 0 0 0 0 0 6

6 Lifetime/ maintenance 0 0 0 0 0 57 Safety 1 1 1 1 1 138 Authorities 1 1 1 1 1 12

Total 9 8 8 6 7Weighted total 84 70 80 57 71

Table 2: Project specifications that have been met acc. to Ref. /1/ for access

methods # 1 – 5. 1: Requirement specifications have been met (OK) 0: Requirement specifications have not been met (not OK)

With respect to Table 2 please note the following:

• The weighing has not been discussed within the project group, i.e. readers, clients or others may evaluate differently.

• Based on input from the project members, the commercial and financial

issues have been disregarded, i.e. the report contains only technical issues and may be regarded by all interested parties as a catalogue of various approaches.

J.nr.340_0001 19

• The risk assessment presented for the wind turbine crane (Grumsen) has been evaluated to be similar to the other methods, i.e. 1 has been given for safety for all methods.

From a simple addition it becomes evident that methods # 1 to # 3 take first place. If the weighted sum is used, the order is Selstair, Wave compensated boat, OAS and wind turbine crane. Not surprisingly, the latter complies very well with the advantages/disadvantages list in Chapter 3.

J.nr.340_0001 20

5. Conclusion

The present report has presented 6 different access methods to offshore wind turbine structures as well as a number of alternatives. Of the 6 methods, which have been analysed, the helicopter access has been eliminated from the final evaluation, which means that only seaside access will be evaluated. The 5 remaining methods represented by each their company:

1. Selstair (Viking). 2. The wind turbine crane (Grumsen). 3. Wave compensated boat (Sea Service). 4. Traditional boat landing (Rambøll). 5. Offshore Acces System “OAS” (Fabricom).

Of these 5 methods 4 are still at a developmental stage in the respective companies. The traditional boat landing is based on well-known technology within the offshore oil/gas industry. Of the 4 development projects, two of them include a prototype, namely Selstair and OAS. Based on the project specifications defined in Ref. /1/, the 5 methods have been evaluated. The result of the evaluation is illustrated below in priority order:

1. Selstair 2. Wave compensated boat 3. OAS 4. Wind turbine crane 5. Traditional boat landing

Part of the selection criteria is currently not described in detail in the respective project proposals, which is why further detailed information (which is regarded as essential) might change the priority order. Based on project evaluations made in January 2004 a decision was made to further detailing the number 1 – 4 methods. Due to the present status of the above mentioned approaches, and the fact that further developments are treated as confidential from the respective companies no final report has been prepared (the latter decided in agreement with OCD). However, minor corrections have been made in the present report and are written in italic. The present report concludes the work related to access to offshore wind turbines, and in that context a seminar is being arranged for 10th June at OCD. At the seminar, among other things, the presented methods and companies are planned being presented for all interested parties. Finally the present report is still meant to be a catalogue for all parties interested in offshore wind turbine production.

J.nr.340_0001 21

6. References

/1/ Memo ”Anløb til offshore vindmøller”, Rambøll Job 359007, J. nr. 320.001, revised 2003-10-03.

/2/ “Cost Optimising of Large-scale Offshore Wind Farms”, Technical Reports Vol I, JOULE R&D Programme, Contract no. JOR3-CT95-0089.

/3/ Various input from involved companies – mainly presented in Enclosures.

J.nr.340_0001 22

Enclosure A

Selstair (Viking)

J.nr.340_0001

Enclosure B

Wind turbine crane (Grumsen)

J.nr.340_0001

Enclosure C

Wave compensated boat (Sea Service)

J.nr.340_0001

Enclosure D

Traditional boat landing (Rambøll)

J.nr.340_0001

Enclosure E

Offshore Access System (Fabricom)

J.nr.340_0001

Enclosure F:

SWATH (Schroeder & Schramm)

J.nr.340_0001

Enclosure G:

Examples of patented methods

J.nr.340_0001