Anchor Penetration Trial in the German Bight to

Anchor Penetration Trial in the German Bight to Optimise Cable Burial Depth • ICPC Plenary – Dubai, U. A. E | 19. 03. 2014 | A. Drews, M. Petzold, D. Sinclair

The energy turn around depends on a successful grid expansion. Tenne. T is Europe´s first cross-border grid operator for electricity. With approximately 20. 000 kilometres of (Extra) High Voltage lines and 36 million end users in the Netherlands and Germany we rank among the top five grid operators in Europe. Our focus is to develop a north-west European energy market and to integrate renewable energy. Taking power further www. tennet. eu

Tenne. T‘s tasks offshore Responsible for the grid connection of offshore wind farms in the German sector of North Sea HVAC and HVDC grid connection ~ 1500 km of HVAC or HVDC subsea power cables installed, contracted or tendered (without interconnectors) ~ preplanings for another 1800 km of cables Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 3

Burial Depth Requirements in Germany for Power Cables Export Cables & Innterconnetor Offshore (from ~10 m depth contour) - 1, 5 m Do. B outside traffic separation zones - 3 m Do. B inside traffic separation zones - to avoid external threats For comparison: Waddensea: 1, 5 m Do. B Nearshore: 1, 5 – 5 m Do. B - in dependence of sediment mobility - No individual risk based assessment of burial depth for cables required - Assessment of likelyhood of damage by anchors required - Statistical approach vrs. single case Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 4

Motivation Challenges of 3 m Do. B - 3 m is no industry standard, no garantee reaching 3 m - seabed conditions – stiff clays in parts of the routes - no dredging due to environmental constraints - remidial trenching exposes cable to a higher risk of damage during installation - survey – higher measurement uncertainties - repair – longer times for recover and new reburial challenges Advantages of a reduced burial depth - meets industry standards in cable burial - larger market to deploy burial tools - time reduction in cable laying operations - time reduction for cable recover in case of a repair, easier reburial - less disturbance for ship traffic Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 5

Participants in the offshore operation 30. 04. – 03. 05. 2013 management of offshore operation anchor pull sonar and video by ROV support documentation of trials scientific support operation of sediment echo sounder scientific support operation of FS WEGA operation of side scan sonar scientific support Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 6

Chosing anchors by determination of a representative ship dwt (t) TEU Tmax (m) 50 % < 140 13500 800 7, 6 75 % < 212 37000 2600 10, 8 80 % < 231 46000 3300 11, 8 90 % < 294 80000 5700 14, 5 95 % Traffic analysis to determine a „design ship“ Cargo Ship with 80000 dwt Fractile Lenght (m) < 333 100000 71000 14, 5 -> Chose of an Hall anchor of 11. 7 t according to GL tables on correlation on anchor mass and dead-weight of ships Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 7

Anchors with chain 11, 7 t Hall Anchor & 8, 4 t AC 14 HHP ~60 m anchor chain (81 mm Gr. III) with a weight of ~2 t + 100 m steal wire ~289 cm ~280 cm ~364 cm ~ 322 cm holding capacity – Hall: 4 -6 times its mass-weight – 470 k. N to 690 k. N, AC 14: 8 -11 times ist mass-weight – 620 k. N to 950 k. N Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 8

Test Sites – Overview & Soil properties BSH Nord: loose layered fine sand water depth: 35 m BSH South: medium dense to dense sand with silt water depth: 28 m VTG: dense sand underlayed with stiff clays layers water depth: 25 m Test sites (soil densities) are representative for all Tenne. T cable routes. Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 9

Ships and their functions (1) Esvagt Connector Guardian - pulls the anchor - bollard pull of 107 t - Water pressure sensors on anchors - Multibeam - ROV with Video and Sonar - in service for Tenne. T Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 10

Ships and their functions (2) FS WEGA - Sediment Echosounder - Side Scan Sonar - operated by BSH and in service for BAW Karen M Guard Vessel for the trials in the traffic separation zone - in service for Tenne. T Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 11

Trial Program conducted (17 positions, 21 pulls) Date GMT+2 Test Start E Start N 2013 -04 -30 09: 12: 00 N 1 -AC 14 373177. 9 5998449. 3 2013 -04 -30 14: 48: 00 N 2 -Hall 373202. 5 5998349. 1 2013 -04 -30 18: 32: 00 N 3 -AC 14 373195. 0 5998253. 6 2013 -05 -01 08: 19: 00 S 1 -AC 14 374405. 1 5982347. 1 2013 -05 -01 13: 20: 00 S 2 -AC 14 374402. 6 5982247. 5 2013 -05 -01 16: 22: 00 S 3 -AC 14 374406. 4 5982153. 1 2013 -05 -02 06: 30: 00 V 1 -AC 14 369028. 0 5967145. 8 2013 -05 -02 09: 24: 00 V 3 -AC 14 369311. 5 5966932. 9 2013 -05 -02 16: 19: 00 V 5 -AC 14 369008. 7 5966646. 9 2013 -05 -02 19: 32: 00 V 2 -Hall 369203. 0 5967055. 4 2013 -05 -02 20: 55: 00 V 4 -Hall 369108. 0 5966793. 1 2013 -05 -02 22: 24: 00 V 6 -Hall 369096. 6 5966581. 4 2013 -05 -03 08: 45: 00 S 4 -Hall 374395. 1 5982049. 0 2013 -05 -03 09: 48: 00 S 5 -Hall 374392. 6 5981953. 2 2013 -05 -03 10: 54: 00 S 6 -Hall 374394. 8 5981848. 7 2013 -05 -03 13: 12: 00 N 5 -Hall 373196. 8 5998049. 8 2013 -05 -03 14: 23: 00 N 6 -Hall 373199. 3 5997951. 8 Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 12 Coordinates from GPS Log Esvagt Connector

Trial program – Pre-Survey Seabed properties on trial areas are known by surveys covering the test side or data from wind farms close by Offshore Pre-Survey: - Side Scan Sonar and Sediment Echosounder on every test site to - assess soil conditions - detect obstacles - determine position for anchor drop Example here: VTG test side Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 13

Execution of Trials close to real anchoring - Anchor was lowered to ~10 m above seabed and dropped also no free fall in a real case – chain, leads and water column give resistance to a free fall – (pre-calculations to assess the deviation from reality) - Investigation of anchor position and chain by sonar and video worst case -> highest penetration depth can be reached with a straight anchor chain and a well positioned anchor horizontal on the seabed alignment of anchor and chain by ship movement in a real case anchor droppes into a random position on the seabed - Start of pull by forward move of the ship „Esvagt Connector“ - pull until breakout of anchor - pulling forces limited to 80 t to recover the anchor Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 14

Trial Program – Post Pull Survey Side Scan Sonar, Multibeam, and Sediment Echo Sounder survey of anchor tracks Video on final position of anchor chain Multibeam Record Example: VTG Position 3 | AC 14 AC-14 V 3 Pull Distance in Force in UTM East UTM North Meter Metric Tons 369312 5966934 369310 5966929 369330 5966929 20, 00 max 78 Soll Position Anchor Penetration Trial | ICPC Plenary Drop Position Final Position 19. 03. 2014 15

Side Scan Sonar - VTG Position 3 | AC 14 - SSS used to plan SES lines final position m drop position m Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 16

Sediment Echo Sounder - VTG Pos. 3 | AC 14 SSS Max. penetration depth measured by SES: 0. 19 m Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 17

Video - VTG Position 3 | AC 14 - anchor fully covered with a clay load on base after pull Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 18

Penetration Depth recorded - pulling force complies and exceeds the holding power of the anchors –> therefore, results are realistic and comparable to a real anchor event! Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 19

Trial Results Measured Results - anchor penetration depth is less 1 m for both anchor types (including all measurement errors) - anchor resists on seabed after drop Additional calculations and interpretations - addition of geometry error gives a theoretical maximum penetration depth of 1, 2 m - the fluke tip to shank distance may be used as an estimate for the penetration depth (1. 0 m and 1. 2 m for AC 14 and Hall respectively) - extrapolation to a 29 t anchor gives a theoretical penetration depth of 1, 6 m Do. B of 1, 5 m is agreed with the German authorities also for the TSS Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 20

Public Availablity of Results Reports and Videos will be made public available on the SCUK web page or send me an email with your request: anja. drews@tennet. eu Anchor Penetration Trial | ICPC Plenary 19. 03. 2014 21