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Sechelt Narrows Cable Project - October 2017

The Bluearth Renewables Sechelt Narrows project is a 138kV cable crossing just south of the famed Skookumchuck Narrows which has daily currents reaching 14 knots.  For this project ITB Subsea helped redesign the cable route to improve installation success and cable lifespan. Once the proposed route was agreed upon, ITB Subsea completed a thorough route investigation with our observation class ROV. From the newly completed route survey, ITB set to building a detailed operations plan and firm pricing for the project which was accepted by the client. 


In October 2017, ITB Subsea mobilized its dive team to the project area to assist Dent Construction in building the shore landings, the civil works were estimated at 18 days and were completed in 14 days. Civil works consisted drilling and setting sleepers for the HDPE conduit, installing 5 HDPE conduits on steep uneven bedrock, drilling and setting rock anchors for cable anchors, forming and pouring concrete pads for cable anchors and assisting in backfilling the cable shore landings with rock armor.


With the civil works complete ITB Subsea mobilized our self-propelled dynamically positioned cable lay barge (ITB 45), which is custom built to handle the wide array challenges the Pacific North West regions offers for submarine cable projects. Due to the high currents in the project area, the project could only feasibly be conducted safely within an 8-day period every 6 months during daylight hours. ITB Subsea successfully completed the project in 4 days on site with zero overtime and only 3 hours of downtime which ultimately was made up and did not impact our overall schedule.


The cable was laid using our brand new 500 mt turntable and 15mt state of the art linear cable machine, these machines operating off our DP cable barge with the use of our custom in-house cable lay software which is specifically designed for the rugged bathometry of the PNW, allowed ITB Subsea to lay the cables in very accurate positions and finely controlled residual bottom tensions. Accurate positioning and finely controlled residual bottom tensions are integral to providing a cable lay with minimal cable spanning, proper cable bottom embedment and cable strumming control, which is the vibrating of cable when in span that acts like a sawing motion on the cable at its touchdown points and fatigues the cable in span. While spans are not always avoidable due to bathymetry and cable stiffness, pre-calculated vortex induced vibrations at set residual bottom tensions can find the optimal residual tension to lay the cable at, reducing the strumming action and increasing the cable lifespan.


Through proper planning and execution, ITB Subsea completed the Bluearth Renewables Sechelt Narrows project on time, within budget and did not require additional post lay armoring or span remediation operations which are generally costly and hard to budget for.

Industra Pipelay - 2017
  • Dive: Build and Install Fresh Water Pipe

  • Project Duration: Three Weeks

  • Dive crew set up on shore and fused two 500 meter pipes from the beach

  • Pipes weighted with concrete saddle weights and floated into a storage area until directional drilling complete

  • Pipes towed by ITB cable skiffs into final position

  • Divers monitored sinking, make initial connection while cable skiff controlled positioning and sinking rate

  • Divers connected offshore intake screen and performed as-built survey

BC Hydro: Pender Island Repair - 2017
  • 2 identical anchor strikes on the same cable system within 3 months of each other and separated by 5 meters

  • Project Duration: 1 Week each

  • Divers and ROV mobilize ahead of cable vessel to survey and prepare shore ends of cable

  • ITB loads cable onto the Georgia Transporter in Vancouver

  • GT Sails to project site and begins damaged cable recovery

  • Performs 3 splices on location to repair the circuit

  • Demobilized back to Vancouver and offloads damaged cable for evidence in ensuing court proceedings against deep sea vessel operators

BC Hydro: Bowen Island - 2017
  • Project Duration: 2 Weeks

  • Project utilized ITB 45, both ROV’s, Divers and external tugs

  • Survey cable right of way

  • Assist Hydro in shore landing construction

  • Recover old cables

  • Install new 3 core 25kV cables

Big Silver Cable Laying Project - 2015

The Westpark Electric Harrison Lake cable project is a 138kV cable crossing in a remote lake within British Columbia. This cable crossing provided additional obstacles to standard cable laying as the lake was inaccessible to our ocean-going fleet, 240-meter depths in the crossing and steep underwater cliffs on both sides of the lake. For this project, ITB Subsea demobilized the ITB 45 at our Vancouver marine facility and built a custom, dynamically positioned lay barge from the 45’s components and flexi-floats in a remote disused log sort on the lake.


Mobilizing this self-propelled barge amounted to building a small ship out of modular components over a 5-week span in the BC wilderness. Prior to mobilizing the self-propelled cable lay barge, ITB Subsea mobilized their observation class ROV and performed detailed surveys along multiple proposed routes up and down the cliffs on both shore landings. A final route was laid out by ITB Subsea and accepted by the client within the right of way.


With the route approved, final cable design was completed by ZTT cables and, using ITB Subsea custom cable engineering software, detailed cable lay calculations were completed. Once mobilized in the lake and with shore landings complete, ITB Subsea laid 3 main cables and 3 emergency spare cable lengths in a designated wet storage area over a 7-day period. Each cable was precisely laid to reducing spanning, minimize sharp bends in the cable as it went over cliff edges and embedded the cable along ledges of the cliff where possible. Extreme diligence was given to each cable at the bottom of the cliffs to avoid excessive spanning while positioning the cables in an area that provided the maximum protection from sloughing material off the walls of the underwater cliffs. Without the detailed and thorough planning of ITB Subsea coupled with the ability to think outside the box, these projects could not have been completed in a professional manner within their budgeted timelines and cost.

Big Silver Cable Laying 2015
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