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 Tidewater Subsea helped redesign the cable route to improve installation success and cable lifespan. Once the proposed route was agreed upon, Tidewater Subsea completed a thorough route investigation with our observation class ROV. From the newly completed route survey, Tidewater Subsea set to building a detailed operations plan and firm pricing for the project which was accepted by the client.
 
In October 2017, Tidewater 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 Tidewater Subsea mobilized our self-propelled dynamically positioned cable lay barge (ITB 45), which is custom built to handle the wide array challenges the Pacific Northwest 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. Tidewater 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 Tidewater 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.