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Basslink subsea cable repairs rely on 18 days of clear weather

Repairing each of the three faults in the Basslink subsea cable will rely on six consecutive days of clear weather during winter in the Bass Strait.

Basslink has revealed that in order to complete repairs on its subsea cable providing energy and wholesale high-speed telecommunications services to Tasmania, it will require six days of consecutive clear weather for each of the three joints.

"As the jointing works take place on the deck of the vessel and are highly susceptible to weather conditions, each joint will require a window of relatively calm sea conditions and clear weather for six continuous days to allow such works to be completed safely," Basslink said on Friday.

"Bad weather or rough sea state can damage the cable, result in abortive jointing works, or pose unnecessary occupational, health, and safety risks for the repair crew. The jointing works are highly complex, and will see the three lengths of new cables (ie, the high voltage cable, the metallic return cable and the fibre optic cable) joined to the existing cables and bundled together, before being laid on the seabed."

The Basslink Interconnector, the world's second-longest subsea cable, has been down since December, leaving many Tasmanians without energy and internet services.

Late last month, Basslink revealed that excess water damage into its cable would result in repairs not being completed until mid-June. Prior to this, Basslink had said repairs would be done by late May.

The fault in the cable was discovered 90.5km from the Tasmanian coastline and removed and capped on Easter Sunday, three months after going down.

Basslink has now said that repair work is progressing well after the cable repair vessel was loaded up with extra resources and specialists, returning to the Bass Strait on Tuesday.

"While in Geelong, the team unloaded more than 84 tonnes of damaged cable, prepared the vessel to receive the 90-tonne cable reel, loaded additional cable and specialist equipment, and changed over some crew members," Basslink CEO Malcolm Eccles said.

"The team is currently utilising remotely operated underwater vehicles to conduct a survey of the seabed where it is proposed to lay the cable bight. We will then commence work on the first of three joints that need to be completed as part of the repair. Each joint will require six days of clear weather to complete."

Upon completion of the jointing work, the cable will be laid in the trench and on the seabed, where it will sink naturally.

Prior to telecommunications provider TPG negotiating for extra bandwidth over Telstra's fibre-optic cable to make up for its loss of services over the Basslink cable, the Tasmanian government became involved.

Tasmanian Minister for Information Technology and Innovation Michael Ferguson said in March that the state government was "very disappointed" that TPG's group of internet service providers (ISPs) had still not made provisions for the outage, "urging them to buy more capacity on the remaining Telstra cables".

"Our understanding is that customers of TPG, which includes iiNet, Internode, and Netspace brands, have been affected, while customers of other non-Telstra ISPs are provided for," Ferguson said in a statement.

"I have spoken to TPG senior management to put forward the concerns of Tasmanian customers. I have been assured that TPG are aware of the issues and will continue to expand their use of the ample Telstra capability.

"As I stated some time ago, Telstra advised there was sufficient capacity to cater for all Tasmanian retail and wholesale customers on the two fibre bundles it owns and operates across Bass Strait."

Ferguson added that he had also "reminded" Telstra Wholesale "of the importance of constructively receiving requests for more capacity from TPG".

Telstra itself commented that it is the duty of telcos to provide continued services for their customers despite outages, with Telstra offering capacity to allow this.

"Our network between Tasmania and the mainland has capacity available for our retail and wholesale customers while Basslink's undersea cable is being repaired," a Telstra spokesperson told ZDNet.

"It is the responsibility of individual internet service providers to make appropriate arrangements for events like this so their customers continue to receive the services they expect.

"Following the Basslink cut, we have been working with impacted ISPs to provide additional capacity."

Ferguson had also said that the Tasmanian government took its own services off the Basslink cable in early March in preparation for the cable cutting.

In addition to affecting TPG's Tasmanian telecommunications services, the Basslink outage also slowed down repairs to TPG's own submarine cable between Sydney and Guam, which experienced an outage in early February.