Work to lay 25km (15.5 miles) of cable off Cornwall for a £42m wave energy scheme has been halted.
The process, delayed three times last week because of equipment failure and weather, finally started on Saturday.
However, problems recurred with a flotation device, and part of the cable sank while being floated to land from a ship 2km (1.25 miles) offshore.
The work has now been put on hold until at least Tuesday while divers attach new buoyancy units to the sunken cable.
Once this is done and the cable is refloated, when its end is about 200m (650ft) off Hayle Towans Beach in St Ives Bay, it will be winched up the beach at high tide and joined to a nearby electricity substation.
Then, when the tide retreats, the buoyancy aids from the cable will be removed and tests carried out.
Afterwards, the ship Nordica will sail out about 14km (9 miles), to what will be the wave hub's final location about 16km (10 miles) offshore, laying the cable directly on to the sea bed.
The cable is longer than the required 16km because it is to be buried under the sea bed.
Once that has happened, the 12-tonne hub, which is also on board the Nordica, will be lowered on to the sea bed.
The hub, which will send energy from machines on the sea surface to wave power units ashore which link to the National Grid, is due to undergo a series of tests in the autumn.