What knot to do

Contact Energy recently purchased a new underwater ROV (remote operated vehicle) to complement their gate inspections.

A test drive was undertaken at Clyde Dam to train operators in its use before deploying the ROV to a more risky deep dive to the sluice gates at Roxburgh Dam. However the operators accidentally managed to tie the umbilical cord in a knot at 20m depth around a beam in front of unused intake No.6. This was confirmed by the ROV video! Unable to untie the knot divers were required the following week to safely salvage the ROV.  

ROV, The knot, and The ROV safely retrieved by diver and crane.