An 86-meter offshore supply vessel needed the stainless steel belt in one of its thruster tunnels replaced. A Hydrex diver/technician team therefore flew to Pointe- Noire, Congo to perform the repairs.
The stainless steel belt is installed around the perimeter of a thruster tunnel at the location of the thruster blades. There the impact of the cavitation caused by the movement of the blades is the most severe. Extra protection against cavitation damage is therefore essential. When the stainless steel belt in the thruster tunnel of the research vessel suffered cracks, the underlying steel was exposed to cavitation. The belt needed to be replaced as soon as possible to prevent the thruster tunnel from getting damaged too severely. The owner of the vessel would have had to take his vessel to drydock if no on-site solution was found.
Repair and maintenance to thrusters without the need for drydock saves time and money. Hydrex provides a worldwide fast-response solution to deal with most thruster problems, including complete overhaul and replacement of blades or seals of all types. The work is done on-site and underwater and can usually be completed within a few days of contact.
Underwater solution proposed by Hydrex
A tailor-made open-top cofferdam was designed by the Hydrex technical department. It was constructed in a local workshop in Pointe-Noire under the supervision of Hydrex diver/technicians. At the same time a regular shaped second cofferdam was also built. Cofferdams like these are used to close off the thruster tunnel on both sides. Water can then be drained from the tunnel, creating a dry working place. This allows the team members to descend into the tunnel through the open top. They can then carry out any necessary welding work in drydock-like conditions.
This prevented an unscheduled drydock visit for the ship and saved the owner precious time and money.
After the cofferdams had been constructed they were transported to the vessel’s location in Congo. The diver/technician team then started the underwater operation. However, infrastructure and dredging work in the port of Pointe-Noire brought the visibility down to almost zero. The safety of the divers could not be guaranteed. For this reason Hydrex proposed a new location for the operation.
Moving the ship to a sheltered location close by
The owner gladly accepted the proposal to move the research vessel to Port Gentil, Gabon. Port Gentil offers safe anchorage for all types of vessels (up to ULCC) on a sand/mud seabed with depths up to 50 meters and more. Thanks to the sheltered environment of the bay the swell is limited. This makes it an excellent location to carry out repair or maintenance work on a ship, barge or rig and this in ideal conditions. The central location on the African West coast also makes Port Gentil the ideal place for a Hydrex logistic and equipment support base for the entire region. This allows us to mobilize to any other suitable location in West Africa in a very short time frame, making both emergency and scheduled operations possible.
After a short trip the ship arrived in Port Gentil with the Hydrex team and all the equipment on board. A diving station was set up and the diver/technicians started the installation of the cofferdams. Next they emptied all water from the thruster tunnel. They then descended into the tunnel and carried out the repair. The old, damaged, belt was removed and replaced with a new stainless steel belt.
The actual operation was finished in only five days. The team removed the cofferdams and the ship was ready to continue its schedule with its thruster tunnel fully protected against cavitation once more.