Hydrex Mobdock Shapes Up for Tricky Hulls

Last month saw a flurry of activity for Hydrex dive teams, with a number of hull repair and shell plate projects in Europe and the United States.

All repair projects were carried out while the vessels remained afloat and on hire using the Antwerp-based company’s award-winning mobile drydock technique, mobdock. However, the repair to the flat bottom plates of vessels in the Port of Santander and Palm Beach required a more bespoke solution.

A 115m LPGC had just left drydock in the Port of Santander, Spain, when damage to the flat bottom was discovered, but since returning to drydock was not an option due to unavailability and cost, Hydrex was contacted to carry out the repair. The vessel’s shape, however, necessitated the design of a bespoke mobdock (mobile drydock) so technicians could carry out the repair underwater in dry dock-like conditions while the ship was berthed alongside the repair yard.

Once diver/technicians discovered the extent of the damage, which required a 400x300m insert, they began to tailor-make a mobdock on site to fit the rounded shape of the hull.

The mobdock was constructed at the yard for installation by the Hydrex team. The shipyard team was then able to effect repair in the best possible conditions, keeping the vessel on-hire and on schedule without having to wait for a drydock space to become available.

A tailored mobdock also had to be constructed in Palm Beach, USA, to facilitate the repair of a section of hull affected by corrosion. The damaged area was the aft starboard side shell plating by way of the bilge so it was imperative that the mobdock could sit perfectly over the rounded shape of the hull.

After the modified mobdock was installed, the frame covering the damage was removed. This allowed the diver/technician team from the Hydrex facility in Tampa, Florida, to cut away the damage and the surrounding area. A new insert plate was then positioned and welded following our class-approved procedure.

“This is the real beauty of the mobdock concept,” says Dave Bleyenberg, Hydrex Production Executive. “We can modify or build custom-made solutions on site to suit any shaped hull or appendage in very little time. This way most repair projects can be carried out underwater, in dry condition.

“Of course, there are occasions where damage does not allow a permanent repair, but we can install temporary doubler plate over the damaged areas, allowing vessels to keep sailing until their next scheduled drydock. This was the solution offered to the operator of an offshore supply vessel recently, when a small hole was discovered in the hull on the starboard side of the flat bottom. A minor patch repair like this can easily be carried out in less than a day without any interference to a ship’s schedule.”

A hull repair to a 198m general cargo ship berthed close to the Hydrex facility in Antwerp was, however, a lot less straightforward.

A detailed inspection of the vessel revealed corrosion damage in the flat bottom but shell plating around the damage was in poor condition and too thin to accommodate the welding of an insert plate. Instead, four large doubler plates were inserted on the inside of the hull to cover the damage and other areas at risk.

“The 1255 x 400 mm plates were cut to size at Hydrex HQ’s fast response centre and then fitted and secured by our diver/technicians. To prevent any further leaks, additional welding work was carried out to the rest of the area before detailed thickness measurements were taken to make sure the vessel could sail safely until the next drydock visit,” said Bleyenberg.