• Fast underwater ship hull repairs save time and money

    Fast underwater ship hull repairs save time and money

    10/06/2014

    Hydrex on-site hull repair services include the renewal of both small and large areas of damaged hull plating. These repairs can be carried out above or below water, according to the circumstances, with tailor-made mobdocks. Normal commercial activities can therefore continue without disruption. These operations follow the Hydrex procedure for welding cracks in the vessel's shell plating and they are approved by the major classification societies.

    Hydrex diver/technician teams carry out these on-site hull repairs all over the world. In most cases the damaged area can be replaced with a permanent insert and no condition of class is imposed. On the rare occasions where the damage does not allow such a repair, a temporary doubler plate is installed over the affected area. This allows the owners to keep to their schedule and have a permanent repair carried out during the next scheduled drydock visit.

    Building on an ever-expanding worldwide network of offices and support bases, Hydrex can provide these repairs at reasonable costs across the globe. All offices are fully equipped and can mobilize immediately. As part of the Hydrex Group they can take advantage of the company’s many years of experience.

    Repairs of this kind can only be done successfully by trained divers/technicians who are familiar with them and who have the relevant know-how to resolve all of the technical difficulties encountered during underwater operations. This is why all Hydrex technical staff from all offices undergo stringent training after which they are able to perform a wide range of operations. They can achieve the same high quality without unnecessary loss of time.

    To offer the fastest possible service to customers, Hydrex offices have fast response centers where an extensive range of state-of-the-art  tools and diving support equipment is available at all times for the repair teams. These fast response centers enable Hydrex to mobilize diver/technician teams immediately.

    The following case studies give an account of some of the more important hull repairs performed by Hydrex.

    Permanent underwater insert repair in Norway
    Hydrex was contacted to carry out a permanent insert repair on board a research vessel that had suffered a crack in the bow section of its hull plating. The work was carried out during the vessel’s planned stop in the port of Bergen, Norway.

    A repair procedure was devised by the Hydrex technical department and once a location had been chosen all arrangements for the needed equipment were made in close cooperation with the local support base while a Hydrex diving/technician team was mobilized to Bergen. 

    After arrival on site and installation of a workstation, both an on-board and an underwater inspection were made of the damaged area. This revealed that a 600 mm x 300 mm insert plate needed to be installed. An 800 mm x 600 mm mobdock was therefore constructed to seal off the affected area from the water during the operation.

    After the mobdock had been installed, the frame was cut out around the crack to the same size as the insert, which was then welded with a deep penetration weld according to the class-approved Hydrex procedures.

    The Hydrex team performed a permanent repair instead of installing a more common temporary doubler plate and this was all done within a very short time frame. This solution means that this area of the ship will not require further repairs during her next drydocking. The vessel could sail on time as the repair was carried out well within the stipulated time frame.

    Comprehensive bottom plating repairs in Gabon
    When a 157-meter general cargo ship scraped against the rocky bottom of the winding River Congo it suffered a dent 3 meters wide and 80 meters long on the starboard side around the bilge keel.  During this incident seven of the vessel’s tanks were pierced inside this area and filled with water. This caused the ship to list 12°. Hydrex was asked to inspect the damage and perform the external repairs needed to get the ship back in business.

    A Hydrex supervisor met the ship in Matadi only two days after the call to perform an inspection and make an assessment of the damage. Because of the poor visibility, the Hydrex technical department advised the customer to sail on to a more suitable location on the coast of Angola just south of the river mouth. As the current was going north, in-water working conditions were considerably better.

    After reviewing the results of the inspection the Hydrex technical department devised a repair plan which could be carried out at anchorage in Port Gentil, Gabon. While the vessel sailed to Port Gentil a team of four additional diver/welders was mobilized to this location.

    In total 14 cracks were sealed. The repair took only four days after which both the damaged tanks and their counterparts on port side were emptied to relift the vessel to its normal draft.

    When the Hydrex supervisor first arrived at the vessel no information about the damage was available. Thanks to the experience of the team, Hydrex was able to adapt easily to the situation and propose a solution to the customer and execute this very rapidly. 

    Comprehensive bottom plating repair on bulk carrier in Peru
    Bad weather caused a 195-meter bulk carrier to roll heavily while at anchorage in Chicama, Peru. The vessel scraped against the seabed and suffered severe damage to the forward end of its bottom plating. As the consequent intake of large amounts of water caused the ship to trim by the head, Hydrex was contacted to make a full assessment of the damage and carry out the necessary repairs.

    The vessel had just been loaded and the degree of trim was significant. Unloading the cargo while still at anchorage was not an option for the owner. Under those circumstances the vessel was also not allowed to enter any port for unloading. Hydrex was therefore asked to find a solution to perform any possible repairs on-site which would enable the ship to sail to its next stop and continue its schedule for the subsequent three months until the next planned drydocking.

    Because the bottom plating had been damaged in two different places it was decided to move the vessel to a nearby and more suitable location in Lima, Peru where two doubler plates would be installed: one on the port side to cover a crack 1500 mm long and 250 mm wide, the other to close off an opening situated on the starboard side that measured up to 3500 mm at its widest point. The proposal was accepted by the classification society and so the vessel carefully sailed to the new location at the reduced speed of 7 knots.

    While the smaller doubler plate, measuring 1200 mm x 1800 mm, was installed, a local workshop started working on the second.  Due to its size the plate was delivered in three parts and was then welded together by the Hydrex team to its full size of 6 m x 6 m. Next it was reinforced with stiffeners to make sure it would be able to withstand the water pressure. The plate was then lowered into the water, positioned over the designated section and welded underwater by certified Hydrex wet welders.

    The superintendent was very satisfied. Thanks to the on-site repair he did not have to make any time and money consuming changes to the ship’s schedule and could sail the ship until the next planned drydocking.

    On-site insert repair in Hong Kong
    When a survey done in Hong Kong revealed damage to the flat bottom shell plating of a 182- meter oil tanker, Hydrex was contacted to perform insert repairs with the use of a cofferdam.

    The inspection was performed by a member of the Hydrex worldwide network of local support bases who informed the ship owner that the damage could be permanently repaired and that Hydrex had the experience and equipment to perform such an operation.

    The repair started with the underwater installation of the mobdock on the hull. Next, part of the bulkhead and the piping that was located over the affected area were removed. Once this was done a plate measuring 550 x 550 mm was cut out of the bottom plating and the edges of the opening were ground smooth. A new insert plate was then fitted into the hole and full penetration welding was executed after which the bulkhead and piping were reinstalled.

    Thanks to the excellent communication between the Hydrex technical department and the local support base in Hong Kong several phases of the preparation for the repair were handled simultaneously and the repair work itself was performed in less than two days. This brought the total time of the operation down to the absolute minimum without any unnecessary delay for the customer.

    Extensive on-site insert repairs in Curaçao
    A Hydrex diver/technician team was mobilized to Curaçao to perform large insert repairs on a 190-meter bulker that had developed several holes in its hull.

    The repair was carried out inside a tailor-made, open-top cofferdam positioned over the damage. An expert Hydrex diver/technician flew to the location to take the exact measurements needed to design the cofferdam so that it would conform precisely with the shape of the hull. 

    When the open-top 4500x5700 mm cofferdam was installed onto the ship’s hull, all water was removed from it. This created a dry underwater area in which to work. Next the piping and framework were removed to permit access to the two affected areas and the installation of the new inserts from the outside.

    One large L-shaped insert plate was installed in two phases covering a total height of 2900 mm and a width of 4200 mm. This was followed by the fitting of a second plate with a size of 300 mm x 600 mm. Both inserts were curved in the same way as the cofferdam to fit the rounded shape of the hull.

    The operation was performed in accordance with Russian Register requirements. The diver/technician team was able to keep the time frame of the repair work to the absolute minimum of only seven days.

    Insert repair on tanker in Gabon
    Hydrex was asked to perform an insert repair combined with a presale inspection and propeller polishing on a 230-meter tanker while the vessel was at anchor in Cap Lopes Bay, Port Gentil. A diver/technician team was therefore mobilized from the local Hydrex office.

    The operation was performed with two work barges, one on which all the equipment needed for the insert repair was loaded and one on which a monitoring station was installed which was used for the underwater hull inspection. This enabled the team to split up and perform the two parts of the operation simultaneously.

    The repair operation started with the installation of scaffolding on both sides of the hull to give the team access to the affected area on the side shell plating of the vessel. Next both an onboard and an outboard inspection of the damage was performed. This revealed that an area of 2255 mm x 1760 mm needed to be cut away and replaced with a new insert plate.

    While the new insert was fabricated to the exact measurements, the affected shell plating was cut away together with several frames that were also damaged. New frames were then installed and the edges of the hole were prepared for the installation of the insert which was subsequently positioned and secured with a deep penetration weld according to the class approved Hydrex procedures.

    When the insert plate was fully welded, ultrasonic testing was carried out with positive results. The full penetration weld was also inspected from the outside, found to be in good condition and authorized by the class. This allowed the new owner to sail his vessel with a permanently repaired hull.

    Permanent underwater insert repair in Spain
    Recently Hydrex Spain carried out a permanent insert repair on a 225-meter cargo vessel at anchorage in Algeciras.  The vessel had suffered a stress-related crack on the port side next to the bilge keel and water was coming into the ballast tank. The classification society therefore required that a repair be carried out before the end of the month.

    After arrival on site and installation of a workstation, both an on-board and an underwater inspection were made of the damaged area. This revealed that a 450x335mm insert plate needed to be installed.

    Before the team could install the cofferdam that would seal off the damage, part of the bilge keel needed to be removed. When this was done and the cofferdam was in place, the diver/technicians cut away the area around the crack to the same size as the insert, which was then welded with a deep penetration weld according to the class-approved Hydrex procedures.

    During the operation similar damage was found in the same location on the starboard side of the vessel. The team therefore used the same procedure to install a 700x335mm insert plate on that side as well.

    As a result of the permanent repair carried out with the ship at anchor, further attention to the hull cracks will not be needed during her next drydocking. The vessel was ready to sail on time as the repair was carried out well within the available time frame.

    Permanent insert repair on bulk carrier in the U.S.A.
    Permanent insert repairs were performed by a Hydrex diver/technician team on board a bulk carrier that had suffered several cracks in the shell plating of its ballast tanks. In total three new insert plates were installed while the vessel was berthed in Norfolk, Virginia, U.S.A.

    A diver/technician team with equipment was mobilized from the Hydrex office in Clearwater, Florida, to Norfolk. After the designated ballast tanks were declared gas free, the team prepared and set up all the equipment for the inside work.

    They  positioned the first cofferdam on the in-water side of the hull over the first location. Next the old shell plating was removed and a new insert was installed and secured with full penetration welding. The first cofferdam was then removed and positioned over the second crack while at the same time the second cofferdam was installed over the location of the third and final cracked area. The team then removed the shell plating at both locations and positioned and secured a second and third new insert following the same procedure.

    A surveyor from the American Bureau of Shipping who was on site then tested all three inserts with ultrasonic testing equipment and approved the work.

    The repairs in this article were performed according to the Hydrex class approved procedures. Like all Hydrex operations they follow the essential professional standards to ensure the future safety of the ship.

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