• Fast underwater repairs using flexible mobdocks

    Fast underwater repairs using flexible mobdocks

    28/08/2015

    Hydrex is able to perform a wide variety of operations with its flexible mobdocks. These enable us to create a dry environment underwater for our divers to work in. There is no need to send the vessel to drydock as all operations can be carried out alongside or at anchorage. Normal commercial activities can therefore continue without interruption.

    Every Hydrex office has a fast response center equipped with all the latest facilities, equipment and tools. These centers were designed specifically to increase speed of service. They allow us to mobilize our lightweight mobdocks almost immediately to operations around the world.

    This technology was first used in 2002 and has been further developed by our in-house R&D department ever since. Hydrex constantly invests in the research necessary to continue to evolve repair techniques and procedures. Over the years the Hydrex R&D department has constantly improved the flexible mobdock (mobile mini drydock) technique to make it possible for Hydrex diver/technicians to perform permanent repairs on seals, thrusters and any other part of the underwater vessel without the vessel needing to go to drydock.

    For many of these operations, we work together with OEMs. The most common type of mobdock operations are seal and thruster repairs or replacements.

    Stern tube seals
    Damaged stern tube seals will cause an increasing amount of oil leaking or water ingress as the damage worsens. By replacing the seals when the damage is first discovered Hydrex keeps the down time low. Oil leakages can also produce a potential or actual liability when for instance going to the United States or other sensitive areas. When they have a leaking stern tube, ships are often not allowed to enter ports, or they can receive very heavy fines.


    By using a flexible habitat our divers create a drydocklike environment underwater around a seal assembly. This enables our teams to perform seals replacements or other work on the housing. These repairs or replacements can be performed on a large variety of seal applications.

    It’s not always straightforward to replace seals, because there can be quite a bit of variation in the configurations of the stern tube itself. There can also be complications with the liners, which can be worn down and show ruts. All this is routinely handled by the teams on the jobs. We usually supply the equipment and the owner is free to supply his own seals. We can handle all type of seals from all original manufacturers.

    Recent case study:

    Dry shaft seal renewal underwater in Australia
    In May  a Hydrex diver/technician team carried out underwater stern tube seal repairs on a 200-meter roro vessel in Port Kembla, Australia. The ship’s stern tube was suffering an oil leak, making an on-site repair necessary.

    Taking advantage of the Hydrex flexible mobdock technique the team was able to carry out the entire repair on-site and underwater. During the operation the team removed the three damaged seals and replaced them with new ones provided by the OEM.

    Despite the remote location of the vessel, our technical department was able to arrange a rapid mobilization of a team and equipment to Australia. In the past we have carried out several operations in Australia, among which an emergency stern tube seal repair on an offshore supply vessel in cooperation with Wärtsilä.

    Bow thrusters
    With the mobdock technology Hydrex diver/technicians can carry out repair or maintenance work on all types of thrusters. A unit can be removed when it needs to be overhauled. When this is completed, it can then be reinstalled by Hydrex. With the flexible mobdock technology all water is removed from the thruster tunnel. This allows other operations to be carried out afloat as well. For example propeller blades can be replaced or repair work on the gearbox can be done on-site.


    In most cases a thruster overhaul is planned in during a scheduled drydocking. This usually means that the unit is removed in drydock. The ships then has to wait for the repaired thruster to return and be reinstalled before the vessel can leave drydock. This means costly extra off-hire time. Hydrex can however remove the unit while the ship is still afloat so it can already be brought to the manufacturer for repair. When the vessel enters drydock the overhauled unit will be ready for reinstallation without any delay. The reverse procedure is also possible. If the thruster is removed in drydock, Hydrex can reinstall it in dry conditions underwater at a later date. In this way the ship can already leave drydock while the unit is still with the manufacturer.

    Recent case study:

    Underwater bow thruster installation in stages allows vessel to stay on schedule
    Two and a half months after Hydrex diver/technicians removed the bow thruster of a 363-meter container vessel in Rotterdam, a Hydrex team once again mobilized to reinstall the overhauled unit underwater with the use of the Hydrex flexible mobdock technique. Like the removal, the operation was performed in stages at several locations to allow the vessel to keep to its sailing schedule.

    The superintendent of the ship was very happy with the first part of the operation. For this reason the customer asked Hydrex to take care of the reinstallation as well. The job was completed well within the available time frame thanks to good team work of the ship staff and the Hydrex divers.

    If you have any questions regarding a possible mobdock repair, do not hesitate to contact us.

    Animations of the procedures used can be found here (seals) and here (hrusters). For more information on mobdock or other underwater repairs, please contact one of our offices. We are at your disposal 24/7 and ready to mobilize almost immediately.

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