In Venice the problem of floods has become ever more frequent and intense in the last decays. The Mose system is being constructed to safeguard Venice and the entire lagoon area (550 km2) from high waters. It consists of barriers made up of mobile gates able to temporarily separate the lagoon from the sea and protect Venice from both exceptional destructive events and more frequent high tides, even if the sea level rises significantly.
Mose, is heart of a major systemic program of measures combining physical defence with restoration of the morphological equilibrium of the entire lagoon ecosystem. This multidisciplinar plan of interventions is constructed by the Ministero delle Infrastrutture e dei Trasporti - Magistrato alle Acque di Venezia through the concessionary Consorzio Venezia Nuova, that it is made up of major Italian construction companies and local cooperatives and firms.
Grandi Lavori Fincosit, as one of the major Companies that composed Consorzio Venezia Nuova, is one of the Companies involved in the construction of the Mose system.
Mose consists of a series of barriers made up of mobile gates located in the inlets (the three openings through which the tide enter in the lagoon). When inactive, the gates are full of water and completely invisible, resting in housing structures in the seabed. When there is a risk of particularly high tides which could cause flooding, compressed air is pumped into the gates, emptying them of water. As the water is expelled, the gates rotate around the axis of the hinges and rise up until they emerge and block the tidal flow entering the lagoon. The gates remain in operation for the duration of the high water only. When the tide drops and the water levels in the lagoon and the sea are the same, they are filled with water again and return to their housing structures.
“In case of the MOSE project, the doors are hinged by means of “aeration”: the doors are kept in a horizontal position on the seabed as a result of ballast (water); by pumping out the ballast, they will “float” and obtain a sloping position at around 45° angle. Once lifted, a difference can be created between the water levels on both sides, while the Delta Works in the Netherlands are provided with hydraulically driven, closable doors that are moved up and down vertically.”
The large concrete barrier caissons are placed with great accuracy by means of a special designed pontoon. To place these barrier caissons, HydrauRent designed 14 winches with a pulling force of 80 ton. Ten winches to position of the vessel and four winches to place the caissons. “We are rather proud of the fact that we were able to contribute to this large-scale project, which will protect an important Italian heritage against the water.”
The fourteen 80-ton winches that will transport and position the giant concrete foundations of the water-retaining structure have been fully designed, manufactured and tested in-house under the supervision of Lloyds Register. “The winches are suitable for mooring and hoisting activities in the offshore and maritime industries and have a nominal pulling force of 80 ton. To develop these specific winches, we have carried out extensive calculations and analyses. And to check the drive, brakes and complete construction, the winches have been tested in the Hydrauvision premises under a load of more than 100 tons.”
“Begin 2013, we received the order from GLF to deliver these winches, including the corresponding powerpacks. Within five months, 14 winches had to be produced and tested. Quite a challenge! Supported by the finite element method (FEM), the necessary constructive parts have been produced under Lloyds Register certification. In the meantime, MIP Yerseke, one of Hydrauvision's other subsidiaries, constructed the piping. Subsequently, all parts were assembled in Schoondijke. The basis was formed by HydrauRent's standard winch, driven by four hydraulic motors for each winch and a geared transmission. Thanks to this construction, the winches could be delivered in a very compact form and within a very short time. Finally, the winches were painted to endure offshore circumstances and the hydraulic part was given an extra anti-corrosive treatment."
The test bench used for the load test was also developed by Hydrauvision. Lloyds Register checked and certified the whole testing process. “Also the hoisting points in the construction and the spreader bars used to transport the winches, including the winch cable, were fully tested under the offshore standard of DNV 2.7-3.” Subsequently, the winches were paid up with 48 mm cables, under a pretension of 20 tons pulling force. The tensioner needed for this has also been developed in-house by Hydrauvision. It is used to wind up cables with various diameters under a pretension of 6 up to 30 tons for various winch applications. The Italian counterpart of Lloyds, RINA, has adopted the Lloyds Register certification.
'Customised rental services'
The transport to Italy and installation of the winches on location was accompanied by people from Hydrauvision and HydrauRent, who brought their own mobile work containers to install and commission everything on location, including the piping on deck. Because every mooring point needs two lines, a pair of two winches need to be placed close together. To keep the gravity point of the pontoon as low as possible, the mooring winches were placed behind each other, with each drum provided with a shield to divide the drum in a part for the wire and an empty part. Thanks to this construction, two winches can be placed in a row, whereby the cable of the rear winch runs through the ‘empty’ drum side of the winch in front. This way, the necessary capacity was obtained in a very compact way. After the job will be done, the partitions will be removed, returning the winches to their original, standard, 80-ton versions. The winches have also been equipped with a considerable amount of electronics. The combined production and use of mechanical parts and electrical parts (mechatronics) makes it possible to integrate the winches in an all-over operation and monitoring system. The mechatronics for these winches are developed in house by Hydrauvision. “This way, HydrauRent has done justice to its speciality ‘Customised rental services”.