Alta / Oksoy Surface Effect Ship (SES)
The focus on 180-foot Surface Effect Ship (SES) catamarans with glass fiber hulls was initially hailed as a technical breakthrough, but major problems with the propulsion, budget disputes and missing money for spare parts quickly made the prestigious project an embarrassing and expensive affair for all involved. The five Alta class Surface Effect Ship (SES) are coastal minesweepers, while the four near-sisters of the Oksoy class are minehunters. Mine Countermeasures involve minehunting and minesweeping. Minehunting is classified as the systematic detection and elimination of mines one at a time. Minesweeping is the clearing of a pre-defined area, eliminating whatever mines may be deployed there.
By 2018 the Navy had six mining ships, three miners (Altaklassen) and three mining vessels (Oksøyklassen). The vessel has the task of halving national and international waters free of mines. As a rule, the Navy has a mining vessel in NATO's standing mining force. The vessel cooperates closely with the Minedrive command in operations that include mining and explosion cleaning.
The vessels were manufactured by Kværner Mandal early in the 1990s and handed over to the Navy between 1994 and 1997. The vessels are equipped with weapon and sensor systems to detect, identify, classify and destroy marine mines. In addition, they are equipped with some smaller weapon systems for naval defense.
When KNM Oksøy had her maiden voyage in 1994, she was the Navy's prestigious project and the pride of defense full-packed with high technology and among one of the world's most advanced vessels. Both catamarans, hydrofoils and hovercraft are built to lift the most of the vessel from the water. To push large-scale vessels through water are energy-intensive, but by lifting most of the craft up the water, less forces to create momentum. It makes it possible to keep high speed. Catamarans resting on a pillow of air were no new idea. The Americans did attempt in the 1950s, but without success with the heavier materials of the day.
Only when composits were on the market was the road open to larger hovercraft. Thus in 1989, the Navy had decided that the new mine sweepers would be hovercraft. The technology not only made it possible to achieve high speed, but the air cushion also dampens the shock wave from an underwater explosion by up to 60 percent. The air pit thus protects the crew and saves potential life if the boat triggers a mine. Lifting the vessel up of the water also reduces the boat's acoustic signature. This means that the mining and coastal corvettes do not sound like mine or coastal ships for those who listen to foreign vessels. The boats sound more like a rain shower. During tests, it has been difficult to capture the sound of these big boats when other small boats are close by.
Centrifugal fans are one of several types of fans, which amongst other things are especially suitable for use as lift fans for hovercraft. Larger centrifugal fans are generally constructed of metallic materials, such as steel, acid-proof steel or aluminium. These fans typically have a very high rotation speed that generates enormous centrifugal forces, corresponding to 1000-4000 times the gravitational acceleration on the fan blades. The fan construction must therefore be extremely robust to enable those great forces to be absorbed in the structure.
For use in military vessels there are also requirements regarding magnetic signature from the vessel and its systems. Rotating metal structures, for example, produce a disturbance in the earth's magnetic field that can be intercepted by special sensors. It is therefore vital that fans produce minimal electrical eddy currents. This is solved by using materials with low electrical conductivity in the construction of the fan, where in addition each individual part is electrically insulated from the others. Existing designs of centrifugal fans in composite have employed an unsatisfactory method for attaching the blades to side disc and centre wheel, whereby substantial shear forces are generated in the bolt connection. This has resulted in a short service life and also several cases of fan breakdown.
Mandal developed a robust centrifugal fan which is entirely or partly made of composite materials and which avoids the above-mentioned disadvantages related to the attachment/removal of the blades and at the same time provides correct load transfer from the blades. It is a further object to obtain a centrifugal fan with a low magnetic signature. Furthermore, the centrifugal fan according to the invention has a low moment of inertia, thus enabling start-up of the fan to be implemented without a complicated coupling and/or gear device between fan and drive motor.
The news that Mandal won the contract on nine ships to be used for mining and mine sweeping was received with jubilee. The agreement with the Navy would create hundreds of new jobs. It was popular in a region which for several years had struggled with high unemployment. Mandal won because it was possible to document high skills, but also because the offer was significantly lower than competitor.
It became clear that the price differential was so great, and in retrospect this was seen in connection with that the project incurred exceedances. The old boatyard at Vestnes had certain limitations both in terms of width and depth, and therefore decided Kværner Boat Service to build a new yard on Gismerøya. Construction work started immediately after the award of the contract, at the same time as the engineering work among the engineers still on Vestnes. When the new yard was finished it was a state-of-the-art facility, the foremost in the world of its kind. Gismerøya was officially opened in December 1990 by the Defense Minister Johan Jørgen Holst. In 1991 Kværner bought all the shares and baptized Kværner Boat Service to Kværner Mandal. The main task was to commence production of mining vessels.
Early on it became evident that the engineering tasks were underestimated and would take more time than expected. Delayed passports for a company that already had hundreds of employees waiting for the final drawings to come in production. In 1993, the project was delayed 18 months, and the Navy threatened to suspend payments. But after the management and they employees mobilized political support, and project managers on both sides were exchanged to create a better cooperative climate, a revised progress and financing plan was adopted. The yard and the state agreed to divide the bill overruns.
There was pomp and splendor on Gismerøya when Queen Sonja came to Mandal to baptize KNM Oksøy on March 24, 1994. Finally, the boat was launched and ready for service! KNM Oksøy, 55 meters long and 390 tons heavy, was built for a cruise speed of over 20 knots and the capacity to go twice as fast if it had to, and the conditions add to it.
The Norwegian series was the only one in the world with two blowers. It makes them roll a little, which is a big advantage in the pursuit of mines. A quiet platform makes it easier to find mines.
In the next few years, Kværner Mandal produced an average of two vessels a year. The ninth and last was delivered August 8, 1997. After Kværner and the State agreed on the revised refinancing plan, the project kept both delivery plans and budget. The technical quality of the boats was very good. Chief of Defense, Kontmirmiral Hauger-Johannessen, told the Fædrelandsvennen that "we have had excellent vessels, which have been the best in all exercises with our allies."
According to the Navy, the boats will be phased out in 2027, but some think that will not happen. They are simply too good. Next generation boats will be autonomous and unmanned.
The two mining vessels KNM Oksøy and KNM Glomma only got 10-12 sailing days behind them before they were put in reserve at Haakonsvern. The mining project exploded with a cost overrun. Thus, there was no money left for spare parts for the vessels. Two vessels had to be sacrificed to make the remaining seven mining vessels spare parts. In 2003, the Storting decided that Oksøy and Glomma should be phased out. Later, all electronic equipment and motors are picked out. Thus only the hulls were left of the proud navy vessels. By 2009 the defense hoped to get half a million for each of the hulls that the port authorities in Copenhagen and Stockholm consider buying. The military removed the engines and used spare parts from the vessels, otherwise the boats are in good condition. The boats have kitchens, canteen and beds for 40 people on board.
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