Finnpusku is an integrated tug and barge system owned and operated by ESL Shipping, a Finnish shipping company that specializes in bulk cargo transports in the Baltic Sea. The system was developed in the 1980s by Finnlines, another Finnish shipping company that also managed the vessels until 2003, in co-operation with Rautaruukki to transport raw materials to the Raahe Steel Works. Two pushers and five barges, four of which remain in service, were delivered by Hollming in 1986–1987.
Today the Finnpusku system consists of pushers Rautaruukki and Steel, and barges Board, Botnia, Kalla and Tasku.
Concept
Separating the expensive machinery section from the cargo space offers several advantages in comparison to conventional vessels, one of the most important being the ability to operate on the "drop and swap" principle which minimizes the turnaround time in port for the pusher and its crew. When a pusher-barge combination arrives at a port, the fully laden barge is left for unloading while the pusher picks up an empty one and leaves again. In theory the system works on optimum efficiency when there are as many barges as there are pushers and ports of call – the barges are always either being loaded or unloaded, or underway with a pusher. In addition to reducing unprofitable waiting time such operation principle allows more time for the unloading of the barge, removing the need for expensive cargo handling equipment in the unloading port.Eriksson, U. Puskuproomujärjestemä. FG-Shipping Oy Ab, 1991.
One of the major arguments in favor of integrated tug barge systems is the small number of crew required to operate such vesselFINNPUSKU - Finnish tug/barge combination boosts Raahe iron works' sea cargoes. The Motor Ship, December 1986, pages 40–42. — whereas a conventional vessel with capacity in par with the Finnpusku pusher-barge combination would require a crew of 16–17, the integrated tug-barge unit can be operated by a crew of only 9. In some cases an integrated system is adopted only for this reason and the pusher is rarely, if ever, decoupled from the barge.
An integrated system has several technical advantages in comparison to towed barges. Traditionally tugs, being short in length, have to operate at relatively high Froude numbers resulting in high wave making resistance and the barges, being towed in the tugs' wake, have skegs that improve directional stability but increase drag. Positioning the tug behind the barge in a stern notch improves the hydrodynamic efficiency of the combination, resulting in significant reductions in the total resistance. In addition the tug, operating in the wake of the barge, has better control over the combination and thus improves seaworthiness and maneuverability in comparison to the traditional towing arrangement.van Leeuwen, W.A. Tug/barge systems - An economical alternative for the short-sea . Schip en Werf de Zee, 4-92.
Integrated tug barge systems are generally divided into three generations by the type of coupling. In the first generation systems the tug is connected to the barge by wires or chains. However, because the two vessels are subject to different motion responses due to their shape, displacement and position on a wave, such operation is only possible in calm sea conditions — in rough weather the tug has to disconnect from the barge and continue the journey by towing it in a traditional way. The second generation systems are designed with a deeper stern notch and improved coupling devices to allow operation in heavier seas while still permitting relative motion between the two vessels. The third generation systems such as the Finnpusku system, equipped with rigid or articulated mechanical coupling, allow operation in all sea states and even in ice conditions as the pusher-barge combination behaves hydrodynamically like a conventional ship. However, in some cases the specialized hull form of the pusher, designed to form a streamlined hull when coupled to the barge, might lead to problems with stability and seakeeping when the pusher is operated independently.Integrated Tug Barge (ITB) / Tug/Barge Unit (TBU). GlobalSecurity.org.
Development and construction
The history of the Finnpusku integrated tug barge system dates back to 1964 when Rautaruukki started steel production in the new steel mill in Raahe, Finland, and began supplying the factory with ore concentrate, coal, coke and other raw materials.von Bruun-Riegels, U. Raaka-ainekuljetukset proomuilla. Rautaruukki Oy, 1991. Around the same time the Finnish shipping company Finnlines researched transporting cargo by barges and developed the first version of the Finnpusku system, but due to problems in funding and the devaluation of the Finnish markka in 1967 the idea was not pursued further. However, an upgraded concept was developed in the 1970s.Holma, H. Proomukuljetukset. Oy Finnlines Ltd, 1972.
By the end of the 1970s it was realized that as the iron mines in Finland would soon be exhausted and there would not be enough suitable ice-strengthened tonnage to guarantee a continuous supply of raw materials for the expanding steel works. The draught of the bulk carriers available in the market exceeded the water depth of the port of Raahe and unloading the ships would have required a large number of cranes. While transporting the raw materials by barges proved to be feasible as they had low draught and could be unloaded with wheel loaders, towed barges could not be used during the winter and their poor maneuverability made them unsuitable for the confined waterways. For this reason it was decided to investigate if it would be possible to design a pusher-barge system that could also be operated in ice conditions.
When Rautaruukki consulted Finnlines that already operated the steel company's conventional bulk carrier Rautaruukki, the shipping company immediately presented the integrated tug barge system it had developed in the 1970s, the Finnpusku system. A development contract was signed and Finnlines performed several feasibility studies which showed that a pusher-barge system would be the most economical and efficient method of transporting bulk cargoes on the relatively short routes of the Baltic Sea. Thanks to the extremely short turnaround time at ports, the service speed of the vessel could be lower than that of normal ships, resulting in lower fuel expenses.
The initial plan was to establish shipping companies for each vessel under the joint ownership of several large Finnish industrial and shipping companies, including Rautaruukki and Finnlines, that would own and operate the Finnpusku system. However, due to delays in negotiations Rautaruukki, concerned about the continuous supply of raw materials to the Raahe Steel Works, decided to order one pusher and two barges for itself and signed a building contract with Hollming on 29 September 1984.A revolutionary pusher-barge system. Navigator 1985. A follow-up order for another pusher and three more barges was signed on 14 March 1985 by joint shipping companies formed by Effoa Oy (20%), Oy Finnlines Ltd (16%), Hollming Oy (10%), Neste Oy (25%), Palkkiyhtymä Oy (10%), Oy Paratug Ltd (5%), Rautaruukki Oy (9%) and Thomesto Oy (5%). All vessels were managed and manned by Finnlines.
While the pushers were built completely in Finland, to reduce the building costs the steel work of the barges was subcontracted to a Portuguese shipyard Estaleiros Navais de Setubal in Setúbal, from where they were towed to Hollming for outfitting.Mauno, J. Finnpusku minimoi satama-ajan. Navigator 11/86. The total price of the Finnpusku system was FIM 300 million (US$61 million). The first pusher, Rautaruukki, and two barges, Kalla and Tasku, were delivered to Rautaruukki on 31 October 1986 and the second pusher, Finn, and barges Baltic, Board and Bulk to the joint shipping companies "Puskija", "Proomu I", "Proomu II" and "Proomu III" on 28 April 1987.Finnpuskut valmiit. Navigator 9/87. It was estimated that the two pushers and five barges of the Finnpusku system would carry one third of the ten million tons of bulk cargo arriving in Finland by sea every year.
Technical details
Combination
A Finnpusku pusher-barge combination consists of one pusher vessel and one barge. The overall length of the combination is and its breadth and draft at summer load line are that of the barge, and , respectively. However, in the brackish water of the Baltic Sea it can be loaded to a maximum draught of . During ballast legs the pusher maintains its normal draught while the barge is ballasted to a draught of to reduce the displacement from 20,930 tons to 17,630 tons. In such loading condition the main deck of the barge is at the same level with the pusher's gunwale.Pusher Vessels and Barges . ESL Shipping Oy. The tonnage of the combination is that of the pusher and barge combined, , and .Vapalahti, H. Finnish illustrated List of Ships 1999. Judicor Oy, 1999.
The combination is classified by Det Norske Veritas with a class notation of +1A1, Pusher/Barge Unit, Ice IA+. It has the highest Finnish-Swedish ice class, 1A Super, which means that it is designed to operate in difficult ice conditions mainly without icebreaker assistance. Thanks to the icebreaker bow and sloping sides, the combination could operate independently in level ice. When the Finnpusku system entered service in the mid-1980s, its icegoing capability was superior to most conventional bulk carriers.
Finnpusku uses a unique rigid coupling system, Wärtsilä Marine Locomotive, which consists of two hydraulic locking pins, one on each side of the pusher, and one fixed pin in the bow. When connected, the hydraulic pins exert a transverse force of 450 tons to the sockets, forcing the jaws of the barge apart by , and the angled faces of the coupling pins push the pusher forwards, resulting in a longitudinal force, also of 450 tons, at the bow pin. The three-point connection removes all degrees of freedom and results in the combination behaving hydrodynamically like a single ship, allowing unrestricted service and independent operation in the severe ice conditions of the Gulf of Bothnia. The pusher can be connected to the barge at three different levels, removing the need to ballast the barge to the same draught as the pusher when not carrying cargo. In addition to mechanical coupling the pusher is connected to the barge by several electrical cables on the starboard side and flexible pipes on the port side. The latter allow the pusher's fuel and freshwater tanks to be topped up from the much larger storage tanks of the barge.Puskija FINNin ja proomu BALTICin kaatuminen Hangon edustalla 27.12.1990. Suuronnettomuuden tutkintaselostus n:o 2/1990. Onnettomuustutkintakeskus. Helsinki, 1992.
The combination of a pusher and a barge is usually referred to by using the names of both vessels, e.g. Rautaruukki-Board.
Pushers
Initially there were two pushers in the Finnpusku system, Rautaruukki and Finn, built by Hollming in 1986 and 1987, respectively. After capsizing in 1990 Finn was rebuilt and returned to service as Steel in 1991.
In 1991 Herakles, a salvage tug built in 1967 and owned by Finnish towing and marine salvage company Alfons Håkans, was converted to a pusher and chartered to Rautaruukki as the third pusher of the Finnpusku system. After the conversion Herakles was chartered to Rautaruukki and continued to operate as part of the transport system until her demise on 3 March 2004, when she sank with the barge Bulk near Swedish Grundkallen lighthouse in the Bothnian Sea.
Rautaruukki and Steel
Main articles: Steel (pusher) and Rautaruukki (pusher)
The pushers of the Finnpusku system are long and have a breadth of at the waterline and at the bridge wings.STEEL . DNV Exchange. The draught and depth to upper deck, and respectively, are the same as those of a fully laden barge.