In 1981 Wärtsilä (Turku, Finland) was commissioned the construction of three large catamaran type crane vessels. In the design of the vessels the determination of the wave loads acting on, and the strength of the bridge structure connecting the hulls received considerable attention. They were subject of a thorough investigation in the course of which theoretical calculations and model tests were performed at MARIN (formerly NSMB) in Wageningen, The Netherlands. The paper describes the design procedure for the bridge structure, which is based on a probabilistic approach. It also highlights some typical results of the calculations and tests.
In the late seventies Wärtsilä received a technical inquiry for a large catamaran type crane vessel from Sudoimport on behalf of the Ministry of Gas Industry of the USSR. A detailed inquiry in 1980 was followed in 1981 by a contract for a series of three vessels. In 1984 a fourth vessel was ordered. The first ship was delivered in 1984.
Before and after the signing of the contract design work and research was carried out. In the course of the investigation theoretical calculations and model tests were performed. Attention was paid to various hydrodynamic aspects of the vessel such as resistance and propulsion, manoeuvring and especially the motion characteristics in waves.
One aspect of the design, the hydrostatic and hydrodynamic loads in the bridge structure connecting the hulls, received special attention. In this paper the method used to determine design loads and the results of theoretical calculations and model tests will be discussed.
The special type of vessel was selected by the owners, who have experience with catamaran crane vessels operating in the Caspian Sea [1]. The type has certain operational advantages which single hull crane vessels lack, for instance:
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wide working deck for operations and transportation;
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shallow draft;
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large hydrostatic stability eliminating the need for heel compensation systems.
An additional advantage for the owners resides in the fact that the two hulls and the bridge structure can be prefabricated and transported separately to the Caspian Sea for final assembly.
A general arrangement of the vessel is shown in Figs. 1 and 2. The main dimensions are shown in Table 1. The Kone-Gusto revolving crane is designed for a 600 tonnes lift at an outreach of 39 m, see Fig. 3 and Photo 1.
The maximum speed of 11.S knots, combined with the large deck area make the vessel very suitable for the transportation of construction modules.
The vessel is designed for worldwide operations.
Since the vessel is the largest in the world today, since no standard design methods and rules were available and since the vessel was the first of its type to be built by the yard a comprehensive research effort was started. The rules of the USSR Register of Shipping offered no stringent guidelines for the design of the bridge structure, therefore the yard had to decide on a design philosophy.