Friday, April 15, 2016

Danish firm creates innovative container feeder ship designs





Danish naval architecture firm KNUD E. HANSEN has developed several container feeder vessel designs, according to a company statement. Each design presents a series of innovations as part of a solution tailored to specific requirements.

The first of three designs relates to a 2000-TEU vessel designed to call at small, narrow, up-river ports, such as the Port of Bangkok in Thailand. Navigating such harbors requires a shallow draught – in the case of Bangkok, no more than 27 feet.

Such a vessel needs a relatively small diameter propeller. To accomplish this without a loss of power, company designers presented a special propeller arrangement using a directly driven main propeller with a diameter of 19 feet and a counter-rotating Azipod with a 15.4-foot propeller.

"The dual arrangement makes up for the relative small diameter of the propellers," said Jesper Kanstrup, Senior Naval Architect at KNUD E. HANSEN. "The total propeller disk area of the two propellers corresponds to the area of a single propeller with a diameter of approx. 7.4 m and further, the counter-rotating propeller will recover some of the swirl energy produced by the main propeller, which increases the overall efficiency."

A second design envisions a ship with a 3,800-TEU capacity that doesn't require such a shallow draught. This design sees the feeder vessel equipped with a larger diameter, slower-turning propeller. "With the large propeller we get a propulsion efficiency which is not that far from the efficiency of a counter-rotating solution, but for a much lower cost."

Unlike most feeder vessels, the deckhouse of this vessel is positioned slightly forward of amidships to

maximize the number of container slots on deck considering the IMO requirements to the line of vision from the bridge. The added number of slots can be utilized in real-life loading conditions because the vessel is wider and has a higher stability than most feeder vessels of this size.

This arrangement prepares the vessel for LNG and dual-fuel propulsion – a square block below the deckhouse means the ship can easily be retrofitted for either HFO tanks or LNG tanks.

The third arrangement features an innovative hull shape suited for carriage of both partial and full container loads.

A vessel behaves differently based upon its load. A large container vessel, when carrying few containers, offers shallow draught, but has so much stability that accelerations are too high, causing problems for the lashing gear and the crew.

"In this situation, you don't want anything more than sufficient stability and so a narrow hull is preferable," says Kanstrup. "The problem being that, when you come to carrying a full load you require a wider water line for additional stability. So the ideal hull would have inclined hull sides with narrow water lines at shallow draught and wider water lines at deeper draughts, which, however, is not the most practical design considering the vertical quays in ports."

In this case KNUD E. HANSEN created a hull with inclined sides, mirroring the triangular sections on each side to create a trimaran or a "stabilized mono-hull" with a narrow main hull with vertical sides and outrigger hulls with a triangular cross section, but vertical sides towards the quay.


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