Morocco’s recent order for three Sigma multimission frigates from Schelde Naval Shipbuilding confirms the value of the ships’ modular-hull design, executives say, and opens the door to further export sales of corvettes, frigates and patrol vessels built with it.

Morocco ordered three multimission frigates from Schelde that use the shipbuilder’s Sigma modular hull design. Credit: SCHELDE CONCEPT

The Royal Moroccan Navy signed the contract with Schelde on Feb. 6 (DTI March, p. 8). Worth approximately €510 million ($816 million), it calls for the design, build and delivery by 2012 of three surface combatants that the Moroccans are designating multimission frigates.

“This is an important development for us because it signals that the Sigma concept has merits,” says Hein van Ameijden, director of Schelde Naval Shipbuilding, which is located here. Four missile corvettes built with the Sigma design have been sold to Indonesia, but van Ameijden says some observers dismissed the deal as just another case of an old colonial power selling defense equipment to a former possession.

The Sigma design uses standard, 7.2-meter-long (24-ft.) sections separated by bulkheads with watertight doors throughout the ship. By varying the number of sections, a ship can be stretched or shortened. The Indonesian corvettes, for example, have 12 sections; two of the Moroccan ships have 13, and the third Moroccan ship has 14.

The length of the sections was set at 7.2 meters because of an international requirement that 6-meter-wide damage be survivable, says Schelde Naval Architect Leon Goossens. “Based on the 7.2-meter-section principle, such damage will result in a maximum of two sections being flooded, which is survivable.” The section dimensions also provide an extra margin to accommodate standard 20-ft. containers.

Van Ameijden says Schelde is “very much aware” of the “90:10 rule” of shipbuilding: Changing 10% of the ship requires changes to 90% of the drawings. This, he adds, is not necessary with the Sigma concept because of the high degree of standardization.

The standard-section-length principle enables Schelde to incorporate standardization within beams, doors, portals, stairs and other key construction components, saving cost and making design, engineering, purchasing and production more efficient. The interfaces between the compartments in the ship are also virtually identical, Goossens says.

Schelde has a preferred supplier base, including Imtech for the platform systems and Thales for combat systems, which helps to further reduce cost (although customers can select other vendors).

“That we were able to respond quickly to the Moroccan opportunity is mainly due to the Sigma concept and the hull-model testing done earlier,” says van Ameijden. “In simple terms, we just had to pull out the drawing, cut and paste a bit, and the new configuration was ready. The concept is modular in philosophy, comprising the whole ship instead of just modular equipment containers that can be dropped in here and there. Our concept has been extensively tested and proven at sea.

“Indonesia selected the Sigma design because it was the best, and so did Morocco,” he says.