the vessels have a glass fibre hull and are amongst the largest vessels built in this material. they are equipped with hydraulic machinery, and its engines are placed in the aft part of the superstructure. the engines are separated from the hull with rubber springs. the engine power is transferred to the propeller unit (which can turn 360 degrees) through two separate hydraulic valves; in this manner the vessels are as quiet as possible, and it has been possible to completely eliminate propeller axles, which are very difficult to silence and are easily damaged in mine explosions.