How does a retractable tunnel system work exactly?

With shallow draught there is a possibility the propeller of a vessel cannot completely be covered in water, which results in increased resistance and reduced velocity. This is when the Flex Tunnel comes in. The Flex Tunnel is a retractable tunnel system, constructed in the aft of a vessel hull. The airtight seal of the tunnel onto the nozzle creates vacuum, ensuring sufficient water flow to the propeller. Hereby the effective operation of the propeller remains guaranteed, even in shallow waters with minimal cargo.

But when a ship is loaded and navigating in deep waters, the Flex Tunnel can simply be retracted and embedded into the vessel hull. In this situation, the water flows into the propeller unobstructed. As opposed to a fixed tunnel, the flexible retraction of this system significantly reduces the overall resistance of a vessel. It allows the captain to choose when and where to set the tunnel into or out of operation.