Innovation in ship conversion

RINA has classed the last two Concordia ships designed specifically to transport heavy wind power components around Europe. The two ships, “Rotra Vente” and “Rotra Mare”, confirm the trend towards highly specialised vessels designed to perform particular tasks with the utmost efficiency.

These sister vessels were originally built as container ships and repurposed using many innovative features. “Rotra Vente” is designed to carry turbine housings (nacelles), while “Rotra Mare” will transport wind turbine towers and rotor blades.

Modifications include the removal of cargo hatch covers to create a flush main deck of 2,000sqm. Cargo holds were transformed into ballast tanks, support structures and void space.

The challenge of loading and unloading heavy components was solved by self-propelled modular transporters with multiple wheels. The vehicles roll onto the deck via a bow ramp, making the loading process more cost-effective and independent of both crane infrastructure and wind conditions. A hydraulic system extends the adjustable ramp from the bow to the quay.

A single nacelle weighs about 430 tonnes, so to avoid heeling during cargo operations, an automatic touchscreen-controlled heeling tank system has been installed. A manual forward/aft trimming system controls trim variations.

Ro-ro vessels are required to have a watertight compartment at the bow. This normally consists of a bow door and watertight door a few metres apart. On the “Rotra Vente” and “Rotra Mare”, the whole forecastle is a watertight compartment that is lifted into place by hydraulic cranes and locked into position. Anchor pockets were shifted back and outwards.

Since this new design does not appear in the International Convention on Load Lines (ILLC), the Dutch Administration granted an exemption. The exemption was based on a “novel design” proposal presented by RINA, which was considered to have the same safety level as the convention’s original philosophy.

Energy-saving measures included reblading and optimisation of the propeller for a lower trading speed of 15 knots. This reduces power demand by 14 percent and offers a return on investment of less than a year.

In keeping with their innovative features, the ships have a modern look and feel. Completely overhauled, the wheelhouse of the “Rotra Vente” features 46-inch LCD displays.

As a container ship, “Rotra Vente” was just a bare hull that was never outfitted. Through extensive non-destructive testing and fatigue life computation, RINA succeeded in classifying the ship as a new building, with a keel laying date at the beginning of the conversion works.