By David Wagman
Managing Editor, Power Engineering
As companies search for ways to keep costs low and stay competitive, the shipping industry has met the challenges of shipping expensive, large and sensitive power plant parts from the factories to the destination's ports.
Dockwise Shipping is a Netherlands-based shipping company with a fleet of 15 semi-submersible heavy transport vessels (HTV). The vessels are used to ship fully-erected cargo, which allows fabricators to build units in cost-effective countries. The current maximum load that can be shipped is over 70,000 metric tons (154 million pounds). Most cargoes shipped by Dockwise are much smaller but still require significant engineering to make the transportation feasible.
After the stability of the ship-cargo combination has been checked and the transportation route has been laid out, engineers determine the design environmental conditions for which the transport has to be designed. Elements such as wave height and wind speed parameters serve as input for calculations that model the expected motional behavior of the ship. The motions and accelerations finally define the amount of external sea fastening and eventual internal reinforcements in the cargo that are required to make the trip safe and successful.
For the power industry, several power barges and fuel barges have been shipped by Dockwise. These barges are loaded onto the HTV by submerging the HTV, floating the barge over the deck and then deballasting the HTV. The cargo rests on a layer of soft wooden cribbing beams, positioned under the strong parts of the cargo, such as bulkheads, web frames and stiffeners. If a cargo is non-floating, such as heat recovery steam generators, it can be rolled, skidded or lifted onto the HTV deck.