Expanding the World’s Largest Heavy-Lift Ship

“The call came just a few weeks before Christmas,” recalls Pieter de Boer, Lead Engineer and Commercial Manager at Iv. “Boskalis asked if we could urgently deliver a design to widen the Vanguard. They needed to transport a floating dry dock that simply wouldn’t fit between the caissons (the towers you see on the ship). So, the Vanguard had to be made wider, and fast.” The pressure was high. “Boskalis wanted to order the required steel within three weeks. We immediately contacted Nevesbu and formed a joint team. Their expertise in naval architecture was indispensable.”

Making a giant even bigger

The BOKA Vanguard is globally recognised as a leading vessel in the heavy-lift shipping industry. Edo Donkers, Design Manager at Nevesbu, explains: “The Vanguard is a semi-submersible heavy transport vessel: a ship capable of carrying cargo larger and heavier than itself. It features a flat deck without a bow, an open stern, and caissons with massive ballast tanks that allow it to submerge in a controlled manner.”

Originally measuring 275 metres in length and 70 metres in width, the Vanguard was already the largest vessel in its class. “Picture three football pitches, that gives you an idea of the scale”, says Edo. But even that wasn’t enough. As the maritime industry continues to grow, so must the Vanguard. “Our challenge was to extend the deck to 100 metres, enabling the transport of exceptionally wide cargo such as floating dry docks and FPSOs.”

Shifting the outriggers

For Pieter and Edo, working on the widening of this iconic vessel was a unique experience. “Boskalis handled the construction themselves”, Edo explains. This took place at a yard in Zhoushan, China. “Our task was to deliver the engineering. Boskalis already had a concept:  shifting the port-side outriggers outward to create more space between the caissons. We had to make that concept feasible, safe and effective. We began by modelling the ship in 3D and identifying the load-bearing structures.” Pieter adds: “That’s crucial. You need to know where new elements can be attached without compromising the vessel’s structural integrity.”

No room for error

The complexity in this project was the combination of speed and precision. With drawings and calculations due within three weeks, there was no margin for optimisation or mistakes. Everything had to be right first time. Edo explains: “We designed three different outrigger variants; at the bow, port aft and starboard aft. Each had its own shape and specific requirements for load and integration. In effect, we created three unique structures to move the caissons outward, together forming the ship’s widening.” The added sections – totalling 1,600 tonnes of steel – also required openings to allow water ingress during submersion. “They couldn’t add buoyancy to the vessel.”

Zero risk allowed

“You cannot simply add structures to a vessel of this scale”, Pieter explains. “Above the waterline it’s enormous, and below it’s like a four-storey building. You constantly ask: if we place a wider outrigger here, what does that mean for the entire structure and the loads involved? Given the dimensions, the outriggers form an integral part of the vessel’s overall structure. Altering them affects everything, from sailing characteristics to safety during submersion. Because the design had to be completed within such a short timeframe, we designed a structure entirely from steel plates, meeting stringent maritime standards.”