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Dykstra designers go where no one has gone before

January 5, 2013 by robert in Featured, NL Excel with 0 Comments

AMSTERDAM _ The 103m Pretoria sank in a vicious July storm on Lake Superior off  Wisconsin in 1903, 5 years after she was launched. The solid wooden barge _ and 5 others of that era and length _ are remembered as design flops proving the limits of wood’s usefulness for hulls. What brought the Pretoria to mind at the Amsterdam offices of Dykstra Naval Architects in 2010 was a request to work on the largest sailing yacht in the world that would also be the world’s largest wooden ship ever built. At an eye-popping 141 meters _ 38m longer than the Pretoria _ the Dream Symphony is to be launched in 2016 off the Dream Ship Victory yard in Turkey. A 4-masted staysail schooner, she will have an 18m beam, an 8m draft, a displacement of 4,500 tons and sails that can cover a soccer field!

Dykstra has in recent years worked on 3 smaller, all-wood yachts, from 42m to 65m. But the Dream Symphony is an enterprise of Star Trek ambition. It has the company designing boldly where no man has designed before. Clearly, there is no off-the-shelf  when you build a 141-m sailing yacht. That is because global certification rules cover yacht building values and criteria for wooden sailing vessels of up to 50m only. “Anything bigger and you need to come up with your own design solutions, do your calculations and tests,” says Dykstra naval architect Hilbert ten Have.

The Pretoria’s death knell was solid wood’s structural weakness. At a hull length of 100 or so meters there is no amount of steel plates, arches and straps to fix wood’s structural flaws and maintain sea worthiness. For the Dream Symphony’s hull, Dykstra relied on the TNO technology institute in the Netherlands and Italy’s Messina University to do extensive stress tests of solid and laminated wood. The latter offers a higher degree of hull stiffness. A defect in one ply will not cause the entire laminate to fail whereas a flaw solid wood can weaken large pieces. In the Dream Symphony, the grain of wood plies will lie in different directions creating a stiffness that radiates in all directions.

Laminated wood is common in yacht building, but unprecedented on a 141m hull. Dykstra designers need to know if at that length laminated wood can be made strong enough to take global loads. Can it be made stiff enough in bending and torsion. Providing structural design support in the Dream Symphony project, SP-High Modulus _ part of Gurit Holding AG, a Swiss maker of advanced composite materials _ uses Finite Element Software. It analyzes strains and stresses on every ply of Iroko at any location on the Dream Symphony’s massive hull. It also calculates the toll of wave slamming. By late 2012, the Dream Symphony project was en route to meeting minimum load and stress norms. Still, more work is needed, including important detailed structural engineering.

The Iroko of the Dream Symphony hull will be of durably grown timber from managed forests. It will be covered by an 8mm outer sheet of glass fiber. Ten Have: ‘’Iroko has good strength properties for its weight. And it holds form well.” Dykstra has to date worked on more than 50 projects, including 26 big yachts _ most notably the Maltese Falcon and its revolutionary dynarig.

“But this is a very exciting project that explores new frontiers in the design of sailing yachts,” Ten Have says of the Dream Symphony project.

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