New materials to improve the safety of high-speed crafts
UPM researchers have developed a new technology based on composite materials and viscoelastic layers that improve the resistance of hull of high-speed crafts what makes them safer.
High-speed crafts glide on water hitting the hull against the surface. This provokes significant damages that compromise the high-speed crafts resistance and thus its safety. A group of researchers from Universidad Politécnica de Madrid (UPM) proposes a new manufacturing system that inserts, among the layers of composite materials to build the hull, a thin viscoelastic layer that absorbs and fades the energy caused by the impact on the water surface.
The tests show that the frequency of repair of damaged hulls when using this new system can be three times less. Besides, this system cannot only extend the useful life of the high-speed craft but also the safety of the people on board.
Unlike other vessels, such as displacement ships, whose movement on the sea is based on its separation from water there are others whose design allow them to glide on the water surface and move at great speeds since they do not need to displace large bodies of water as they navigate. These boats are supported on the stern and the bow rises sequentially to fall shortly after impacting strongly on the surface of the water.
As the water behaves like a wall at such high speed, the vessel crashes against it again and again. This phenomenon is called slamming and is a serious issue in vessels that move at medium and high speeds.
The cyclic slamming can provoke significant damages in vessels, especially when they are made of composite materials such as inorganic fibers (glass, carbon) and agglomerate polymers (polyester, vinyl ester or epoxy). These composite materials are light but also more sensitive to impacts than the metallic materials traditionally used in this type of vessels (steel, aluminum).
During the short period of time between the start of the impact and the separation of water around the vessel, the strain supported by the material grows rapidly and the deformation speeds imposed are very high. Under these conditions, the material responds with a fragile behavior and internal micro-tears.
In order to protect the structure of high-speed crafts, researchers from School of Naval Architecture and Marine Engineering have developed a new system that introduces a thin viscoelastic layer among the layers of composite materials to build the hull that absorbs and fades the energy caused by the impact against the water surface. It is a layer made of regular hexagons of a rigid polymer that encapsulate a light and viscoelastic material which is a rubber specially designed for this system.
When high-speed crafts receive impacts due to the slamming phenomenon, the energy is captured by the viscoelastic layer that is deformed by temporarily storing the energy and protecting the hull. After the impact, the layer viscoelastic gives the stored energy back to the sea. Results show that the damage caused the drastically reduced because the viscoelastic layer protects the inner material.
This protection is not added to the craft structure, it is embedded in the material itself giving as a result more effective and durable protection against impacts. By applying this strategy, we achieve minimizing the damage caused by high-speed navigation and multiplying by three the time needed between repairs of damaged hull.
According to Juan Carlos Suárez Bermejo, the responsible researcher for the team, “by using this new manufacturing technology, the resistance of high-speed crafts are protected even in the hardest conditions of navigation, extending its useful life and improving the safety of the people on board”.
Shipyards, ship owners and ship classification societies have already shown their interest in the gradual introduction of these new developments in the field of shipbuilding.
Reduction of slamming damage in the hull of high-speed crafts manufactured from composite materials using viscoelastic layers Townsend, P; Suarez-Bermejo, JC; Sanz-Horcajo, E; Pinilla-Cea, P. OCEAN ENGINEERING, 159 253-267; 10.1016/j.oceaneng.2018.04.029 JUL 1 2018