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An all-composite lighthouse at Rava Port

News International-French

25 Apr 2017

The lighthouse is one of the world's tallest all-composite lighthouses. It is made with Divinycell material from Diab.

An all-composite lighthouse at Rava Port
Lighthouses still guide vessels around the many Indian islands. Rava Port boasts a lighthouse sturdy enough to withstand both sea water and cyclones.

Durable lighthouses needed for the Indian coast
With well over 500 islands, India has a need for sturdy and reliable lighthouses. The traditional way of constructing lighthouses is with masonry or concrete, since the Indian climate causes corrosion on steel frame structures. It is both costly and time-consuming, and since the traditional method requires the lighthouses to be made on site, materials, workers and machinery must be transported there, sometimes in difficult terrain. 

Light-weight FRP modules
The problem is solvable with modern materials. Transportable light-weight fiber-reinforced plastic (FRP) modules can be made in factories on the main land and transported and assembled on site. The light weight of the composite materials makes both transportation and assembly smooth and quick. With high resistance to the corrosive seawater and at one-tenth of the weight compared to traditional materials, is also more suitable for earthquake-prone areas.

Vignesh Marine Technical Services 
Recognizing the benefits of FRP, the Department of Lighthouses (DLH) in India initiated a development project to erect a 30 m tall composite lighthouse at Rava Port near Kakinada in South India. Vignesh Marine Technical Services Pvt. Limited (VMTSPL), Chennai, was contracted to carry out the project. VMTSPL in turn engaged Dr. N. G. Nair, from NGN Composites to develop the modular construction scheme, carry out geometric and structural designs and guide the manufacturing process of the world’s tallest hand lay up composite tower. Having worked with Diab since 2010, NGN Composites found Divinycell H60 with OD30 finishing option the most suitable foam for their design.

Hand lay-up modular construction
A hand lay-up modular construction was adopted for the manufacturing of the modules. With a 3.6 m diameter cylindrical shell structure the idea was to create a streamlined air flow around the shell which would reduce wind pressure by 70%. To make molding and transportation more convenient, the maximum length of each module was decided at 5 m. Instead of providing a tapered profile along the length, a uniform diameter profile was chosen in order to be able to reuse the same mold. Five modules of 5 m and two modules with a length of 2.5 m each together made up 30 m height. 

Rigid IPN foam from Diab
The cylindrical shell walls were made of rigid IPN foam from Diab. Flanges were molded both inside, at both ends of the modules, and outside, in order to be able to attach them to the foundation as well as to the flat roof at top. FRP inward flanges were provided for module-to-module bolting from the inside of the lighthouse. This method of bolting eliminated the need to erect scaffolds. A spiral staircase was built of sandwich FRP and landing platforms made of specially-made FRP gratings with FRP skins on top and bottom surfaces were inserted in between the modules. At every landing, the adjacent modules and the landing platform were bolted together. Polyurethane coating was provided to the outer surface to protect from UV radiation damage.

Reliable and safe
For several years, the lighthouse has been lighting up Rava Port without any signs of corrosion or fatigue. Thanks to the structural strength of the core material, the lighthouse has already been exposed to 120 kmph cyclonic wind pressure with no visible deformations.