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.
The problem is easily solvable with modern materials. Transportable lightweight fibre-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.
Recognising the benefits of FRP, the Department of Lighthouses (DLH) in India initiated a development project to erect a 30m 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 layup composite tower. Having worked with Diab since 2010, NGN Composites found Divinycell H60 with OD30 finishing option the most suitable foam for their design.
A hand lay-up modular construction was adopted for the manufacturing of the modules. With a 3.6m 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 moulding and transportation more convenient, the maximum length of each module was decided at 5m. Instead of providing a tapered profile along the length, a uniform diameter profile was chosen in order to be able to reuse the same mould. Five modules of 5m and two modules with a length of 2.5m each together made up 30m height.
The cylindrical shell walls were made of rigid IPN foam from Diab. Flanges were moulded 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.
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 120kmph cyclonic wind pressure with no visible deformations.
