Fiber-reinforced composites (FRCs) have emerged as transformative alternatives to traditional marine construction materials, owing to their superior corrosion resistance, design flexibility, and strength-to-weight ratio. This review comprehensively examines the current state of FRC technologies in marine deck and underwater applications, with a focus on manufacturing methods, durability challenges, and future innovations. Thermoset polymer composites, particularly those with epoxy and vinyl ester matrices, continue to dominate marine applications due to their mechanical robustness and processing maturity. In contrast, thermoplastic composites such as Polyether Ether Ketone (PEEK) and Polyether Ketone Ketone (PEKK) offer advantages in recyclability and hydrothermal performance but are hindered by higher processing costs. The review evaluates the performance of various fiber types, including glass, carbon, basalt, and aramid, highlighting the trade-offs between cost, mechanical properties, and environmental resistance. Manufacturing processes such as vacuum-assisted resin transfer molding (VARTM) and automated fiber placement (AFP) enable efficient production but face limitations in scalability and in-field repair. Key durability concerns include seawater-induced degradation, moisture absorption, interfacial debonding, galvanic corrosion in FRP–metal hybrids, and biofouling. The paper also explores emerging strategies such as self-healing polymers, nano-enhanced coatings, and hybrid fiber architectures that aim to improve long-term reliability. Finally, it outlines future research directions, including the development of smart composites with embedded structural health monitoring (SHM), bio-based resin systems, and standardized certification protocols to support broader industry adoption. This review aims to guide ongoing research and development efforts toward more sustainable, high-performance marine composite systems.

Metalworking fluid (MWF) supplies a film of lubricant to abate friction, acts as a cooling media to rebate induced heat, and prevents metal pick-ups by flushing away the chips. Hence a liquid used as a cutting fluid reduces wear on the tool, reduces the energy consumption, and produces a better surface quality on the work piece. This paper describes the formulation of a novel water-soluble MWF and its performance evaluation during straight turning and end milling experiments carried out with AISI 304 stainless steel, mild steel, and cast iron as work piece materials. The MWF was prepared by mixing water with white coconut oil as the base oil and food-grade additives as surfactants. Viscosity, pH value, and biodegradability were measured and compared with a commercially available non-vegetable oil–based MWF. The surface roughness and tool surface temperature were measured throughout the machining experiments, and better performances were observed with the coconut oil–based MWF. Tool tip geometry and flank wear for straight turning machining operation were identified by observing scanning electron microscope (SEM) images.

Almost all machining industries in Sri Lanka use mineral oil–based and synthetic oils as metal working fluids during machining. But their usage has potential for long-term environmental pollution and threat to workers’ health. Therefore, much effort has been focused on research and development of eco-friendly and hazard-free alternatives to mineral oil–based metal working fluids, and the use of vegetable oils is one such alternative. This study was focused on investigating the easy access of vegetable oils in Sri Lanka and most commonly machined metals in the local industry, so that the outcome would be much more beneficial to the local industries. After several tests with 10 candidate vegetable oils, white coconut oil is selected as base oil and the results of a successful questionnaire survey directed to select mild steel and AISI 304 steel as the machining metals. Machining experiments were planned using Taguchi methods, and the variation of the surface roughness was tracked with respect to four variable parameters depth of cut, feed rate, spindle speed and metal working fluid. Two mathematical models were developed to predict the surface roughness and optimize the parameters. Further experiments were conducted to investigate the effects of metal working fluid for smooth- and rough-cut conditions. These experiments revealed that white coconut oil is a better metal working fluid for mild steel, while soluble oil favors AISI 304 steel. Different thermal conductivities of metals cause the coconut oil to act differently while machining two metal types.