Ocean Thermal Energy Conversion (OTEC) is one of the ocean renewable energies that utilizes the temperature differences in the ocean. Since its power production is very stable, OTEC can configure a redundant and clean power network combining with other natural energy sources. In addition, this energy source would provide an attractive integration with other industries such as an aquaculture with ocean nutrient enhancement, desalination, deep seawater cooling, and hydrogen production. A commercial-scale of OTEC requires a floating plant and an ultra-large Cold Water Pipe (CWP), e.g., 12 m in diameter for a 100 MW plant. Such a CWP is still the most challenging component for floating OTEC. This paper addresses a preliminary design using multiple medium diameter CWPs instead of a single ultra-large CWP. The floating structure is first assumed to be used a pre-owned oil tanker conversion. The multidisciplinary design process takes into account: design trade-off of number of pipes, internal flow velocity and diameter, pressure loss, the risk of contact between the CWPs, structural design, and eventual cost of energy. This preliminary study may be useful in a future feasibility study of floating OTEC.