The renewable energy in the Philippines has a very low share in the country’s power generation. It is then determined that the total potential of tidal in-stream energy in the Philippines is more than 80GW, which is more than enough to supply the 75GW target ORE capacity by 2025. However, the tidal flow around the country averages only at about 0.40-0.80m/s. This inhibits the development of tidal turbine technology since TSTs are currently very expensive and the low velocity flow will translate to very low energy captured per turbine. Thus, a preliminary blade design that is optimized for low velocity flow is implemented using computer simulations. Low velocity flow allows for the usage of high-tip speed ratio blades since cavitation is not a big issue; the linear speed of the blade is low even if the blade is operating at a high tip speed ratio. The NACA 63-8xx series blades are able to have maximum Cp values at higher tip speed ratios (TSR > 5.5). The study investigates the blades as they are made more slender to enable maximum output at even higher tip speed ratios (TSR = 7). The most slender blade is found to have a lower power output relative to the base case although the decrease is only at 3%. Thrust loads are also lower, however, the smaller cross-sectional area results in higher stresses. Nonetheless, static load simulation shows that the stresses are well below the allowable yield stress of a typical GFRP blade. This means that the slender blade may be considered in a low speed tidal flow condition and minimisation of cost due to lower loads and lower torque requirements for generators.