Tidal stream technology has advanced in the past decade. However, much of this development is still focused on energetic flow and with reason. The cost of tidal stream technology remains to be high and deploying in less energetic currents with Utidal < 20ms results in large values of cost/kW. Nonetheless, deploying in less energetic currents can help the industry tap into new markets and also provide energy to regions that are characterised by less energetic flows such as countries in South East Asia. It is hypothesised that increasing the operation tip speed ratio, and in turn the rotational speed, of turbine rotors can improve the economics of tidal turbines operating in less energetic environments. This is investigated by evaluating six different turbine rotors operating at different rotational speeds. A cost model is adapted to get the relationship of cost to rotational speed. It was found that increasing the speed do reduce the cost of the technology although savings are also hugely reduced after a value near to 50RPM.Finally, the implications of operating at high rotational speed is discussed and the effect of cavitation is quantified through a simple sensitivity analysis and it was determined that going for a NACA blade with optimal tip speed ratio of 7.75 is economically feasible given the model used in this paper.