The line spectrum characteristics of the radiated waterborne noises of an underwater vehicle can be reconstructed using the technique of chaotification, which can improve the acoustic stealth of the underwater vehicle. According to the particular application background, in this paper we study the chaotification issue with nonlinear time-delay feedback control for a double-layer vibration isolation floating raft system under multi-source excitation. From a simplified two-dimensional floating raft system model, a chaotification method with nonlinear time-delay feedback control is presented completely. It provides a standard procedure for line spectrum chaotification design. Numerical simulation results show the feasibility of this method. Under multi-source excitation, the effects of the control gain, time-delay and feedback frequency parameters on chaotification are investigated, and discussion is also extended to the case of the single-source excitation.