A cost-effective experimental investigation of flow noise with a small-scale buoyancy or ballast-driven model (BDM), aimed at obtaining accurate measurements of total radiated sound power from the model, is presented. Two BDMs, approximately 0.9 m in length, are considered, operating in the DSTG Large Water Tank, which has a length, width and depth of 10 m \(\times \) 10 m \(\times \) 6 m, respectively. The tank functions as a highly reverberant space, and standard room-acoustic methods are used to measure the total radiated power in fractional-octave bands based on the tank reverberation times. The BDMs can reach speeds of order 7 m/s within about 0.7 s, often close to terminal velocity in the case of a buoyant model, before breaching the surface or hitting the bottom. Radiated power estimates are corrected for the reverberant lag associated with non-constant velocity of the model. Radiated noise following the expected sixth power of velocity is observed in the measurements. CFD modelling using the BDM shape, video-based dot-tracking measurements of the BDM motion, and internal accelerometer measurements, are combined to quantify the BDM characteristics such as added mass and drag coefficient, and thus the achievable terminal velocity.