To investigate the relation between manoeuvering tests using a free running ship model and ones using a forced oscillator, the authors, at first, carried out the fundamental experiments : sinusoidal steering tests (ω' =0.042.2) and forced oscillation tests (ω' =0.040.15, h ₀/ L_pp = 0.174.7, L_pp =1.3m). Utilizing these results, they discuss convenient forced ocillation tests, which are not only available as the above forced oscillation tests, but also effective to study how to simulate free running conditions. Practically, according as the external force and moment delivered to the ship by the apparatus became small, the ship conditions on the convenient test became similar to those of the free running model. And finally, when the external force and moment were negligible small, a well agreement between both conditions was recognized.