Many areas of seas, harbours and channels that were considered deep and safe for vessel navigation have been changed into dangerous shallow water regions for the new generation vessels due to their drastic increase in size and speed. Hence, the understanding of the safe speed of a vessel to prevent it from grounding when it operates in restricted waterways is gaining more importance. A catamaran vessel, being one of the new generation vessel configurations, is considered here to study the effect of its under-keel clearance of water and also its demi-hull spacing in the determination of a safe vessel speed. The numerical study using RANSE based CFD solver Fluent has been complemented by results obtained from experiments carried out in the towing tank of IIT Madras using the newly commissioned floating false bottom facility. © 2010 - IOS Press and the authors. All rights reserved.