Reducing bubble sweepdown effects on research vessels

During early stage hull form design trade studies are performed to investigate feasible and desirable attributes for the a oceanographic ship. Paramount among these attributes is excellent sonar mapping capability. This paper summarizes some of the design and analysis effort to improve sonar capability by minimizing bubble sweepdown interference while considering overall ship resistance and fuel economy. Bubble sweepdown and its detrimental effects on scientific sonar systems is a widely known phenomenon that has been experienced to some degree on nearly every research vessel. The causes and mitigation techniques are less well understood. Sonar performance is degraded when bubbles pass over or near transducers. These detrimental effects are usually worse at higher ship speeds and sea states. Gondolas, fairings and bubble fences can effectively reduce bubble sweepdown interference but generally incur significant resistance penalties. In this study, several hull form bow shapes and sonar mounts were investigated. Computational fluid dynamic (CFD) analysis was conducted to determine their effect on bubble sweepdown near the transducers. Tradeoffs between sonar performance, draft and resistance are explored. The impact on ship specification development is also reviewed.