ADV Measurements of Planing Boat Prop Wash in the Extreme Near Field

Field measurements of the near-bed disturbances induced by planing recreational watercraft are presented. A wide variety of boats and operating conditions were considered. Of particular interest was how the velocity and turbidity at the lake / river bed would vary with water depth, boat speed, and boat power. The results indicate that boats travelling at very low and very high speeds cause very little bottom stirring, even at fairly shallow depths. Boats travelling at transitional speeds, near a depth-based Froude number of unity can cause significant stirring, even in several meters of water. A simple mathematical model of the flow was developed and was found to reproduce the observations reasonably well. Some of the technical challenges of the experiments and limitations of the instrumentation will be discussed.