On the Propulsive Performance of a Side-Wall ACV Model over Calm Water (Part 1)
1976 Volume 24 Issue 268 Pages 218-225
Details
1976 Volume 24 Issue 268 Pages 218-225
In order to study the propulsive performance of a side-wall ACV over calm water, towing tank tests were carried out. The purpose of the present investigation is to determine the effects of model weight and side-wall depth on drag, and to consider how the measured drag can be broken down into its components.
Obsevation and measurement of wet area on the inside of the side-walls was made with a fibre-scope apparatus.
The wave making drag and the hydrodynamic drags such as the side-wall frictional drag and water contact drag of skirts are more significant than the aerodynamic drag. Two drag humps are found at Fn=0.6 and Fn=0.38. It is noted that the hump drag at Fn=0.6 is caused by the wave drag, however, the hump drag at Fn=0.38 is caused not by the wave drag but the skirts drag.
An increase in the model weight causes an increase of skirts drag at Fn=0.38 especially.
A significant wetting and scooping action of the rear skirts occurs at Fn=0.38. The nose up moment and the significant water contact drag of skirts should be attributed to this scooping action by the rear skirts.
Above the primary hump speed the drag of the model increases as the side-wall depth is increased. However, at the secondary hump speed (Fn=0.38) these conditions are reversed. The breakdown of measured drag into components shows that the increased drag appearing with the increased side-wall depth is caused by an increase in the frictional darg of the side-wall itself. The reason skirts drag increases at the secondary hump speed for models with shallower side-walls is considered to be that the heave height is reduced because of the leakage of cushion air through the trough of the wave.
