# Can a “surface drive” propeller be submerged if induced supercavitation reduces water surface area?

Assuming induced supercavitation (like Supercavitating torpedo and Juliet Marine Systems Ghost) reduces water surface area does that reduce friction enough to submerge a surface drive propeller without a reduction in thrust if the reduction in surface area equals what would be on the surface?

As far as propeller design goes, the devil is in the details. You have to account for static pressure (depth pressure). You have to account for the effective speed of sound in the different bubbly regions (the speed of sound in mixed phase flows can get stupid slow, so you end up with supersonic blade speeds and normal ogival blades don't work.) And you have to recognize that normal flow models just don't work. In order for bubbly flow models to work, you need to operate on a scale where for some representative length $$\epsilon$$, the flow properties change very little over this distance, but the distance is still very big compared to the bubble or cavity sizes. This condition simply isn't met in ventilated propellers.