This analysis used the Flow Simulation module in SW 2011 ( Not Flow Xpress). This module lets you look how air/water behaves around an object - or in this case - an attachment to the shell. Particularly for water, you can firstly create the water flow around the the hull, giving you the boundary layers, hull drag & wave drag ( if applicable) and then run various fin designs in a more realistic body of water. This fin actually did not do so well in testing! It was fin at a constant velocity but when pitching, rolling and acceleration were introduced, the transiant flow ( conversion from laminar to turbulent) reduced significantly and the 'drag: torque' ratio became to high.