Hi together, please find attached a parametric model of a costa bulb and a feature definition. To recover the energy which gets lost by the hub vortex of the rotating propeller a costa bulb can help. I integrated the rudder bulb setup into the feature "Spade Rudder" which is shipped with CAESES/FFW. The bare hull to which I attached the appendages is also shipped with CAESES/FFW. All you need as input are some propeller parameters. Please find the feature here: baseline > abdy > appendages > feature:rudder Cheers Matthias (fdb file edited, 30.09.2014) containerVesselCosta.fdb