Mast bend is fine tuned with the Cunningham right? I thought the prebend would only be re-set for a sail change. Watching the racing cats video the sail shape changed a lot as the mast came back the sail got fuller there was a mainsheet trim with every Cunningham adjustment. Have to watch that one again I believe it was a Tornado used in the video they covered rake of the spreaders as well. From my limited experiance on the MK IV every adjustment on the water results in a slowdown before speed increases. I was told by another Boyer owner to set the rake using the trap line as a ruler it should be about the same at the back crossbrace and at the forestays you can adjust for heavy or lite wind only on the beach.