the prebend applied to the main beam means that the downward mast loads only deflect the main beam back to a normal flat condition...i.e. where it is neutrally loaded vertically. Because the system is then shorter than this condition, the dolphin striker is placed under a great deal of tension which translates to compression on the main beam.

Even without the pretension of the main beam and the fixed (bolted) system, any deflection the main beam experiences from the vertical mast loading is immediately translated and magnified (10 fold or better) into tension on the dolphin striker...i.e. 10mm of downward deflection of the main beam would mean the dolphin striker would have to stretch 50mm each side!...Even though it's bolted together, for all practical purposes, the upward force or downward deflection force experienced by the main beam is minuscule (and negligible) compared to the compression it's experiencing from the striker. It's truss engineering.