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Roger's antagonism with Conrad III of Germany prior to the crusade and his forces outright naval raids against the Byzantines during the 2nd Crusade had major effects on the crusaders' march routes and the amount of Byzantine military/logistics aid available to the crusaders.
As ASB as it might be to change Roger's mind/personality, what if before the crusaders set out in 1147 Roger set aside his differences with Conrad and made (and kept) a holy pledge not to interfere with Byzantium while the crusade lasted?