Go to Norg, notice when the ship THERE is getting ready to leave in any "evening" time slot. HP warp to Selbina, jump on boat to Mhuara, you got pirates. Works every time for me every week I've done this without fail. Worst part is waiting a bit in Norg, which can be problematic with coinciding the ride.... but now guesswork is nearly over.
Now to get one where you have to ride the airship to Kazham. Or ride a chocobo from a city to Jeuno. There's some ideas...