Hi
On the upper Nile Fellucas (mentioned by malcolmfry) are the standard river traffic (both used by the locals and used to give tourist trips). For normal short tacks, they didn't bother to change the sail, boom etc. to the other side of the mast. However with some of the larger ferries (back and forth across the river) when they stopped at the bank, the sail, boom etc. was hauled vertical, in line with the mast, while unloading/loading, and when lowered again, it was on the downwind side of the mast for that trip. The tourist Fellucas were tied up waiting, with the boom, sail and yard (if thats the correct term for the big pole on top of the sail) all hoisted up vertical in line with the mast, when lowering, bottom end of the yard was attached to a chain that was fixed to the hull, allowing some side to side movement while not allowing it to lift.