Correct, I just looked up in my copy of 'Sailing for Dummies'. Not a 'downhaul' as I stated, but the 'main sheet' attached to the short traveler behind the helm. Previous catamarans I have chartered had what appeared to be a 'fixed' boom vang, whereas this Lagoon 45 had no boom vang at all, neither fixed nor adjustable. I guess this was the issue …. nothing to control the tension of the sail's leech? It seems this would prohibit the use of the main sail in a downwind run, and limit the use of the main sail to a broad reach or worse?

https://www.boataround.com/us/boat/lagoon-450-f-fin-tonic