Although I have chartered sailing catamarans in BVI numerous times over the years, we are scuba divers and often simply motor from dive site to dive site and then to our anchorage for the evening. We will use the sails a couple of times, usually from North Sound Virgin Gorda to Anegada, and then the return to Jost Van Dyke. The downwind to JVD has always been simple enough, with the mainsail boom extended broadside. This past December we chartered a Lagoon 45 at Dream Yacht Charter on Scrub Island. We had some folks on board that wanted to do some sailing therefore we left Scrub to proceed downwind in the Drake Channel. When we attempted to swing the boom to broadside by releasing the downhaul (corrected to main sheet) the boom then moved not only broadside, but also up in the air. Apparently the only way of moving the boom to either side was to move the short traveler located behind the helm to the side and tighten the downhaul line, which doesn't accomplish much. Is this because this Lagoon does not have a boom vang, or am I doing something wrong?