Some people have a tendancy to speak in terms of the number on their loos gauge when they should really talk about pounds (like Dan correctly did). There are two versions of the Nacra F18 mast (that's two versions BEFORE the infusion wing mast). The early Nacra Masts (2003 - 2004+) were the 'soft' masts...that's what I have. Sometime in 2004 they went to a stiffer mast with the same profile. On the soft mast, we usually run about 600lbs to 700lbs of tension depending on the wind. I've never been below 600 but then again, my performance in light air has been miserable. I'm not sure what the recommended settings are for the stiffer mast.

NOTE: be sure to check the diameter of the diamond wire and use the proper scale on your loos gauge. Nacra also changed the diameter of their diamond wires mid 2004 and some soft masts received the larger diameter diamond wires.