I'm assuming you're asking if a H18 mast can be stepped without mechanical assistance? It is possible if you're fairly tall and have a bit of strength but it is a very heavy mast. I used to step my H16 mast by myself with hardly any effort at all. The 18 mast is another story. Mast stepping devices are available (page 35 of the 2006 Hobiecat catalog or page 54 of the 2006 Murrays catalog). All of them require that you have a trailer winch. Here's how I do mine (without one of the stepping devices);
1) After all of the obvious preparations have been made, bring two of the trapeze lines (one from each side) forward and hook the trailer winch line to the trapeze handles.
2) With another person ready at the winch (assuming you have one), stand on the aft crossbar and lift the mast enough to where the person at the winch can begin winching the mast up (make sure you leave the front tie-down straps on the hulls until the mast is raised).
3) The winch is now handling all of the weight of the mast. Your job is to walk the mast up keeping it from falling to one side or the other. The higher it gets, the less chance of it falling off to the side as the side shrouds take over.
4) Once the mast is up, pin the forestay into the bridle wire. By the way, this is how I tighten my rig, by cranking down on the winch as it's attached to the trapeze wires until I get it nice and tight and then attaching the forestay. You must keep the aft hull tie-downs on also if you're going to do this as it will tend to lift the back of the hulls up.
Hope this helps,