The narrow hulls of a fast boat will immerse more quickly than the wider hulls of a more cruiserly craft. And because cats have so much volume and deck space, it's easy to load them up. An average 40-foot cruising cat with a hull-to-beam ratio of 8:1 has a pounds-per-inch- immersion measurement of about 1,300 pounds. One hundred gallons each of diesel (700 pounds) and water (800 pounds) will set it down an inch. A 50-pound anchor with 250 feet of 3/8-inch chain adds 450 pounds, and you'll probably want three anchors, a couple of spare rope rodes, and half a dozen mooring warps, bringing you close to the second inch. Add a generator in its sound shield, an air-conditioning compressor, and a foursome of air handlers, plus a battery charger and an inverter, and you're looking at your third inch. It's not unusual on a 40-foot cat to see a 12-foot RIB with a 20-horsepower outboard, a rig that can easily weigh 500 pounds, slung from davits that weigh another 100 pounds. Add to that a barbecue, diving gear, a kayak, and a windsurfer, and you're well on your way to your fourth inch. We haven't yet added tools and spares, never mind food, beverages, pots and pans, linens, or even people. If you attain the advertised capacity payload, which for a 40-foot cat might be about three tons, the boat will float almost five inches below its designed "light ship" waterline.