Join the Cat Crowd
There's no shortage of good reasons to climb aboard a catamaran
Payload vs. Pace: Some designs handle the poundage better than others
With a few exceptions--Prout catamarans came into existence before the age of fiberglass and of singlehanded transatlantic races--cats first entered the public's awareness by sweeping the field in the ocean races in which they were allowed to compete with monohulls. But just as it's a myth that catamarans are inherently unsafe, it's also a myth that they're all fast. They're susceptible to the same performance constraints--poor hull design, too much weight, insufficient sail area, inefficient keels--as monohulls. And as with monohulls, only 10 times more so, every creature comfort you bring exacts its price from speed.
Catamarans are sensitive to loading in direct proportion to their projected performance. "You can add 10 percent to the weight of a monohull and lose maybe one percent of its maximum speed," says Gregor Tarjan, Aeroyacht's president. "Do that to a multihull and you lose 10 percent of speed."
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.
When the boat floats lower, wetted surface grows. If the transoms immerse, drag increases significantly. Perhaps more important than the lost performance, the wingdeck clearance is also reduced. The closer the boat's wingdeck is to the water, the lower the sea state in which it's likely to interact forcibly with waves, a situation that's again uncomfortable and slow.
The tendency of boats to accumulate weight hasn't gone unnoticed by their builders. In several instances, a revised model has simply been lengthened. Two examples are the Dolphin 460, which started life as the Dolphin 430, and the Manta 42, which grew from the Manta 40. Both benefited from their sterns being stretched out. They gained volume aft, some of it below the waterline, supporting the added weight that seems to accumulate back there, around the engine compartments and in the aching voids under cockpit seats and coamings. Extending the existing hull lines farther aft raises the transoms, too, and as long as the bridgedeck remains unchanged, it's now a little more centered on the longer hulls, and the new combination should be less prone to pitching.
Eyeball the transoms and the stems while the boat is afloat and look around the boat to determine its load condition: Are the fuel and water tanks full? Is there a generator? How many anchors and mooring lines? Are provisions and stores aboard? How many people?
If you want to make the most of the boat's sailing potential, pay attention to how much gear you bring aboard. Take inventory regularly, and send ashore anything that hasn't earned its place aboard. Keep those transoms clear of the water.