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Hydrofoil gives Stealth a lift

The Stealth 420 is a South African-built power catamaran that employs

a patented hydrofoil system.

The HYSUCAT hydrofoil was designed by Professor Gunter Hoppe of Cape Town’s Stellenbosch University. Hoppe was approached by the South African Defense Force to develop a way to improve the performance of a catamaran patrol boat, according to builder Stealth Yachts. What he came up with was a hydrofoil that fitted between the patrol boat’s hulls.

“It’s actually been around for some 20 years now,” David Beavis, manager of charter operations for Annapolis, Md.-based Voyage Charters, says of the hydrofoil system. “It’s been used on vessels ranging in size from small rigid inflatables to ferries, and it’s known to work on those vessels.”

The main foil on the Stealth 420 is made of stainless steel and is located amidships, with a pair of bronze stabilizing foils aft. Beavis says Hoppe designed the hull form, as well. “He really designed the hull and foil package to both work together,” he says.

The 420, which Voyage Yachts of Annapolis markets in the United States, has a narrower beam than other catamarans, and the tunnel is designed to create the precise amount of lift, according to Beavis. The hydrofoil also is different.

“Unlike [the V-shaped] hydrofoils that most people are familiar with, that they might have seen on commercial vessels … this foil is very, very much like a delta wing, and it has all the shaping of a wing,” says Beavis. In effect, it creates lift just like an airplane wing.

Draft is reduced to inches when the boat is at speed, Beavis says, and the foils aren’t deeper than the hull bottom. Other advantages of the hydrofoil-assisted cat are improved fuel efficiency, better acceleration, higher top end, reduced motion, longer range, a level ride, and good seakeeping, according to Stealth Yachts. The builder claims 40 percent better fuel efficiency than other boats of similar size, and improvements in speed up to 40 percent at a comparable rpm and engine size.

Unlike some conventional power cat-amarans, the 420 with the HYSUCAT

hydrofoil and hull form banks in turns. In addition, dynamic forces on the foils stabilize the vessel, and the foils dampen wave action, according to the company.

Several versions of the 42-footer are available, including a charter layout and a sportfishing configuration. The so-called “owner’s layout” Stealth 420 has a king-size berth in the master stateroom forward, which is accessed from the port hull and contains a shower and head compartment aft. The starboard hull contains a cabin with a double berth aft, and a washer/dryer and head compartment forward. In the charter layout, there are two cabins in each hull and a pair of smaller head compartments.

On the deck level there is seating in the cockpit, lounge seating and tables in the saloon, a galley forward and to port and a helm station to starboard.

The galley comes with a four-burner stove, stainless steel sink, convection/

microwave oven, refrigerator/freezer, Corian countertops and stainless steel fiddles. A centerline companionway leads up and out through the windshield to the foredeck, which has a sunpad. The flybridge has a helm station with a double helm seat to starboard and wraparound seating. A radar arch is standard.

Four Stealth 420s have been built to date, two of which are in the United States.