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Boats

It’s All About Performance

It’s All About Performance

Surface-drive systems are allowing high-speed-boating enthusiasts to fly, literally, across the water.

By Capt. Patrick Sciacca — June 2004

   


 More of this Feature

• Part 1: Surface Drives
• Part 2: Surface Drives
• Piercing Props


 Related Resources
• Feature Index

 Elsewhere on the Web
• Arneson Industries
• Seafury Propulsion

The trawler crowd may not be into speed, but most other boat owners like to occasionally open up their engines and skip across the water like a flyingfish. I know I do. There’s a certain machismo about speed, and I enjoy it in short bursts. On a good day, my 31-footer hits 40 mph. The speed doesn’t last long, though, as the fuel consumption races equally fast from 25 gph to 60 gph.

While many of us enjoy brief interludes of high-speed boating, there are adrenalin aficionados who dig big speed (try 60-, 70-, and even 150-plus mph) all the time. Instead of using house-size powerplants that burn fuel like lemmings eat grass, many performance enthusiasts are running faster and more efficiently with surface drive technology. And, thanks to the surface-drive’s trademark rooster tail, with more flair, too.

At first glance, a surface-drive system doesn’t look like any propulsion technology you’ve seen. It has a short shaft off the transom and most closely resembles a stern drive. But unlike the stern drive, it doesn’t hang down, the shaft shoots straight back. In fact, when a boat is underway, almost the entire drive unit is out of the water. In addition, the propeller on a surface-drive unit is different (see “Piercing Props,” this story). It has to be designed—unlike a completely submerged straight-inboard or stern-drive system—to work in both air and water. When running at high speed, only about 40 to 50 percent of a surface prop is in the water.

There are two types of surface drives, fixed and articulated. The fixed system utilizes rudders and works great for straightaways, but it also reduces maneuverability and it cannot be trimmed, so the boat’s running attitude is constant. The articulated system, developed by Howard Arneson and known as the Arneson Surface Drive (ASD), allows the driver to change the amount of prop in or out of the water, thus affecting the boat’s attitude. The ASD’s articulated joint also allows the propeller to be directed and provide better steerage than a fixed system. This is not the only way to steer with surface drives; other methods include utilizing a rudder aft of the propeller that’s cantilevered off the surface-drive support structure, or a transom-mounted rudder ahead and “transversely offset” to the side of the propeller. In an article from Professional Boatbuilder, naval architect Paul Kamen says that the articulated drive offers the same effect as being able to change the diameter of a fully submerged prop.

To optimize a surface drive’s ability, your boat should be built from the get-go to accommodate this technology. For instance, a squared-transom boat could deflect water when in reverse and reduce effective slow-speed handling. It could even give the effect of forward thrust, according to New Zealand-based surface-drive manufacturer Seafury Propulsion. Magnum Marine, one of several performance-oriented boatbuilders (some others include Pershing and Baia) that use surface-drive systems, says its boats have drives installed on a vertical transom surface, which enables the drives and thrust to work as a hull extension. Magnum’s president, Katrin Theodoli, says that her company puts a small wedge between the transom and the drive plate so the drive is square. The result provides uninterrupted water flow through the drive, optimizing the performance of Magnum Marine’s boats.

Next page > Part 2: Like any propulsion system, there are cons, too. > Page 1, 2, 3

This article originally appeared in the May 2004 issue of Power & Motoryacht magazine.

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