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Hull Bottom Technology

Take a look at the latest designs that help improve stability, efficiency, ride, and handling.

As long as there have been boats plying the water, there have been boatbuilders trying to find more efficient, better-riding hull bottoms. Those we're showing here are some of the latest tweaks and improvements we've seen in the never-ending quest for a better hull. Our editors have had firsthand experience testing boats with all of these designs in various sea conditions, and have found that each type has its own advantages and disadvantages.

Step It Up

Stepped hulls work on the principal of reducing wetted surface, which in turn reduces friction between the hull and the water. A step in the hull is an abrupt change in hull-height running athwartships, from chine to chine, and ending with a notch in each of the hullsides. As the boat begins to plane, an area of low pressure is created immediately aft of this transition, drawing in air via the notches.

Hull design multi-step profile view

Hull design multi-step bottom view

Steps in one form or another have been around for more than a century, but it's quite difficult to create a step that results in both efficiency increases and good handling. Often with poorly designed steps, the introduction of air under the hull has the unfortunate side effect of reducing stability while on plane, because some sections of the hull are no longer supported by the water.

In the past couple of decades with the help of modern CAD design, however, many builders have overcome this issue. More recently, they have managed to take the concept one step further — literally — by introducing multistep designs that boost speed and efficiency to the tune of 10 to 15 percent. Two good examples can be found in SeaVee's Z-series boats and in many Formula models. Today, the main downside to multiple-stepped hulls is the increased cost associated with R&D and increased design complexity.

Riding On Air

Another way to increase efficiency while also improving ride is to utilize a hull design that compresses air under the hull. This can provide additional lift while also creating an air cushion of sorts under parts of the boat, which reduces wave impact. The most common example is a powercat that has a "compression tunnel," which is widest at the bow and grows slightly narrower as you move aft. The biggest downsides to utilizing this design are the potential for a sharp "snap" roll (which can occur when beam seas cause one hull to drop into the trough while the other rises on a wave); misting out of the front of the tunnel, commonly called "sneezing," and tunnel slap (when both hulls submerge all the way and the top of the tunnel slams against a wave). In recent years, however, there have been several modifications to basic powercat designs, in some cases combining them, more or less, with a V-hull.

Hull design Mako bow view

Hull design Mako stern view

The Mako "Inverted V" hull, used on its line of small inshore boats called Pro Skiffs, is one example. We've found these boats do compress some air centered under the hull and, as a result, they run significantly smoother than more common semi-V hulls usually found on boats of the same size. They don't suffer from a snap roll or sneezing. The handling takes a bit of getting used to, however, because the boat doesn't bank in turns in the same way as a V-hull.

Hull design Bayliner bow view

Hull design Bayliner stern view

Bayliner's M-Hull design, found on its Element line, tilts more toward a traditional hull in the center but incorporates small V-shaped protrusions to either side, which pack some air while also enhancing stability. We've found that these hulls do in fact feature unparalleled stability, and they run slightly more smoothly than most boats of a similar size. That said, they can be less sensitive to trim and usually maintain a more or less flat attitude while running. The propeller can tend to ventilate when boats with this hull design are put into hard turns, especially if the engine is trimmed up at all.

Breathe In

Steps and compression tunnels aren't the only way to get air under a boat's hull to reduce friction. Beneteau takes a completely unique approach with its Air Step system, used on many larger models (up to 46 feet), which actually pipes in the air. Vents located above the waterline run through the boat and to its hull bottom, introducing a flow of air to reduce friction between the hull and the water.

Hull design power cat bow view

Hull design powercat stern view

Bayliner's M-Hull design, found on its Element line, tilts more toward a traditional hull in the center but incorporates small V-shaped protrusions to either side, which pack some air while also enhancing stability. We've found that these hulls do in fact feature unparalleled stability, and they run slightly more smoothly than most boats of a similar size. That said, they can be less sensitive to trim and usually maintain a more or less flat attitude while running. The propeller can tend to ventilate when boats with this hull design are put into hard turns, especially if the engine is trimmed up at all.

Breathe In

Steps and compression tunnels aren't the only way to get air under a boat's hull to reduce friction. Beneteau takes a completely unique approach with its Air Step system, used on many larger models (up to 46 feet), which actually pipes in the air. Vents located above the waterline run through the boat and to its hull bottom, introducing a flow of air to reduce friction between the hull and the water.

Hull design Aspen stern view

Hull design Aspen top view

Aspen says the smaller hull has a 50-percent reduction in drag due to width, plus another 20-percent reduction thanks to the absence of running gear. As a result, its 40-foot model can attain almost 9 mpg at speeds of 6 mph and more than 2 mpg at speeds approaching 20 mph. As a point of reference, many modern trawlers of similar size get 3 or 4 mpg at 6 mph and less than 1 mpg at planing speeds.

Illustrations by ©2018 Mirto Art Studio

Author

Lenny Rudow

New Boats, Fishing & Electronics Editor, BoatUS Magazine

Top tech writer and accomplished sports fisherman, BoatUS Magazine Contributing Editor Lenny Rudow has written seven practical boating books, won 30 awards from Boating Writers International — many for his marine electronics articles – and two for excellence from the Outdoor Writers Association of America. He judges the NMMA Innovation Awards, and is Angler in Chief at FishTalk, his own Chesapeake-based publication. A great teacher and inspirational writer, Lenny hosts many of BoatUS Magazine’s very-popular how-to videos, which can be found on the BoatUS YouTube channel, or at BoatUS.com