Stepped bottoms have added many benefits to a boat's performance, mostly increased speed and fuel economy. But rarely have you heard that they benefit a boat's handling. Why? Steps force air beneath the boat's hull, which can disrupt the hull's adhesion to the water. Less adhesion equals less maneuverability.
Or so they say. While developing its new 38 ZR for a return to offshore racing, Donzi consulted Jim Caldwell, who was instrumental in designing the first stepped hulls for Fountain. Donzi claims that Caldwell's new design, called Fluid Diversion, improves a stepped-hull boat's handling by diverting water away from certain sections, or pressure points, on its running surface. As you initiate a turn, water is pushed away from the bottom of the inboard side of the hull, resulting in more stability.
The 38 ZR's two steps are approximately 1" tall and run aft from the chine to the keel. The deadrise varies in each of the boat's three running surfaces-ahead of the front step, between the steps, and abaft the second step-to aid in water diversion. The majority of the displacement is on the third running surface. At 85 mph, 14 square inches of the forward bottom section contact the water. Amidships, the area grows to about 33 square inches, and in the aft bottom, the contact area is 60 square inches. For lateral stability, the 38 ZR's bottom has a V-pad about 1'3" wide with varying side heights depending on the location in the bottom.
The Highs: Lower profile and low center of gravity give the driver a better feel for the boat. F-16 canopies, bucket seats, and a power footrest provide exceptional comfort. Aft deck boxes provide needed stowage capacity.
The Lows: All that engine hatch space and no upholstery for bikini-clad babes to lay on. Needs gas struts on locker hatches abaft bench seat. Too pricey for stock 500s. No portable head.
Does it work? During my test, I made rapid-fire slalom passes at 40, 50, and 60 mph. Quick directional changes often upend a stepped hull, but the 38 ZR tracked through cleanly and never bobbled. At 70 mph, I mimicked a three-buoy turn that you would take in an offshore race and the boat held its line perfectly. As I completed the maneuver, I hit the gas and imagined myself heading for the checkered flag.
What few waves I encountered were dismissed without so much as a flinch and when we cranked up the 470-hp Mercury Racing HP500EFI Bravo XZs, we hit 85.8 mph at 5200 rpm. In subsequent runs at Mercury's Lake X test facility, after some drive-height adjustments, Donzi said it kicked up the top speed to 88 mph.