Of more real-world importance on a boat like the 290 Amberjack is fuel consumption. At wide open throttle it was about the same for all three boats. But when comparing fuel consumption at the same speeds, the stern drives again had a decided advantage. The stern drive ran 34.7 mph at 3500 rpm, pretty much the same as the 260-hp V-drive's 34.5-mph top speed. In terms of fuel consumption, the stern drives burned only 22.8 gph at 3500 rpm versus the V-drive's 40 gph at WOT. At 4000 rpm the stern drive boat hit 39.4 mph and consumed 25.2 gph-about 1 mph faster than the 300-hp V-drive's top end, which ate 40.6 gph at the same rpm. Those numbers equal big advantages in speed and economy. And the advantage goes to the stern drive.
CERTIFIED TEST RESULTS: 260-hp Stern Drive. Advertised fuel capacity 230 gallons. Range based on 90 percent of that figure. Performance measured with two persons aboard, half fuel, no water. Sound levels measured at helm, in dB-A.
TEST POWER: Twin 260-hp MerCruiser 5.7L EFI Bravo Three V-8 gasoline stern drives with 350 cid, 4.00" bore x 3.48" stroke, swinging 15 3/4" x 22" and 14 1/4" x 22" three-bladed ss props through 2:1 reductions.
PRICE: $125,347 During our planing tests, however, the 300-hp 350 MAG MPI Horizon V-drives came through-the boat planed in 5 seconds flat whether we used trim tabs or not. The 260-hp stern drives got the boat on plane in 6 seconds with the tabs down and in 6.5 seconds with them up. Not far behind were the 260-hp V-drives, which took 6.8 seconds tabs down, and 7.2 tabs up. The added grunt of the 300-hp V-drives helped make up for the stern drive's ability to match its trim to the boat's speed. From 3500 rpm to top end, the 300-hp V-drive boat ran at the same angle as the stern drive boat when trimmed for optimum efficiency. By comparison, the 260-hp V-drive boat rode with a more bow-high attitude.
WHAT A DRAG
So there we were with these unexpected numbers. The V-drives had the same or more horsepower, sported larger props, and should have been less affected by a loss of power from internal gearing. The 260-hp 5.7L V-drive is lighter than the 5.7L stern drive, 880 pounds versus 994. What happened? Why were the V-drive boats slower and less fuel efficient?
LOA.....29'0" Beam.....10'6" Draft.....2'10" Displacement (lbs., approx) ........11,300 Transom deadrise...21° Bridge clearance...7'2" Minimum cockpit depth.......2'1" Max. cabin headroom..6'4" Fuel capacity (gal.)...230 Water capacity (gal.)...........30 Price (w/standard power) ........$118,430 STANDARD POWER: Twin 240-hp MerCruiser 5.0L Bravo Two V-8 gasoline stern drives.
In a word: Drag. V-drive boats are inboards, which means they have two shafts, two struts, two props, and two rudders beneath the boat, all creating more drag than an I/O's sleek lower unit. Although the ZF 63-IV drives produce a relatively shallow 12-degree shaft angle, they can't be as efficient as a stern drive, which has no fixed shaft angle and can direct all of its thrust in the desired direction - forward. At high speeds, stern drives can be trimmed up. This lifts the bow slightly, taking some of the boat out of the water, which further reduces drag.
Not only did the V-drive's submerged hardware slow us down, it made things noisier in the cockpit. The stern drive boat peaked at 86 dB-A; the 260-hp V-drive at 90 dB-A; and the 300-hp V-drive at 94 dB-A. It should be noted that the 300-hp boat didn't have the sound-deadening cockpit carpet in place; the other two boats did. We could feel the water coming off the V-drive's props. As the water hit the hull, it caused a slight vibration beneath our feet.
Handling for each was also different. At cruising speeds the stern drive could carve a tighter turn, easily making a 180 within the confines of a 1/8-mile-wide river. The only way to make the same turn with a V-drive was by lowering the outboard trim tab to lay the boat more on its side, letting the strakes and chines get a better bite.
In slow-speed maneuvers, such as docking, the V-drive holds an edge because the props are farther apart by 2". This may not sound like much, but the difference is obvious to anyone pivoting in a wind. V-drives also have more torque to help push the boat around using short bursts of throttle.
The 290 Amberjack has three strakes per side, 4"-wide chines that are turned down slightly, and 21 degrees of deadrise at the transom. The only difference in the bottoms among our three competitors was that the V-drive models had two recessed prop pockets. There's also some downward "hook" incorporated into the bottom aft of the props that helped keep the bow down and the ride level. Also, since Sea Ray assumes the V-drives will be used in salt water, V-drive boats leave the plant with bottom paint, which cuts about 1 mph from the top-end speed.
The engines in a V-drive configuration are installed facing aft with the tail end of the motors and the transmissions accessible directly under the hatch. One of the biggest space eaters in this installation is the 4"-diameter mufflers that exit through the bottom of the boat and relief ports out the topsides. They block access to the batteries and other accessories mounted outboard of the motors, while the same areas are wide open on the stern drive boats. To Sea Ray's credit, the sea strainers for the V-drive engines are easy to get to on the engine compartment bulkhead.
The stern drive's motors are closer to the stern, leaving plenty of space between the front of the motors and the engine compartment bulkhead, compared to the tight squeeze on the V-drive installation. This makes maintenance easier, as does the fact that the drives themselves are mounted externally and easy to get at. But, then again, those same drives will likely need more servicing.