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.