Think about the excruciating forces placed on the lower unit of today’s big, powerful outboards. There’s torturous twisting force as horsepower is transferred down a drive shaft to a set of gears, then bent 90 degrees to spin a propeller. There’s also the brutal impact of water at high speed.
And then there’s “down force” or what some call “shoulder weight.”
“When on plane, the weight of the boat rests aft, much of it riding on the propeller, torpedo and anti-ventilation plate,” said Steve Miller, brand manager for large outboards at Mercury Marine. “So the gear case has to be built to carry such weights, which are getting greater all the time.” Miller points to the trend of outboard-powered boats up to 40 feet in length and 13 feet in beam, most with triple or quadruple outboards.
Simply put, today’s big outboards need bigger shoulders. This was the thought behind making the 5.44-inch gear case standard on Mercury 225 hp through 300 hp Verado outboards. The 5.44-inch replaces the original 4.8-inch gear case on all but six of the 26 current Verado iterations.
“The original gear case is still good, particularly on lighter, high-performance craft such as bass boats and flats boats,” Miller said. “But bigger boats need bigger gear cases.”
First appearing on the 350 SCi Verado from Mercury Racing, the 5.44-inch is beefier in a number of ways. As the name implies, the torpedo is 5.44 inches in diameter vs. 4.8 inches for the original. The torpedo and skeg are also longer, and the anti-ventilation plate is substantially wider and elongated to improve planing time and stability at speed with heavier hulls.
Inside, the pinion gear is 24 percent larger, and the drive gears are 14 percent larger. The clutch dog is 30 percent longer and has five times the impact resistance of the dog in the 4.8-inch gear case, Miller said.
The lower end of the drive shaft is stronger, thanks to greater girth and a high-capacity needle bearing for added pinion gear support. The drive shaft is also designed to lift gear oil to the upper bearing.
The gear lube fill and vent plugs are located in the bearing carrier (which is 17 percent larger), so to change the lube, you remove the prop. The 5.44-inch gear case weighs 13 pounds more than the original.
Because the 5.44-inch gear case is less hydrodynamic, boaters might expect a performance decrease. “Up to 60 mph, any decrease will be negligible,” Miller said. “But you will experience better handling at cruising speeds due to the increased lift.”
There are two versions of the new gear case: the black 5.44-inch with a 1.85:1 gear ratio (same as the original) and the silver 5.44-inch HD with a 1.75:1 gear ratio, which is designed for heavy-duty commercial and government use. With a 1.25-inch prop shaft, the silver 5.44-inch HD requires Mercury Racing’s Flo-Torq II HD solid hub system, while the black 5.44-inch has a 1-inch prop shaft and uses Merc’s breakaway Flo-Torq II hub system. The 350 SCi will be equipped with the 5.44-inch HD going forward.
According to Merc, the new gear case carries no upcharge. For example, the Verado 225L with the 4.8-inch gear case has a manufacturer’s suggested retail price of $19,860 — same as the 225L with the 5.44-inch gear case. Verados currently in service can be retrofitted with the new gear case, but Mercury was mum on the cost of the gear case alone. Said Merc, that’s a question for your dealer to shoulder.
