Owners of midsized cruisers craving a stock stern drive now have a heavy-duty option: the Konrad 560 Twin Prop. Like all Konrad Marine products, it's rated for serious use and hand assembled to blueprint specifications. And I know this first-hand because I built one of Konrad's stern drives for a feature story ("Drive School," January).
The 560 Twin Prop expands Konrad's product line. Its 520 single-prop drive was good for boats up to 5,000 pounds, and its 540 was designed for boats up to 7,000 pounds. The new 560 Twin Prop is targeted for boats as heavy as 11,000 pounds and was tested on a single-engine Zodiac rigid hull inflatable that weighed 8,500 pounds.
If you have any doubts about a Konrad drive's ability to handle rough conditions, forget them. The company built its reputation making tough drives for military applications that endure countless hours of abuse and rarely come back to the factory. Konrad constructs all of its drives to blueprint specifications, which have much tighter tolerances than the manufacturing specs that other builders use.
The 560 Twin Prop could be used as a direct re-placement in a single or twin installation or even as part of a repower in which one large engine would replace two small ones. Whether it's used with a diesel or gas engine, the 560 Twin Prop is rated for a maximum torque input of 738 ft-lb and a gross weight-to-horsepower ratio of less than 20 pounds/hp. It's available in a range of gear ratios from 1.21:1 to 1.67:1 and takes counter-rotating propellers up to 15" (front) and 15¼" (rear).
Taking a closer look at the drive's makeup, the 560 Twin Prop has the same upper section as the other units in the 500 series, but the lower unit is a new fabrication. Tapered roller bearings are spaced for optimum load carrying abilities to support the heat-treated steel shafts. Gears are also formed from heat-treated alloy steel, which provides maximum strength. The universal joint is the biggest in the industry for longer life. A housing cast from heat-treated aluminum is finished with a multistep corrosion-resistant finish. A trim pump is included in the standard equipment list.
You need to add your own reversing transmission between the drive and engine. Plus, the drive doesn't discharge exhaust, nor does it have a water pickup. Exhaust would exit through the transom and a remote pickup for cooling water would be required. Propellers, a heavy-duty upper housing, steering system, and other parts are available as options.
The 560 retails for $14,995, which is about $1,000 higher than Konrad's single-prop offerings. Contact: www.konradmarine.com