It enhances steering and maneuverability quite a bit (especially at slow speeds where many single-prop stern drives tend to wander and require constant steering adjustments), assists in getting on plane more quickly, and reduces bowrise. While not always available for smaller, less expensive power packages, having the twin props provides distinct and significant performance advantages. Each have slightly different ratings and applications, but the most significant thing a boat-buyer needs to know is that Bravo Three drives have twin contra-rotating propellers, while the others have a single propeller. All of MerCruiser’s power choices mate up with Alpha One, Bravo One, Bravo Two, or Bravo Three outdrives. MerCruiser has a wide-ranging line-up, to accommodate a number of different sizes and types of pleasure-boats. These diesels are less commonly seen in pleasure boats then their gasoline counterparts, but can be a good choice in certain circumstances. In addition to its gasoline power packages MerCruiser has a line of diesel engines which can be rigged with their stern drives including a 2.0L in-line-four (115, 130, 150, and 170 HP), a 3.0L V-6 (150, 230, and 270 HP), and a TDI 4.2L V-8 (335 and 370 HP). For anything bigger, you'd have to go to Mercury Racing. While they offer some more powerful packages, they’re quite specialized, far more rare, and are intended mostly just for high-performance boats as opposed to your average recreational craft. Finally, MerCruiser has a 8.2L V-8 that generates 380 horses in its regular incarnation, and 430 horsepower in the H.O. Next in the line are a pair of 6.2L V-8s, which put out 300 and 350 horsepower. Today, MerCruiser’s smallest offering is a 4.5L V-6, which comes in 200 and 250 horsepower models. The increase in price due to EPA requirements for a catalytic converter, along with the increasing popularity of outboards on smaller boats, has eliminated much of the market for these diminutive stern drives through the past decade. Although MerCruiser still offers a 3.0L 135 horsepower in-line four package via Mercury Remanufacturing, it no longer offers these smaller block engines with new stern drives. MerCruiser Stern Drives The low-end range of stern drives offered by Mercruiser has shrunk a bit in recent years. This is ideal for watersports, especially wake surfing, where it’s possible to fall into the water very close to the transom of the boat. However, it also moves the propellers forward about 27 inches, so they remain under the boat and away from the transom. This reduces trim range and eliminates the ability to trim the drive up when moored. Forward Drive units face forwards, instead of facing aft. Volvo Penta’s Forward Drive is the biggest technical development of the past decade or more, in the world of stern drives. Thus, the boater gets to enjoy the benefits of inboard power (an automotive-like engine that’s easy to work on and has optimal weight distribution), while also gaining certain advantages of outboard engines (the ability to trim the drive as needed for optimizing performance, the ability to tilt it up for mooring, enhanced handling with the articulating drive, and reduced draft). These two parts join at a hole in the transom of the boat, where a rubberized part called the “boot” seals out the water but flexes to allow the drive unit to move and turn. The engine itself is oriented like an automotive engine, and the rear of the engine mates with a drive unit much like the lower unit of an outboard, which can tilt. A stern drive, sometimes also called an I/O, or Inboard/Outboard, is essentially a combination between inboard engine and an outboard drive unit. What is a Stern Drive? Before we look at each of these big players, let’s make sure everyone’s on the same page and understands exactly what a stern drive is and how it works. MerCruiser and Volvo Penta have a wide range of stern drive offerings, and dominate the American market for this type of marine powerplant.
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