The stern drive boat was appreciably faster, both at top end and out of the hole, where it also showed less bow rise. In addition, our tests showed that, on average, the stern drive accelerated 20 percent faster from 0 to 30 mph. And it responded more quickly at following sea speeds - where you accelerate to the crest of a wave, then throttle back on its face - of 15 to 25 mph.
The stern drive's fuel efficiency mirrored its speed advantage. At a cruising speed of 24 mph, the stern drive consumed 19 gph, compared to the V-drive's 21 gph, a 10 percent difference. In fact, the stern drive had to be pushed to nearly 32 mph before burning 21 gph. That's a 33 percent increase in speed for a 0 percent increase in fuel consumption.
The faster you go, the greater the stern drive's efficiency. That's because drag increases with the square of speed. And the V-drive is dragging more underwater gear - its shaft, strut, and rudder - than the smaller and more streamlined stern drive. The ability to trim the stern drive means you can set its shaft to line up with the boat's direction. All its thrust is forward. The fixed 12-degree angle of the inboard's prop shafts means a component of forward thrust is lost to upward thrust. Dual-prop stern drives, such as the Bravo Three on our Sea Ray, provide a large efficient blade area within a small diameter. This means you get a lot of thrust with minimal drag. Yes, props cause drag, and it's another reason for the stern drive's efficiency. Overall, the stern drive boat felt more powerful and sporty to run. Although the two boats have an equally tight turning radius, the stern drive boat recovered from hardover turns more smoothly, with less squatting and loss of speed. But don't write off the V-drive, which has a lot going for it as well. It draws slightly less water, and while maneuvering at slow speeds, such as when docking, our V-drive boat handled with more precision and spun more confidently. This is primarily because when you put one engine forward and the other in reverse, the combined turning force is centered closer to the boat's ideal pivot point than with stern drives. It feels as if the boat is standing still and rotating under you, something you don't get with stern drives. Furthermore, boats with engines mounted closer to their center of gravity - as they are in the 310's V-drives - ride better in waves and swells because they pitch less than boats where the engines' weight is farther aft.
Point: Does the V-drive's sea-kindly feel, more comfortable ride, and better slow-speed handling outweigh the speed, efficiency, and extra range of the stern drive? Only you know the answer to this one.
POWER OF THE DOLLAR
F or most boaters, annual maintenance includes engine winterization. A survey of boatyards in various parts of the country confirms that it costs about $350 to winterize a stern drive and about $270 to do a V-drive. Why the difference? There are more parts and thus more labor involved with a stern drive: The drive needs to be removed; the U-joint and gimbal bearing must be inspected and greased; and the bellows gasket and O-rings should be replaced. Of course, annual maintenance doesn't include repairs. For instance, if you kiss the bottom in your V-drive, you may bend a shaft or rudder. Do the same with a stern drive and the lower unit kicks up on impact to minimize the damage. Bend a stern drive's prop - or propset in this case - and you can replace it in the water. But when an inboard prop needs changing, you either have to hire a diver or pay for a haul.
For most of us, the cost of fuel has become a pressing concern. As you can see by the charts on the previous page, the stern drive is more efficient than the V-drive. However, this may not be as damning as it seems. The average boater puts only 50 hours a year on his engines, with 40 percent of that time at idle and one-quarter at a slow cruising speed. Given this, after five years the differences wouldn't be much.
Long term, the stern drive is more tolerant of shaft misalignment should your engine mounts move a bit - and they all do. The longer shaft on a V-drive multiplies any error by the time it gets to the prop. On the other hand, if you run your boat in saltwater, an inboard's stainless-steel and bronze underwater gear can tolerate corrosion much better than a stern drive's aluminum gear.
Point: In the short term, although both boats cost about the same, the cost of ownership is higher for the V-drive boat due to its greater fuel burn. But, in the long term, the stern drive's maintenance issues will make it more costly to live with.
The 310 Sundancer is a first-rate express cruiser, worthy of topping anyone's list, particularly because it offers you that rare choice: stern drive or V-drive. So which drive train do we think is better suited to this boat? Depending on where and how you go boating, a case can be made for each. But given that most boaters will use an express cruiser for day trips and overnights on calm freshwater, and the serviceability and efficiency afforded by the stern drive, we think that for most skippers the I/O is the way to go.