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Drive Train Boogie

Stern Drive VS. V-Drive: Which is right for you?

February 22, 2007
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Stern drives are the overwhelming choice of propulsion for owners of small express cruisers; yet there exists a small group of boaters who prefer inboards. Is there a hard-and-fast rule as to which one is better? To find out we headed to the world headquarters of Sea Ray Boats in Knoxville, Tennessee. There, tied to the several hundred feet of company dock jutting into the French Broad River, was an identical pair of 310 Sundancers with the same power, equipment, fuel, and water that Sea Ray had provided. They were identical in every way except one: the drive train. Although both boats hid twin 300-hp MerCruiser 350 MAG MPI Horizon V-8 gasoline engines beneath their hatches, one turned its props through Bravo Three stern drives while the other used V-drive gears and shafts. We ran them, maneuvered them, and crawled through each boat’s innards inspecting every limber hole, motor mount, and tiewrap. We found the distinct differences propulsion choices make possible. Now, all you have to do is figure out which one works better for you. Here’s what you need to know. The 310 Sundancer is one of the most popular express cruisers. It provides sleek styling and crisp decor with expansive exterior seating and the ability to sleep six. I particularly like the foldaway transom bench that provides aft-facing seating, a covered sink and stove in the galley that help gain more counter space, and a cockpit wetbar large enough to accommodate an optional barbecue. I also like the choice it offers. The 310 Sundancer is the only express cruiser of its size that’s available with either inboards or stern drives.

The choice of power has no effect on living space. You get an identical accommodation plan either way. But there is a difference in engine room space. The engines for the stern drives are mounted up against the transom. The drives’ transom plate serves as a rear motor mount and the drive train is all outside the boat. That’s why when you push the button to raise the electric hatch there’s about 4′ separating the engines and the forward bulkhead. This gives you plenty of room to climb in without fear that you’ll step on something you shouldn’t. And once you’re down there, access to the engines is great. Since you’re looking at the front, or “belt,” side of the engines, servicing the water pump and alternator is easy.

Open the hatch on the V-drive installation and the view is dramatically different. The engines are farther forward. There’s only about 2′ of space between them and bulkhead, and that space is occupied by the V-drive’s transmissions. As you step in, the only secure place to put your foot is on the diamond-plate pedestal over the port transmission. From there you have to pick your footing with care.

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The V-drive engines have internal raw-water strainers and an underwater exhaust system, items that are built into a stern drive. These are excellent features, but they consume more space. Things are tight down here. Then, too, V-drive installations require engines to be installed backward. The drive shaft is at the forward end, and the belt side is aft with its water pump and alternator, which are even harder to get at because of the exhaust and mufflers. Most service checks will have to be performed while you’re lying on the cockpit sole alongside the opening – if not atop the engines themselves – while reaching down. And some repairs will force you to disassemble one system to get to another.

Point: This stern drive boat offers a lot more room to work around the engines than its V-drive cousin.

Drive Time

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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.

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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.

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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 ANSWER

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.

Sea Ray 310 Sundancer/V-Drive
speed efficiency operation
rpm knots mph gph naut. mpg stat. mpg n.mi. range s.mi. range run angle sound level
1000 4.6 5.3 2.6 1.8 2.0 319 367 0 65
1500 6.7 7.7 4.3 1.6 1.8 280 322 1 72
2000 8.0 9.2 7.4 1.1 1.2 194 224 4 75
2500 9.6 11.0 12.4 0.8 0.9 139 160 6 81
3000 13.8 15.9 18.1 0.8 0.9 137 158 8 80
3500 20.9 24.1 21.2 1.0 1.1 178 205 6 81
4000 24.8 28.5 26.3 0.9 1.1 170 195 5 84
4500 28.9 33.3 33.4 0.9 1.0 156 179 5 84
4900 31.6 36.4 43.5 0.7 0.8 131 151 4 84
Advertised fuel capacity 200 gallons. Range based on 90 percent of that ­figure. Performance measured with two persons aboard, half fuel, full water. Sound levels taken at helm, in dB-A.
LOA: 33’4″ Beam: 10’5″ Draft: 2’11” Displacement (lbs., approx.): 14,000 Price (w/test power): $184,650 Test boat power: Twin 300-hp MerCruiser 350 MAG MPI Horizon V-8 gasoline V-drive inboards with 350 cid, swinging 18″ x 19″ three-bladed Nibral props through 2:1 reductions.
Sea Ray 310 Sundancer/Stern Drive
speed efficiency operation
rpm knots mph gph naut. mpg stat. mpg n. mi. range s. mi. range run angle sound Level
1000 5.0 5.7 2.8 1.8 2.0 318 366 0 70
1500 6.7 7.7 4.6 1.5 1.7 262 301 1 76
2000 8.3 9.5 7.7 1.1 1.2 193 222 3 77
2500 9.8 11.3 12.2 0.8 0.9 145 167 5 83
3000 14.2 16.3 17.1 0.8 1.0 149 172 7 84
3500 21.4 24.6 19.4 1.1 1.3 198 228 6 85
4000 27.5 31.7 23.0 1.2 1.4 216 248 5 85
4500 33.0 38.0 28.3 1.2 1.3 210 242 4 87
5000 36.6 42.1 36.0 1.0 1.2 183 211 4 88
5300 38.9 44.8 45.2 0.9 1.0 155 178 3 90
Advertised fuel capacity 200 gallons. Range based on 90 percent of that ­figure. Performance measured with two persons aboard, half fuel, full water. Sound levels taken at helm, in dB-A.
LOA: 33’4″ Beam: 10’5″ Draft: 3’3″ Displacement (lbs., approx.): 14,000 Price (w/test power): $184,150 Test boat power: Twin 300-hp MerCruiser 350 MAG MPI Horizon V-8 gasoline stern drives with 350 cid, swinging 22″-pitch Bravo Three ss propsets through 2.2:1 reductions.
Same Power, Different Results: Beyond the stern drive’s obvious speed advantage, it also accelerates harder. Compare the V-drive’s easy straight-line rise in speed to the stern drive’s more aggressive arc.
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