Stern DRIVE VS. V-DRIVE
Which is right for you?
Drive
Train
Boogie
By Kevin Falvey
Photos by Forest Johnson
As seen in
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Powerboat Magazine
boating magazine F E B R U A R Y 2 0 0 7
S
tern 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.
february 2 0 0 7
boating magazine
T
he 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.
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
he 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
T
Sea Ray 310 Sundancer/V-Drive
Sea Ray 310 Sundancer/Stern Drive
speed
efficiency
operation
naut.stat. n. mi.s. mi.
runsound
rpm knots
mph
gph mpg
mpg range range angle Level
1000 1500 2000 2500 3000 3500 4000 4500 4900 4.6 6.7 8.0 9.6 13.8 20.9 24.8 28.9 31.6 5.3 7.7 9.2 11.0 15.9 24.1 28.5 33.3 36.4 2.6 4.3 7.4 12.4 18.1 21.2 26.3 33.4 43.5 1.8 1.6 1.1 0.8 0.8 1.0 0.9 0.9 0.7 2.0 1.8 1.2 0.9 0.9 1.1 1.1 1.0 0.8 319 280 194 139 137 178 170 156 131 367 322 224 160 158 205 195 179 151 0
1
4
6
8
6
5
5
4
65
72
75
81
80
81
84
84
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.)
Price (w/test power) 14,000
Test boat power Twin 300-hp
MerCruiser 350 MAG MPI Horizon
V-8 gasoline V-drive inboards with
350 cid, swinging 18" x 19" threebladed Nibral props through 2:1
reductions.
$184,650
boating magazine F E B R U A R Y 2 0 0 7
speed
efficiency
operation
naut.stat. n. mi.s. mi.
runsound
rpm knots
mph
gph mpg
mpg range range angle Level
1000 1500 2000 2500 3000 3500 4000 4500 5000 5300 5.0 6.7 8.3 9.8 14.2 21.4 27.5 33.0 36.6 38.9 5.7 7.7 9.5 11.3 16.3 24.6 31.7 38.0 42.1 44.8 2.8 4.6 7.7 12.2 17.1 19.4 23.0 28.3 36.0 45.2 1.8 1.5 1.1 0.8 0.8 1.1 1.2 1.2 1.0 0.9 2.0 1.7 1.2 0.9 1.0 1.3 1.4 1.3 1.2 1.0 318 262 193 145 149 198 216 210 183 155 366 301 222 167 172 228 248 242 211 178 0
1
3
5
7
6
5
4
4
3
70
76
77
83
84
85
85
87
88
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.)
Price (w/test power) 14,000
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.
$184,150
w w w. b o at i n g m a g. c o m
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
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 Vdrive. 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
F
boating magazine F E B R U A R Y 2 0 0 7
2-
Stern Drive
1-
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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 Vdrives—ride better in waves and swells because they pitch
less than boats where the engines’ weight is farther aft.
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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.
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 ANSWER
he 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. A
T
w w w. b o at i n g m a g. c o m