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Toward the end of last
summer, I flew from Florida to Oconto, Wisconsin—home of Cruisers
Yachts—to examine and test one of the strangest boats I’d
ever seen: a deckless 400 Express with a propulsion system so top-secret
I wasn’t supposed to write about it, photograph it, or even mumble
about it in my sleep.
The sneak peek the folks
at Cruisers had arranged for me was part of a joint project with PMY
and Volvo Penta, the point being to independently compare and verify performance
data on two identical 400s—one with conventional V-drives and the
other with Volvo Penta’s new Inboard Performance System (IPS)—a
few months later, in December, at the Cruisers facility in Wilmington,
North Carolina. Both Cruisers and Volvo Penta felt a brief, preliminary
spin on Lake Michigan at the helm of the IPS-equipped 400 made sense,
given the complexity of the story I was to write for this issue, which
coincides with the intro of IPS at the Miami International Boat Show.
There were just two caveats. First, I had to bear in mind that the boat,
with her unique IPS-modified stringer system (with integrated mounting
rings) and running surface (with a keel pad instead of a keel and no propeller
tunnels), was not performing optimally. And second, mum was the word.
I jumped onboard the
400 at a marina near Oconto. Except for aluminum stiffeners mounted athwartship
at the gunwales, the hull of the 400 Express was open to the sky. Beneath
my deck shoes was a rough, plywood steering station undergirded with two-by-fours.
On the leading edge of the station was a makeshift dashboard, also of
plywood, jury-rigged with ignition keys, single-lever Volvo Penta electronic
engine controls, and a wheel. Abaft the station in the machinery spaces
was what I’d come to see: a matched set of IPS 500s. Volvo Penta
was planning to market just two twin-engine versions of IPS at first,
one with 310-hp D6-310 diesels (the IPS 400) and the other with 370-hp
D6-370 diesels (the IPS 500). Our boat had the brawnier package.
I fired up the mains
and headed for Lake Michigan, which was awash in two-footers at the time,
with maybe a three-footer thrown in now and again. IPS impressed me immediately—the
turning radius of my test sled was so tight, I passed on spinning the
wheel hard over at full-throttle for fear of tossing somebody into the
drink. Top speed was rousing, as was acceleration. I was mightily impressed
with the boat’s tracking. It was superb both at speed and while
going slower in the marina, even on one engine. And there was virtually
no vibration. The 400 ran like a Swiss watch—or, more accurately
perhaps, a Swedish one.
Docking was a tad problematic,
though. For starters, I tried backing the 400 into her slip as if she
were a conventional stern drive, meaning I shifted the engine controls
astern, with the throttles at dead idle, and used the wheel to direct
the IPS drives as well as the boat. I failed several times. “Dang,
Todd,” I remarked to Cruisers propulsion engineer Todd Trepanier,
who was next to me. He suggested I try handling the boat like a conventional
inboard, meaning with throttles and shifts alone and the underwater units
centered. I did and succeeded on the first try, albeit clumsily. Later
that night I spent a few hours in my hotel room, drawing vector diagrams
in a notebook, trying to figure out why IPS boat handling seemed sorta
idiosyncratic.
Months passed. Then
in December I revisited my sneak-peek 400 Express, although this time
she was in a complete, decked-over state with a full interior, all auxiliary
components installed and her IPS-500 units tested and tweaked. She was
also lying alongside an identical sistership with conventional, twin 370-hp
D6-370 diesel V-drives. Volvo Penta was claiming 20 percent higher top
speeds and 30 percent better fuel economy for IPS, based on in-house testing.
Would our long-awaited comparo validate these amazing numbers?
It was showtime!
I drove both test boats
under identical conditions—fuel, water, waste, number of people
onboard, and sea state. As you can see in the accompanying test results,
I generally recorded significantly better numbers for IPS, but they weren’t
quite up to those touted by Volvo Penta.
For example, our IPS
boat’s top speed was 41 mph, while top speed for the V-drive was
36.4 mph, an increase of 11 percent. Moreover, the greatest disparity
in speed occurred from 3000 to 3500 rpm, where IPS registered an extra
3.9 to 4.9 mph. Again, the 12-percent gain for IPS was well under Volvo
Penta’s claimed 20 percent.
Next page >
Part 2: The speed and other performance enhancements I recorded during my comparison test speak for themselves. > Page 1, 2,
3, 4, 5
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