PMY tests identical Cruisers 400s, one with V-drives, the other with Volvo Penta’s new IPS, to see just how good it really is.
By Capt. Bill Pike — February 2005
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
This article originally appeared in the January 2005 issue of Power & Motoryacht magazine.