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Volvo’s new propulsion package

The Inboard Performance System incorporates some unconventional features, like forward-facing props

When a company such as Volvo Penta sends an invitation to attend the international unveiling of its new Inboard Performance System, one can only imagine what the company has been up to.

I attended the product debut in Mallorca, Spain, in October and can appreciate Volvo’s enthusiasm for the new propulsion system. To start things off, we viewed an in-water demonstration that compared two Cranchi Mediterranee 41-footers, one fitted with the new twin IPS 500s and the other with twin TAMD63P engines using conventional straight shafts.

The impressive performance difference between the two vessels caught everyone’s attention. We would have our turn test-driving the boats over the next few days to fully experience the differences for ourselves. (Volvo provided eight different test vessel platforms.)

IPS is a complete package, from the steering wheel, controls and instrumentation to the engine, propulsion unit and propellers. Although other manufacturers offer “complete” propulsion packages, Volvo has raised the bar considerably with its IPS 400 and IPS 500 systems. They are designed for twin-engine installations only, and suited for planing hulls ranging from 37 to 50 feet and upward.

Maximum design speed is from 25 to 45 knots. Volvo engineers work closely with boatbuilders to ensure each IPS installation is optimized for the characteristics of the intended vessel, thus assuring optimum performance.

The original concept for the Inboard Performance System began in 1997, with the official approval to begin development in August 1999.

IPS features

A basic description of the system should begin with the propulsion unit, which resembles a conventional sterndrive or outboard-engine lower gear case below the waterline. The unit is installed through the bottom of the hull in a specially designed structure integrated into the boat during construction. The lower unit mates with the transmission and steering section, installed from above, and the two components are secured to the mounting collar with a locking flange. Watertight integrity is achieved with two substantial captive O-rings.

The drive is mounted slightly forward of the transom, coupled to the inboard diesel with a short shaft and electronically controlled from the helm.

The propulsion unit eliminates the numerous conventional through-hull penetrations normally associated with an inboard engine installation: shaft log, shaft strut mounting, rudder post, seawater intake and engine exhaust. The IPS steerable drive installation incorporates the seawater intake, cooling water discharge, exhaust discharge, and directional control through a single hull opening per engine.

Another unconventional feature of IPS is twin forward-facing propellers. This design results in very high efficiency, as the propeller functions in undisturbed water and backwash is absolutely parallel with the bottom of the boat. All of the power that is developed drives the boat forward, unlike conventional inboards that tend to push the bow down due to the thrust angles of the shaft.

Each propulsion unit incorporates twin counter-rotating props that cancel out rotational losses. This system also provides for below-the-waterline exhaust, which quiets vessel operation considerably.

The steerable propulsion units enhance vessel maneuverability when compared to a conventional straight inboard shaft drive. With a conventional inboard system, the rudder can direct only a portion of the propeller backwash, while most of the propeller thrust continues to move the boat forward. With IPS, when the propulsion units are turned, all propeller backwash and full thrust are turned in the desired direction.

The dramatic difference in maneuverability is immediately obvious upon leaving the dock. Steering is electronically actuated and progressive, meaning it’s easier to turn the wheel at slower speeds. At high speeds, IPS provides enhanced straight-line stability, but also reacts quickly to driver input and has a very tight turning radius.

Consistent with Volvo’s thorough engineering, the turning radius and rate are governed by vessel speed to help avoid dangerous situations. When running at wide-open throttle and turning the wheel hard over, the electronics will limit the turning radius. As the throttle is backed down, the turning radius decreases proportionately. The changes in vessel speed and turning radius are seamless and, unless you are paying careful attention, go mostly unnoticed. It was only after several high-speed maneuvers that I realized the changes that were occurring.

Improved passenger comfort can be attributed to the fact that the propulsion unit installation absorbs the propulsive and steering forces, and enables the engines to be soft-suspended for further vibration reduction. The unit also acts as exhaust pipe and noise damper, expelling combustion gases into the propeller backwash beneath the boat, and reducing unpleasant combustion odors, fumes and noise on board. While seated on the aft bench there was an obvious decrease in noise and fumes with the IPS-equipped boat.

The entire system, from steering wheel to propulsion units, is electronically controlled and integrated with Volvo Penta’s EVC electronic control platform.

In terms of performance, IPS generally provides a 20-percent higher top end, 15-percent increase in acceleration, and 30-percent improvement in range compared to conventional straight-shaft installations, according to Volvo. In addition, the turning radius is 50 percent tighter, and the boats perform with less noise and vibration. Volvo technical data indicates that an IPS 400, which uses the 310-hp D6-310 engine, corresponds to conventional inboard engine output of about 400 hp. The IPS 500 with its 370-hp D6-370 engine compares with a 500-hp inboard engine output.

Maintenance and emissions

Servicing the Inboard Performance System should prove to be straightforward compared to conventional outdrives or straight-shaft inboards, as there are no tilt, trim or steering joints to be concerned with and the issue of leaking bellows doesn’t exist. The IPS steering motor is maintenance free, according to Volvo. There are no packing glands to deal with for periodic maintenance or adjustment, and access to the in-hull components is straightforward.

Volvo says IPS will meet future comprehensive emission regulations to be introduced in the United States in 2006-’07. Numerous foreign and domestic boatbuilders already are in production using IPS. U.S. builders on board in mid-December were Cruisers, Fairline, Four Winns, Regal, Sealine and Tiara.

Damage control

In the event of a severe high-speed impact to the propulsion unit (hard grounding), the underwater components will shear off flush with the hull, and the lower bearing carrier is engineered to break at a point below the O-ring seal separating the fixed and steerable parts of the drive. Although the entire propulsion unit will require replacement, Volvo says the hull will remain watertight.

After viewing and testing IPS, I am convinced that Volvo Penta has done its homework and produced a truly innovative propulsion system. The acceleration and handling differences were impressive comparing the two Cranchi 41s, and no test instruments were required. In the April issue I’ll review the Volvo Penta Inboard Performance System in greater detail.

Volvo Penta, Chesapeake, Va. Phone: (757) 436-2800.