Such installations are now commonplace in leisure and commercial applications worldwide.

IPS made its world debut in London amid claims that it represented the beginning of the end for conventional straight shaft technology, which has reached the end of its development life and will be unable to compete in terms of performance, economy, safety, comfort and handling.

The new system is being launched in two variants, IPS 400 and IPS 500, both suitable for twin engine installations in planning hulls ranging in size from 37ft to 50ft and with speed capabilities of from 25 to 45 knots. The systems use 400hp (IPS 400) or 500hp (IPS 500) versions of a 5.5 litre inline six cylinder turbocharged marine diesel with common rail injection which meets future comprehensive emission regulations to be introduced in the EU and USA in 2006-2007.

At launch Volvo Penta is focussing its attention on leisure applications only but, as with Aquamatic, it can be only a matter of time before it crosses over to the commercial marine sector, which already enjoys azipod technology.

IPS is a complete package, including the steering wheel, controls and instrumentation to the engine, propulsion unit and propellers. The engines are coupled to steerable propulsion units and a pair of forward facing propellers. The propulsion units are mounted on the underside of the boat slightly forward of the transom in specially designed holes integrated into the hull structure. Although the public launch has been in London, a number of well known builders worldwide have been developing IPS models to be available for this spring's round of boat shows, either IPS versions of existing boats or totally new models designed around IPS.

The IPS design results in very high efficiency. The propellers face forward and the propwash (into which the exhaust is emitted and carried well behind the boat) is absolutely parallel to the bottom of the boat so that all power developed drives the boat forward, while the twin prop concept with counter-rotating propellers cancels out rotation losses.

Volvo Penta has comparison tested the new system in two identical Cranchi 41 Mediterranee model boats, one fitted with twin IPS 500s and the other with twin TAMD63P engines with conventional straight shafts. The engine output was the same in both boats, 2 X 370hp.

The IPS boat achieved a 20% higher top speed, 15% better acceleration, 30% better fuel consumption and a noise level some 50% lower at the helm.

Also improved was straight lie stability, a much tighter turning radius at speed, and much better low speed manoeuvrability in congested harbour environments.

MJ Information No: 20227