Cummins' Quantum System

For buyers of larger craft wanting to specify low-pollution diesels as part of a new boat package or owners intending to re-power existing hulls with the latest in marine diesel technology, there's now a large selection of electronically-managed engines from which to choose.

Latest on the scene is the Cummins QSM11, a powerplant suitable for larger craft, based on the direct-injection M11 diesel introduced to the trucking industry in 1993.

Known as the QSM11, the marine version went into production in April. It has been designed primarily for recreational planing hulls, around 11m in single installations and 13m in twins.

Research conducted by Cummins Marine shows that typical owners will only clock-up approximately 300 operating hours per year. But even so, on-the-water tests proved the engine reliable for more than 4800hrs. In addition, the QSM11 has a cylinder head, pistons and turbocharger designed specifically for marine operation. Even small items such as the saltwater pump impeller have been modified for easier replacement in marine installations.

KEEPING IT SIMPLE
Cummins Marine's new offering is designed to compete directly with the direct-injection electronically-managed diesels from Cat Marine, Detroit Diesel, MAN and Volvo.

It's a turbo-intercooled 10.8lt straight six that develops 635hp at 2300 revs for recreational applications and 580 at the same revs for light commercial operation. Maximum torque is 2332Nm at 1700 revs (average output 280hp and consumption 50lt/hr) and 63.8% of this is developed at only 1150 revs.

The QSM11 is relatively simple (by low-pollution marine diesel standards), and has a counter-flow (non cross-flow) cylinder-head for excellent fuel injector, filter and Electronic Control Module (ECM) access. It has reliable pushrod valve actuation and 12 valves, and standard are a seawater-cooled aftercooler and dry exhaust manifold. To further reduce emissions, a closed crankcase breather system is used.

According to Cummins, testing has shown that black smoke on initial start-up is limited to 30-60secs well down on the three-minute maximum expected by most recreational boat owners. Once warm, there was no smoke at any time.

Another aspect again, according to research conducted by Cummins reveals that at idle speeds, potential buyers did not want to hear or feel any vibration through the boat. Cummins claim from 550-700 revs this has been achieved.

SIGNIFICANTLY CLEANER
In comparison to the Cummins powerplant's 635hp, its closest competition, the 12lt Cat 3196, develops a maximum output of 660hp at 2300 revs and develops 2940Nm at a low 1400 revs.

According to Cummins, the QSM11 has a maximum fuel consumption of 123lt/hr, compared to 125 for the 3196. And from sighting engine performance/emission curves, it appears significantly 'cleaner' across the entire rev range, with only a fraction of the Cat's emissions when passing the planing 'hump' at around maximum torque revs.

Where the QSM11 really scores over the 3196 is with its compact dimensions. In bobtail form (sans gearbox), it's only 1293mm long, 978 wide and 978 high the last dimension very low for a diesel of this output. In comparison, the 3196 is 251mm longer and 30 higher, but 12mm narrower and, at 1177kg, weighs 55 more.

Surprisingly, for a four-stroke engine, the QSM11 is much more compact than the V-six Detroit 6V92-TTA DDEC. Although the QSM11 displaces 1.75lt more and develops 10hp more at the same revs, it's 191mm narrower and lower only losing out in length where it takes up 99mm more. The 6V92-TTA weighs 145kg more and has has a WOT consumption of 121.8lt/hr.

What these comparisons indicate to me is that, for diesels under 800hp, the straight six configuration remains the best compromise between installation space required, maintenance and servicing access. And, of course, low weight.

MAXIMUM TORQUE
Truck diesels such as the QSM11, which develop maximum torque at relatively low revs, lend themselves perfectly to the range of two-speed manually-controlled, but electronically-shifted gearboxes now available from ZF. For readers unfamiliar with the ZF two-speed concept, the engine is kept in first gear to allow the engine to quickly reach its torque band, then once the boat is planing it's shifted (usually at around maximum torque revs) to high gear to reduce engine speed.

The result is not only reduced fuel consumption and noise while planing, but in conjunction with carefully selected props also better low-speed boat control due to less engine load and, subsequently, a more throttle-responsive engine.

According to Cummins, one problem facing marine diesel manufacturers is that some planing-hulled boat owners throttle up through mid-range revs up onto the plane, instead of quickly planing the hull, then throttling back once up. A ZF box would help reduce engine wear by allowing the motor to rev freely until the boat is planing, then shifted up once the hull is up and engine load reduced.

For both recreational and light commercial applications, ZF's IRM 350 ATS, which has a 7? down-angle at the gearbox output flange, would suit the QSM11. This adds 746mm to the overall length and weighs 325kg.

Cummins Marine's Quantum System is an electronics pack age, which includes the ECM (mounted high up on the port side), electronic sensors that process engine operation every 20 milliseconds, diagnostics with servicing connection, engine speed control and analog displays (multi-station if needed).

The optional C-Cruise package includes a marine cruise control (according to Cummins, the only one in the industry), alternate/custom slow idle, twin-engine synchronisation, interactive digital engine function displays and back-up throttles should the control-by-wire system fail.

With the slow idle function, engine speeds can be OEnudged' up or down by as little as 25 revs for precise low-speed control.

On examination, Cummins Marine's QSM11 is compact, fuel efficient and clean running. It is a welcome addition to the electronically-managed marine diesel market.

For more information, contact Shane Murphy at Cummins Marine, tel (03) 9765 3222.