Back in the '70s, most small marine-specific diesels had traditional engineering features such as forward-mounted flywheels and direct injection.

Locating the flywheel forward allowed an engine to be shoehorned right into the bilge of full-keel yachts, where the keel was part of the hull and not simply bolted on to it. The flywheel location also biased engine weight further forward to help keep weight out of the ends of a hull, providing better buoyancy aft and maintaining a more even keel underway.

With their relatively low compression ratios of around 16-17:1, direct injection engines were much easier to hand start than indirect injection diesels which had up to 23:1 compression ratios. Fit the raised hand crank, open the decompression lever(s), crank the engine to sufficient speed, close the lever(s) and providing the fuel was clean and free from water the engine usually started first time.

Increasingly tougher EU and US exhaust emission laws have forced most diesel manufacturers to shift from direct injection in their mechanically-injected engines to indirect injection and heat exchanger cooling to maintain more constant engine temperatures and improve air/fuel mixing in the combustion chambers.

The small direct-injection Volvo Penta and Lister diesels are long gone, the former replaced by marinised industrial/tractor diesels. So when Bukh Diesel Australia supplied me with specs of the Danish-built DV32 ME, the engine was well worth a closer look!

TRADITIONAL ENGINEERING UPGRADED
Bukh's DV32 ME is the up-rated version of its naturally-aspirated DV24 ME counterpart, which has twin cylinders and twin counter-rotating balance weights, direct injection, standard raw or saltwater cooling and a forward-mounted flywheel, just like Norwegian-built Sabb diesels.

As with other Bukh engines, the DV32 ME has a continuous rating output and not the 'A' or intermittent pleasure boat rating of its direct competition.

But in line with Bukh's DV48 ME released some years earlier, the DV32 ME has straight turbocharging to significantly increase power and torque while only marginally increasing engine weight. Power is up from 23.6hp to 31.5hp (at 1.0hp = 746W) from the same 964cc piston displacement with 'square' bore and stroke measurements of 85mm and at the same 3600rpm, yet the dry weight with gearbox has risen only 6kg to 218kg or 226-234kg with optional heat exchanger cooling.

As an indication of how the continuous rating compares with an 'A' rating, consider a Kubota tractor-engine-based competitor. Beta Marine's indirect injection four-cylinder BV1505 develops 37hp intermittent at 3000rpm from its naturally-aspirated 1498cc powerhead but only 29.5hp continuous at the same rpm. But then the BV1505 has a dry weight of 170kg.

The DV32 ME's maximum torque has risen from 57Nm of the DV24 ME at 1800–2100rpm to 68Nm at 2400rpm, although the torque curve is flatter with more torque available in the upper rev range. For example, at 1200rpm the DV32 ME produces 58Nm compared to 52Nm for the DV24 ME, 62 versus 55 at 1500rpm, 65 versus 57 at 1800 and 67 versus 57 at 2100rpm. At 2400rpm the DV24 ME's torque has already fallen to 56Nm and at 2700rpm 53Nm versus 67Nm, while at 3000rpm and 3300rpm the outputs are 52Nm and 49Nm compared to 66 and 64Nm at the same rpm. At the maximum continuous rpm of 3600 the DV24 ME is down to 47Nm whereas the DV32 ME is still producing 62Nm.

The maximum 'A' rating torque of the BV1505 is 95Nm at 2200rpm but at the continuous rating this drops to only 64Nm at the same rpm.

EFFICIENT TURBOCHARGING
Although I don't recommend straight turbocharging for tropical climates due to the substantially higher charge air temperatures than naturally-aspirated or turbo-aftercooled engines, the DV32 ME 'breathes' better than naturally-aspirated counterparts and has a lower mid-range specific fuel consumption, with a minimum figure of 258g per kilowatt hour at 2400-2700rpm from 264 in the same rev range.

Based on a standard prop power curve (not supplied by Bukh), at 2100rpm where the prop is absorbing 9.7hp the DV24 ME consumes 2.2lt/hr, whereas at the same rpm the DV32 ME's prop absorbs 10.7hp resulting in 2.4lt/hr being used. At 2400rpm and 11.8hp the DV24 ME uses 2.7lt/hr compared to 14.7hp and 3.3lt/hr at the same rpm, while at 2700rpm the prop power absorbed is 13.5 and 18.8hp and fuel usage 3.1 and 4.2lt/hr respectively.

At 3000rpm 16.2 and 23.5hp are being absorbed with corresponding fuel usage of 3.8 and 5.6lt/hr, so by these rpm the turbocharger is actually decreasing fuel efficiency. By the time 3300rpm is reached the prop power absorbed is 19.8 and 27.1hp and fuel consumption 4.7 and 6.6lt/hr.

The Wide Open Throttle (WOT) consumption figures are 5.7 and 8.1lt/hr, the latter well above what Bukh quotes for the DV32 ME engine. A 34 per cent increase in maximum power is achieved for a 42 per cent increase in fuel consumption.

Beta Marine does not supply continuous rating-specific fuel consumption figures, so a direct usage comparison between the DV32 ME and BV1505 is not possible.

COMPACT AND SENSIBLE
At 845mm with gearbox the DV32 ME is no longer than the DV24 ME but at 515mm it's 45mm wider. And at 678mm the turbocharged engine is 38mm higher than its naturally-aspirated counterpart, although if an expansion tank for heat exchanger cooling is fitted this adds only 14mm to the DV32 ME's height compared to 52mm for the DV24 ME. The raised hand starting handle adds another 77mm of height to the DV32 ME.

In comparison, with gearbox the Beta BV1505 measures 880 x 499 x 635mm.

The DV32 ME's starter motor is mounted about halfway between the engine bed and rocker cover top, while the 14V, 50amp voltage-regulated alternator is mounted on an adjustable bracket level with the rocker cover. The oil filter is to starboard and very easy to replace and the engine air intake to port is incorporated in the compact turbocharger. A choice of 3:1, 2.5:1 and 2:1 reduction ratios is available.