Beta Marine BZ482 and BD722

Though not new, according to UK-based Beta Marine the BZ482 and BD722 still comply with current and upcoming EU and US exhaust-emission regulations.

Both have power and torque output-to-weight ratios that are more than a match for some of the better-known competition. The smaller model suits yachts to eight metres and displacement-hulled cruisers to six, while the larger can handle yachts up to nine and cruisers to 7.5m.

Cleverly, Beta Marine supplies potential owners with both intermittent or "A" rating and maximum continuous ratings for its engines. The "A" rating is pleasureboat usage only where no more than 300 operating hours are clocked up in any one year, and during any one period the engine is run at less than 10 per cent of the time at Wide Open Throttle. Maximum continuous cruising revs at this rating are 3000.

With these little engines the continuous rating is intended for inshore work and fishing boats, and presumably it compares to a "C" or medium-duty rating for a maximum of 3000 hours per year with less than 25 per cent of that time at WOT.

LIGHTWEIGHT & FUEL EFFICIENT
Both engines have the same 67mm cylinder bore and 68mm piston stroke, and the BZ482 has a piston displacement of 478cc and the BD722 719cc.

At 89kg including Hurth mechanical gearbox with axial (straight-line) output, the BZ482 is beaten only by Yanmar's 1GM10 for weight - 76kg with box. But then for a 17 per cent higher weight, the Beta engine has heat-exchanger cooling versus raw water, two cylinders instead of one and 50 per cent greater piston displacement, which enables it to develop 50 per cent more power at the same revs.

Based on 1.0hp = 746W, the BZ482 develops 13.3hp intermittent and 10.9hp continuous at 3600 revs, while the maximum intermittent and continuous torque outputs are 28.8Nm (60 per cent over the 1GM10) and 19.8Nm respectively at a low 2600 revs.

Based on a standard intermittent prop power curve (not supplied by Beta Marine) at 2200 revs where maximum torque is 27.9Nm and the prop is absorbing 4.9hp, the BZ482 consumes 1.1lt/h; 5.6hp and 1.2lt/h at 2400 revs; 6.8hp and 1.4lt/h at 2600 revs; 8.0hp and 1.7lt/h at 2800 revs; and 9.4hp and 2.0lt/h at 3000 revs.

From here as the prop power curve approaches the maximum output curve, the fuel consumption rises significantly and at 3200 revs and 10.7hp the average usage is 2.4lt/h; at 3400 revs and 12.1hp it's 2.8lt/h.

The WOT consumption is 3.2lt/h, which is still reasonable considering the engine is capable of producing 25.2Nm at these revs.

The three-cylinder BD722 develops slightly more power at the same revs but 20 per cent more torque than Yanmar's twin-cylinder 2GM20 from its 13 per cent greater piston displacement. Yet at 106kg, it weighs the same as the raw-water-cooled Yanmar, whereas the heat-exchanger version is eight per cent heavier.

The BD722 develops 22.7hp intermittent and 16.0hp continuous, both at 3600 revs, and the maximum intermittent torque is 43.2Nm and continuous torque 28.8Nm - again both at 2600 revs and 55 and 45 per cent over the BZ482.

Based on a standard intermittent prop power curve (not provided by Beta), at 2200 revs and 40.5Nm with a prop horsepower absorption of 7.1, the average fuel usage is 1.6lt/h; at 2400 revs and 8.1hp it's 1.9lt/h; at 2600 revs and 10.1hp 2.2lt/h; at 2800 revs and 12.1hp 2.7lt/h; and at 3000 revs and 13.7hp it's 3.1lt/h.

Interestingly, as the revs increase out to WOT the specific fuel-consumption rise is not as steep as the BZ482, and at 3200 revs and 16.0hp the average fuel usage is 3.6lt/h; at 3400 revs and 18.0hp it's 4.1lt/h.

The WOT average is 5.2lt/h with 36.9Nm of torque still being produced, so for a 70 per cent increase in intermittent power over the BZ482 the fuel consumption has risen 63 per cent.

SENSIBLE ENGINEERING, CHOICE OF SUMP DEPTHS
These little diesels have to compete with comparable offerings from IVECO, Nannidiesel and Volvo Penta, and there's no doubt that Beta Marine has put a lot of effort into marinising them, sensibly using proven and very reliable Kubota base engines that now have been around for at least a couple of decades.

Both have gear-driven camshafts with pushrod OHV layout and cast-iron cylinder blocks and heads with heat-exchanger cooling for reliability and longevity.

Kubota's TVCS ("Three Vortex Combustion System") is used to reduce combustion noise and increase air/fuel combustion efficiency. Glow plugs are fitted in the precombustion chambers for easier cold starting below five degrees of ambient temperature, and the heat exchangers have Cupro Nickel tube stacks and Phosphor Bronze end caps with a replaceable zinc anode for longevity.

The starter motors and alternators are mounted well above the engine beds and away from any bilge water, although Beta Marine should fit drip shrouds over the alternators in line with the direct competition. The company doesn't mention the standard alternator output but a 55amp unit is optional.

The alternator and freshwater circulating pump are driven via the crankshaft pulley by a rubber vee-belt that appears very easy to replace.

Unusually, Beta offers a choice of two sump depths - one 64mm deeper for less possibility of oil-pump starvation when motorsailing. A brass sump drain pump is standard on both engines. Static installation angles are 15° fore and aft and up to 25° of heel port or starboard for motorsailing.

Oddly enough for a company that presents such a copious amount of technical information in its engine brochures, no mention is made of gearbox ratios - but based on the similar Hurth boxes used by the direct competition, the reduction ratios should be between 1.5 and 2.5:1.

The engines have compact dimensions, and including gearbox the BZ482 is 560mm long, 438mm wide and 526mm - or 590mm depending on sump depth - while the BD722 is just 70mm longer with all other measurements the same.

The Beta Marine lineup comprises nine naturally aspirated, indirect- injection diesels from 13.3 to 61.1hp, all based on Kubota tractor engines.

For more information, contact Beta Diesel Australia, tel (02) 9525 1878.