Up until a couple of years ago, the maximum saildrive output available was 50hp at the crankshaft. Yanmar and Volvo Penta have since released saildrives (built at the same ZF factory in Italy) capable of handling up to 75hp.
The engines used are either turbocharged (Yanmar) or turbo-aftercooled (Volvo Penta) and develop 73.9hp and 73.7hp respectively. Being powerful and torquey for their weight, they suit maxi racing yachts where the engine and drive weight could be concentrated as close to amidships as possible.
During this period, Italian diesel-engine specialist Iveco quietly released a turbo-aftercooled diesel that developed 80.4hp (where 1.0hp = 746W) at the crankshaft and 73.9hp at the prop in saildrive form, both at 3000 revs. Volvo Penta's D2-75 developed maximum power at the same revs, but the Yanmar peaked at 3800 revs - and at 170Nm (at 2800 revs) it produced nowhere near the torque of its Volvo Penta competition.
Although it had direct injection for better fuel efficiency, the straight turbocharged Yanmar 4JH3-TE had nowhere near the ambient temperature variation flexibility of the D2-75 and its Iveco competition, and at 18lt/h it used two per cent more fuel than the D2-75 at Wide Open Throttle - a result of not burning the air/fuel mix as efficiently.
As I've stated many times in Trade-A-Boat, if an engine is to be turbocharged it should also be aftercooled to lower the charge-air temperature for increased air density and combustion chamber efficiency - which has the additional benefit of cooler exhaust temperatures.
This is important when keel cooling and a dry exhaust system are chosen over heat-exchanger cooling with a wet exhaust.
OUTPUT VERSUS WEIGHT
As with the D2-75, Iveco's 4141 SRM82 is an uprated version of its naturally aspirated four-cylinder 4141 M48 counterpart, which has a piston displacement of 2068cc compared to 2.2lt for the D2-55.
But unlike the D2-55 and D2-75, the M82 develops a lot more power and torque than its M48 counterpart. The maximum power developed is 69 per cent greater, compared to 34 per cent for the D2-75.
The M82's maximum torque is 208Nm at 2200 revs compared to 130Nm at 1850 for the M48 (a 60 per cent increase), whereas the D2-75 produces 212Nm at 1800 revs - up 57 per cent from the D2-55's torque output of 135Nm at 2350 revs.
The additional piston displacement of the D2-75 over the M82 has enabled Volvo Penta to gain slightly more torque, but at much lower revs and across a flatter output curve as is normally the case with turbo-aftercooled diesels.
For example, at 1400 revs the D2-75 produces 198Nm compared to 170 for the M82. At 1600 revs the D2-75's maximum torque is 209Nm whereas the M82's is 184Nm. By the time 2000 revs have been reached, the D2-75 produces 210Nm compared to 204 for the M82 and Volvo Penta's recommended maximum cruising revs of 2500.
Mechanically injected indirect-injection diesels are always cleaner running than their direct-injection counterparts, and to achieve upcoming EU and US exhaust emission regulations, most manufacturers of direct-injection units have switched to indirect.
However, the trade-off is less fuel efficiency across the entire rev range, because although the fuel burns more thoroughly in the pre-combustion chambers, it loses "punch" as it passes through the relatively narrow passages into the cylinders. Another problem is the possibility of cracks occurring between the precombustion chambers and cylinder head - but as the M82 only reaches 3000 revs, this should never happen in normal usage.
Subsequently, when indirect injection diesels are turbocharged and aftercooled, the increases in power and torque are extracted at a substantial price.
At 17.7lt/h the D2-75 consumes 42 percent more fuel at WOT for the 34 per cent power increase over the D2-55, and the M82 a whopping 78 per cent increase or 19.4lt/h for the 69 per cent power increase over the M48.
Based on standard prop power curves (supplied for the D2-75 but not the M82), back at 2600 revs the D2-75 uses 10.3lt/h for 46hp absorbed compared to 8.0lt/h for 34hp - an efficiency improvement of five per cent.
But at the same revs, the M82's prop can absorb 53.6hp and the consumption is 12.1lt/h, compared to 37.5hp and 8.3lt/h at the same revs for the M48 - an efficiency decrease of two per cent.
At 2600 revs, the M82 is one per cent less fuel efficient for the prop power absorbed than the D2-75. Again, I believe this is a result of extracting this amount of power from a 2.1lt mechanically injected powerhead.
HEAVENLY ANGLES
Unlike the M48, which is available as standard with a mechanical straight-output gearbox, the M82 has a TM345A hydraulically-operated box with eight-degree down angle at the output flange.
In many cruising yachts and full displacement cruisers, this enables the shaftdrive M82 to be mounted horizontally, reducing engine height forward.
The TM345A is available with 1.54:1, 2.00:1 and 2.47:1 reduction ratios, and the M82 has a dry weight of 258kg with gearbox - the same as the D2-75 with a mechanical MS25A box. Complete with box, the M82 is 969mm long, 495mm wide and 621mm high, compared to 917 x 544 x 891 for the D2-75.
The Iveco 4141 SRM82+SDMU saildrive version has a 1.92:1 gear reduction, and including gearbox, head is 1038mm long with fibreglass bed measurements of 1036 x 643mm and a dry package weight of 274kg. Volvo Penta's 150S saildrive, on the other hand, has a 2.19:1 reduction ratio the D2-75 weighs 264kg.
The M82 has the same fore/aft and port/starboard inclination angles and all the engine features of the M48, including the saltwater cooled exhaust system - unlike the D2-75's freshwater cooled system. The alternator output is the same at 65amp and 14V, whereas the D2-75 has a 115amp alternator - but at 2.2kW the starter motor has 10 per cent greater output. For more information on the M82, contact Stewart Butler at Lees Industries, tel (07) 3390 5522 or email leesinda-sales@powerup.com.au.