Volvo Penta D1-20

A new contender

A three-cylinder version of its D1-13 counterpart and released in July 2005, the 760cc D1-20 develops 18.5hp (at 1hp equalling 746W) at 2800 to 3200rpm, and like the D1-13 complies with US EPA Tier 2 exhaust emission regulations scheduled for implementation in 2007. It’s suitable for yachts to nine metres or displacement-hulled launches to seven metres.

The D1-20 has all the features of the D1-13, including a cast iron cylinder head and block, high silicon aluminium pistons, hardened replaceable valve seats and heat exchanger cooling with a freshwater-cooled exhaust manifold, and provision for connecting a hot water system. And at 14V and 115 amps, the voltage-regulated alternator has still the highest output of any of the direct competition, although Volvo Penta doesn’t state the starter motor output.

Oddly enough for a current model diesel, the D1-20 doesn’t have a removable cover over the alternator and freshwater circulating pump vee belt, but at least the alternator and starter motor are mounted high on the same side, well above any bilge water. The saltwater cooling pump is gear-driven and glow plugs are fitted for positive cold-starting in low ambient temperatures. The in-line fuel injection pump is driven from the camshaft.

Unfortunately, the torque curve is not flat like the D1-13 and peak output is 47Nm at 2400rpm. The torque rise is rapid from 1200rpm where 40Nm are produced, but the initial peak is 2000rpm and 46Nm with a flat to 2200rpm, then a 'hump’ to 2400rpm. By 2600rpm, the torque is back down to 46Nm and falls off to 41 at 3200rpm.

However, for an additional 18kg, or 16 per cent greater weight, you get three cylinders with significantly lower vibration levels than two cylinders, the ability to handle high alternator loads better at low revs and a peak torque increase of 62 per cent. The combined engine and gearbox dimensions are not much greater, either, with the overall length including an eight-degree down-angle MS10A box being 681mm. At 471mm, the width is actually 17mm less, but at 534mm the D1-20 is 20mm higher.

The three-cylinder heat exchanger-cooled 854cc Yanmar 3YM20 develops 20.9hp, but at 3600rpm, and with a mechanical KM2P-1 gearbox weighs 120kg. Complete with straight-output box the 3YM20 is 693 x 463 x 528mm, so the D1-20 is 12mm shorter, 8mm wider, and 6mm taller. The standard alternator is 60 amps with the option of an 80-amp unit, still way down on the D1-20.

The 3YM20 produces a peak torque output of 50.5Nm from 2200 to 2500rpm, with 48.5Nm available at 1800rpm and 41Nm at 3600rpm.

Based on a standard displacement-hull prop power curve, at 1200rpm where 1hp is absorbed at the prop the D1-20 uses 0.5lt/h, and at 1400rpm and 1.3hp the fuelflow is 0.7lt/h. Increasing the revs to 1600 the power absorbed is 2.4hp and consumption 0.9lt/h. Here the fuelflow curve flattens to 1800rpm, where the figures are 3.1hp and 1.0lt/h. In comparison, at 1800rpm (the lowest Yanmar supplies) the 3YM20’s prop absorbs 2.7hp and the fuelflow is 1.0lt/h.

At 2200rpm, the D1-20’s prop absorbs 5.8hp and the engine uses 1.6lt/h compared to 5.4hp and 1.5lt/h for the 3YM20 at the same revs. At the D1-20’s peak torque hump of 2400rpm, the prop absorbs 7.4hp and the fuelflow is 2.0lt/h compared to 6hp and 1.8lt/h.

the 3YM20’s torque curve starts to drop from 2500rpm, the D1-20’s figures are 8.7hp and 2.4lt/h compared to 6.7hp and 2lt/h for the Yanmar. These revs are also Volvo Penta’s recommended maximum cruising revs for the D1-20.

At 2800rpm and the bottom end of the recommended wide open throttle operating rev range, the D1-20’s prop absorbs 12.1hp and the fuelflow is 3.0lt/h, compared to 9.4hp and 2.6lt/h for the 3YM20. At 3000rpm, the figures are 14.7hp and 3.7lt/h for the D1-20 and 12.1hp and 3.1lt/h for the Yanmar. At 3200rpm and the maximum for the D1-20, the fuelflow is 4.6lt/h compared to 14.1hp and 3.8lt/h for the 3YM20, which has reached the bottom of Yanmar’s recommended WOT rev range. For 13 per cent more power, the Yanmar uses 13 per cent more fuel.

CHOICES, CHOICES
The D1-20 is available with three different transmissions. Suitable for yacht auxiliary installation, especially fin-keel hulls having relatively shallow bilges, the mechanical multiple-disc clutch MS10A box has an eight-degree down-angle at the output flange and is available with 2.35:1 or 2.72:1 ratios. The former is adequate for yachts and the latter better for displacement launches where prop drag is not an issue.

Alternatively, the straight-output MS10L box can be fitted for full-keel yachts having deep bilges, again with 2.35:1 or 2.72:1 ratios and again, being mechanical, the prop can be freewheeled under sail without damaging the gearbox. As with the MS10A, these ratios differ for left-hand props so fitting a pair of D1-20 engines in a cat will create some real propping headaches if opting for handed props.

The 130S Saildrive has a dog clutch and a 2.19:1 ratio and the engine may be mounted ahead or aft of the leg. At 144kg, the Saildrive version of the D1-20 is the same as the similarly-equipped 3YM20.

All versions have an instrument panel, including a start button or key switch, alarm for monitoring engine coolant temperature and oil pressure and alternator charging rate, while a tacho with hour-meter is optional but, in my opinion, essential.

For more details on the D1-20, contact Don Grimes at Volvo Penta Oceania on (07) 3902 5444, or email don.grimes@volvopenta.com.au.