Talking Torque: Big Revs and Big Space

Torquey, compact and fuel efficient, Volvo’s D4 230 is the four with more.

For old farts like me, the concept of powering a trawler yacht with a relatively high-revving engine is at odds with my beliefs. 

In trawler yachts such as the Island Gypsy 32 from the ‘80s, there would normally be a single straight-six Ford diesel pumping out 120hp at a lazy 2500rpm.

As trawler designers strived to provide more accommodation in hulls of this length, the answer was to swap sixes for fours.

An example of this development is the Integrity 340SX, that manages to squeeze in another cabin opposite the head by fitting a four-cylinder diesel instead of a straight-six unit. 

Not a traditional naturally aspirated diesel spinning at 2500rpm, but a compact direct-injection Volvo Penta D4 230 that develops maximum power at 3400rpm.

This is up from its original output of 206 brake horsepower at 3500rpm when the engine was first released in Australia in 2003.

Sure, these are high revs, but for the market the 340SX is designed to capture — couples and young families who may have chosen the easier life of a trawler over a sailing yacht — diesels revving to 3400 and even higher are commonplace.  

Only in the past decade have manufacturers of yacht auxiliary diesels started offering engines that peak at 3000rpm instead of 3600.

Meanwhile, the torque and power the D4 develops compared to the old fours is simply amazing. 

The 3.9L naturally aspirated direct-injection Perkins 4-236 for example, developed 250 Newton Metres at 1600rpm and 76 brake horsepower at 2250rpm, whereas the 230 develops a whopping 580NM at 2000 to 2600rpm, with 300NM available at a low 1000rpm.

THE NITTY GRITTY

The 230 has many advantages over the old mechanically controlled diesels, such as 

plug-in diagnostics for engine running issues through the Engine Management System (EMS) and off course, engine protection from idiotic owners.

One of these is the automatic limitation of engine revs to 1200rpm until the engine has reached normal operating temperature. 

Another feature is when using woeful local distillate of 840gm/L, the EMS will maintain constant torque and power output from 5–55C, so engine performance won't diminish in tropical climates.

Like most modern high-speed diesels, the five main bearing 230 has four valves per cylinder, operated by double overhead camshafts, but joy, oh joy, hydraulic valve lifters are fitted, eliminating valve clearance checks providing the engine oil and filters are changed at the prescribed intervals (every 200 hours).

Most other engine manufacturers that shall remain nameless use ‘bucket and shim’ valve clearance adjustment that requires removal of the camshafts to access the shims, a complex and expensive task. 

Another unusual feature of the 230 is its twin harmonic balance shafts to reduce imbalance inherent in four-cylinder four-stroke engines. 

But sensibly for a marine engine, the cylinder block and head are cast iron, with freshwater cooling of the turbo-charger and aftercooler, a safer arrangement of cooling than raw or sea water should gaskets fail.

QUALITY SPECS

In line with commercial engine design, the 230 has twin canister oil filters alongside the water separating fuel filter. 

The electronic common-rail fuel management system delivers fuel at a massive 2000bar or 29,400psi.

Standard is a 12V 150A voltage-regulated alternator although a 24V alternator is optional.

Eight-degree down-angle hydraulic gearboxes are standard, enabling the engine to be mounted level in most displacement hulls that have relatively shallow shaft angles compared with planning-hulled inboards. 

Volvo Penta's Electronic Vessel Control or EVC provides electronic throttle and shift control for ‘clunk-free’ operation and reduced maintenance. 

A nice touch of all the gearboxes on offer is that the prop shaft can freewheel for up to 24 hours at a time without fear of insufficient box lubrication — a useful feature for engines installed in yachts or when twin engines are installed and the owner wants to run on one engine to save fuel.

Complete with ZF box, the 230 is 1234mm long, 848mm wide and 794mm high, so it’s not a bulky engine for its torque and power outputs. The complete dry weight is 565kg.

Although Volvo Penta doesn't stipulate recommended oil viscosity in its tech specs, I suggest using a diesel-specific SAE 15W40 oil and change the oil and filters every 200 running hours or every six months, as turbo aftercooled engines are intolerant of dirty oil. 

ON THE WATER.

In Trade-a-Boat October 2019, John Ford reviewed an Integrity 340SX powered by a 230 running a 2.52:1 reduction ratio to reduce prop speed to a thrust-efficient 1350rpm. 

This demo boat was slightly over-propped with the engine reaching only 3280rpm, but in a displacement hull, slight over-propping isn’t an issue as the engine is unlikely to be run continuously above 2600rpm, the upper end of the torque peak.

As with all displacement hulls, the fuel flow rose significantly when the hull was pushed past its hull speed of around 7.5kt.  

Even though the 230 has electronic injection control and shouldn't suffer cylinder bore glazing from fuel over-supply and light loads that afflict mechanically-injected diesels, I still recommend not running the 230 continuously below 2000rpm or the start of the torque peak. 

In the Integrity 340SX, this equated to 7.4kt using 11L/h, only 26 per cent of maximum fuel flow in this hull.

Back in 2009, I helped a mate deliver his Lagoon 38 sailing cat from Brooklyn on Sydney's Hawkesbury River, to Lake Macquarie. 

With the twin Yanmar 30 diesel saildrives running at 2700rpm, we averaged 6.5kt over ground against a 10–15kt nor'easter up the Central Coast.

Though slow compared to motor cruisers I've delivered, the speed allowed us to cover distances without taking forever, while maintaining an easy motion and no hull slamming against waves. 

So cruising offshore at 6–7kt is actually very pleasant. 

Set up waypoints in the autopilot, then sit back and enjoy the voyage as we did that day.

THE WRAP

The benefits of fitting a relatively small displacement diesel in a displacement trawler yacht more than outweigh the drawbacks, especially when accommodation space is so much greater. 

The 230 has features that should ensure a long, low maintenance lifespan. 

Just make sure it's propped to reach its designed revs or slightly above, under normal hull loading. 

For more on the D4 230, find your local Volvo Penta centre via the Dealer Search Page: volvopenta.com/marineleisure/en-en/contact/local-dealer.html.

QUICK SPECS

MAKE/MODEL Volvo Penta D4 230

TYPE Four-cylinder DI CR aftercooled turbodiesel

BHP/MHP* 226.5/229.8 at 3400rpm

PEAK TORQUE 580NM at 2000–2600rpm

DISPLACEMENT 3670cc

DRY WEIGHT 565kg  

*Brake horsepower/metric horsepower or PS