Yacht Auxillaries - Part Two

You can please some of the people some of the time... Last issue we kicked off our look at popular (inboard) yacht auxiliaries with the pros and cons of sail versus shaft drives.

Much to the chagrin of all but one of the major players in this marketplace we used a Volvo unit to contrast some of the aspects of these installations. This issue we look at a cross section of the more popular powerplants currently available within this market segment Down Under.

The range of small diesel engines available to boaties even within a relatively small market like Australia is quite surprising. In addition to the well-known manufacturers featured here Volvo Yanmar, Bukh and Nannidiesel there are a considerable number of other companies supplying and marinising new and used industrial diesels for use in yachts.

While some of these units potentially offer very good value for money, purchasers should be cautious when taking the plunge.

In short, my advice is to look around and check out what your fellow yachties are using. And if you are looking at a 'new' brand then why not ask to speak to some earlier purchasers of the products.

The saltwater environment is nothing if not punishing doubly so in the confines of the average yacht bilge.

VOLVO
In its 'compact diesel' range Volvo offers six different models, each available in sail or shaft drive versions. All motors are freshwater cooled with indirect injection and comply with tough European exhaust emission laws for diesel engines. All are compact and smooth-running with a number of interchangeable components.

Alternatively, the MS2A gearbox has a 7? down angle at the output shaft and the choice of 2.4:1 or 3.0:1 ratios, while the straight-output MS2L box has a 2.3:1 ratio. All boxes have cone clutches with mechanical actuation for reliability.

YANMAR
Japan's largest manufacturer of small (up to 5000hp) diesel engines, Yanmar diesels are known worldwide for reliability in both recreational and commercial applications. For example, most of the local professional fishermen on Lake Macquarie (NSW) use Yanmar diesels, simply because downtime with their engines is minimal.

Commanding over 50% of the Australian saildrive market another desirable factor is the availability of Yanmar spares right across the Pacific region.

Unlike the Volvos, raw-water (saltwater) cooling is standard below 30hp and only the twin and three-cylinder models have the option of heat exchanger cooling. Above this output all the motors have direct injection for easier cold starting. It should be noted that theoretically exhaust emissions are greater because a naturally aspirated (non-turbo) direct injection diesel will always be 'dirtier' than an indirect injection unit.

On the flip side, Volvos such as the four-cylinder MD22 are derived from automotive units and have belt-drive overhead camshafts, whereas the equivalent Yanmar has a marine background and retains pushrod valve actuation.

Personally, for ultimate reliability I prefer Yanmar's system, but with fewer moving parts the Volvos are smoother-running at higher revs.

Yanmar offers the choice of saildrives or shaft drives with mechanical gearboxes on all motors to 62hp.

There are two saildrive units, one for motors to 30hp and the above for larger engines. Both models have two sealing diaphragms with a sensor between them which sounds an alarm in the cockpit should water penetrate the main diaphragm.

The smaller SD20 drive unit has a 2.64:1 gear ratio, while the larger SD31 has a 2.31:1 ratio.

One point worth considering is that Yanmar's drive design is reversible. The powerplant can be mounted ahead of or astern of the saildrive leg.

Shaft drive motors to 30hp are available with either the KM2P mechanical box or KM3V mechanical V-drive unit. Even with the single cylinder 1 GM10 the choice of ratios is vast, from 2.21-3.22:1 for the KM2P and 2.36-3.20:1 for the KM3V.

Motors over 30hp are available with a choice of two straight shaft drive boxes, one of these having a 7? down-angle on the output shaft. Between the two boxes there are six ratio options, from 2.14:1-3.21:1.

All Yanmar shaft drive gearboxes have lower astern ratios than forward ones, allowing the motor to reach its torque band faster when manoeuvring.

To compare directly with the Volvo motors listed, all Yanmars below are freshwater cooled (where applicable). Saltwater cooled motors (up to 30hp) are 8kg lighter. V-drive motors are 13kg heavier than their straight shaft-drive counterparts.

Yanmar claims its units offer the best power to weight ratios in the marketplace and also notes that they offer emergency handcrank-starting. The TCE models are turbocharged (though not intercooled).

BUKH
Like Yanmar, Bukh is quick to point out that it still manufactures true marine engines. According to Bukh, Nannidiesel (up to 62hp) and Volvo (up to 29hp) use automotive base engines which are designed to operate at higher temperatures than marine engines and so must be freshwater cooled. Made in Denmark, Bukhs are built in the traditional yacht auxiliary way (as were the older Volvo range) and are somewhat less complex than the competition. The 24, 36 and 48hp models have forward-mounted flywheels (like earlier Volvos), enabling the shaft drive versions to be shoehorned deep into the bilges of full-keel yachts, placing the motors away from accommodation.

The forward flywheels also group the starter motors and alternators up front and well above the crankshaft line for ease of servicing and better protection from bilgewater than most of the competition. All Bukhs are raw-water cooled for simplicity, though heat exchanger (freshwater) cooling is available for the 24-48hp models for yachties who want hot water take-off. The heat exchanger adds about 15kg to the overall weight.

All Bukhs have direct injection for easier handstarting back-up. Based on my Merchant Navy experience of handstarting direct-injection Lister lifeboat and fire pump diesels up to 1655cc, I can see no problem doing this with all the Bukh models. This starting ease is reflected in the range of lifeboat diesels Bukh also makes for the European market.

Whether the saltwater-cooled direct-injection Bukhs comply with European exhaust emission standards was not known when compiling this guide in late January. We'll let you know down the track!

As Bukhs are true marine engines, they are all rated continuously at the prop, not at the flywheel as with other brands. Continuous rating gives a real indication of an engine's output, much the same way that all automotive engines have been rated since the late '70s.

Admittedly, the 24-36hp models weigh more than the competition, but some might consider that's the price you pay for traditional cast iron engineering.

Bukh makes the only turbocharged diesel in this guide under 50hp. Though designed more for light to medium displacement yachts, the DV48ME offers a 33% power hike over the naturally-aspirated DV36ME, yet weighs just 12%.

Shaft drive Bukhs are available with a mechanical gearbox and a choice of 2.0:1, 2.5:1 or 3.0:1 ratios.

Saildrive ratios are 1.75:1 for the DV10LSME (which is also the lightest saildrive diesel currently available) and 2.25:1 for other models.

Note: Bukh Diesel Australia also markets a range of Beta Marine Diesels, from 10-62hp in the yacht auxiliary range. All are freshwater-cooled, based on the same diesels used by Nannidiesel and are marinised according to Lloyds of London's specifications.

NANNI DIESEL
Nannidiesel base engines are designed for constant, heavy duty usage and are part of a worldwide network of more than 450 service agents. The base engines are marinised in France.

All models are supplied complete with gearbox, freshwater-cooled exhaust manifold with wet exhaust (injection) elbow, instrument panel (including a tacho on some models), flexible mountings and toolkit. Alternators are mounted high on the engine away from bilgewater, as are starter motors on the 4.220HE and 5.280HE. And to meet strict European exhaust emission standards, all models up to 62hp have indirect injection with pre-heat glow plugs.

Unusually the 62hp 5.280HE has five cylinders, which from my experience as a motoring writer testing Audis and Volkswagens, makes for a motor virtually as smooth as a line six but with less weight and complication.

When interviewed about the Nannidiesel range, Australian representative Peter Collins was quick to point out that the 43, 50 and 62hp models develop maximum power at only 2800rpm much lower than their Volvo and Yanmar competition.

According to Collins, not only does this reduce noise and vibration levels but also means the engines produce more torque at lower revs, important for heavier-displacement cruising yachts.

For example it's claimed the 5.280HE develops maximum torque of 166nm at 2100rpm, with 94% of this produced at just 1450rpm!

Because it's basically a tractor engine the 5.280HE has a massive 12lt sump almost twice the capacity of some automotive-based diesels of this horsepower. This reduces oil deterioration between changes as there's more oil circulating around in the sump.

Nannidiesel Australia has a computer program that allows yachties to choose exactly the right prop pitch for their particular application based on factors such as horsepower, RPM, reduction ratio, overall and waterline lengths and displacement. The resulting recommended prop dimensions ensure the motor will rarely overload when punching the boat in stiff headwinds and that the motor will be largely operated in its maximum torque band for the best engine efficiency and subsequently lower fuel consumption.

Another Nannidiesel feature is standard freshwater cooling the first full range of yacht auxiliaries in this country to be so fitted. This allows for hot water take-off for showers and keeps the engine at a higher, more constant operating temperature, creating lower exhaust emissions, less cylinder wall condensation during periods of disuse and lower mechanical noise levels.

The same model saildrive is used across the range and has a 2.2:1 gear ratio, while shaft drive models have the option of 2.0:1 or 2.5:1 and use mechanical Technodrive gearboxes.

HORSES FOR COURSES
Each of these makers' products have a range of benefits and some drawbacks. Personally, I like the traditional engineering and rugged simplicity of Bukh's offerings, particularly for full keel cruising yachts. But with their lower exhaust emissions, perhaps the Nannidiesels and Volvo's indirect injection range are more your style. By sheer weight of numbers, the freshwater-cooled indirect injection Yanmars are clearly a popular choice!

As much as any factor, we recommend you look hard at the area you cruise within and then find out about services and spares facilities in that region. Warranty and after-sales service, as much as any other factors, may sway your decision...